€•       Œsphinx.addnodes”Œdocument”“”)”}”(Œ	rawsource”Œ ”Œchildren”]”(Œtranslations”ŒLanguagesNode”“”)”}”(hhh]”(h Œpending_xref”“”)”}”(hhh]”Œdocutils.nodes”ŒText”“”ŒChinese (Simplified)”…””}”Œparent”hsbaŒ
attributes”}”(Œids”]”Œclasses”]”Œnames”]”Œdupnames”]”Œbackrefs”]”Œ	refdomain”Œstd”Œreftype”Œdoc”Œ	reftarget”Œ'/translations/zh_CN/livepatch/livepatch”Œmodname”NŒ	classname”NŒrefexplicit”ˆuŒtagname”hhhubh)”}”(hhh]”hŒChinese (Traditional)”…””}”hh2sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ'/translations/zh_TW/livepatch/livepatch”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒItalian”…””}”hhFsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ'/translations/it_IT/livepatch/livepatch”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒJapanese”…””}”hhZsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ'/translations/ja_JP/livepatch/livepatch”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒKorean”…””}”hhnsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ'/translations/ko_KR/livepatch/livepatch”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒSpanish”…””}”hh‚sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ'/translations/sp_SP/livepatch/livepatch”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubeh}”(h]”h ]”h"]”h$]”h&]”Œcurrent_language”ŒEnglish”uh1h
hhŒ	_document”hŒsource”NŒline”NubhŒsection”“”)”}”(hhh]”(hŒtitle”“”)”}”(hŒ	Livepatch”h]”hŒ	Livepatch”…””}”(hh¨hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¦hh£hžhhŸŒA/var/lib/git/docbuild/linux/Documentation/livepatch/livepatch.rst”h KubhŒ	paragraph”“”)”}”(hŒCThis document outlines basic information about kernel livepatching.”h]”hŒCThis document outlines basic information about kernel livepatching.”…””}”(hh¹hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khh£hžhubhŒcomment”“”)”}”(hŒTable of Contents:”h]”hŒTable of Contents:”…””}”hhÉsbah}”(h]”h ]”h"]”h$]”h&]”Œ	xml:space”Œpreserve”uh1hÇhh£hžhhŸh¶h KubhŒtopic”“”)”}”(hhh]”hŒbullet_list”“”)”}”(hhh]”(hŒ	list_item”“”)”}”(hhh]”h¸)”}”(hhh]”hŒ	reference”“”)”}”(hhh]”hŒ1. Motivation”…””}”(hhíhžhhŸNh Nubah}”(h]”Œid3”ah ]”h"]”h$]”h&]”Œrefid”Œ
motivation”uh1hëhhèubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hhåubah}”(h]”h ]”h"]”h$]”h&]”uh1hãhhàubhä)”}”(hhh]”h¸)”}”(hhh]”hì)”}”(hhh]”hŒ 2. Kprobes, Ftrace, Livepatching”…””}”(hj  hžhhŸNh Nubah}”(h]”Œid4”ah ]”h"]”h$]”h&]”Œrefid”Œkprobes-ftrace-livepatching”uh1hëhj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hj	  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hãhhàubhä)”}”(hhh]”(h¸)”}”(hhh]”hì)”}”(hhh]”hŒ3. Consistency model”…””}”(hj1  hžhhŸNh Nubah}”(h]”Œid5”ah ]”h"]”h$]”h&]”Œrefid”Œconsistency-model”uh1hëhj.  ubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hj+  ubhß)”}”(hhh]”hä)”}”(hhh]”h¸)”}”(hhh]”hì)”}”(hhh]”hŒ93.1 Adding consistency model support to new architectures”…””}”(hjP  hžhhŸNh Nubah}”(h]”Œid6”ah ]”h"]”h$]”h&]”Œrefid”Œ5adding-consistency-model-support-to-new-architectures”uh1hëhjM  ubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hjJ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hãhjG  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hÞhj+  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hãhhàubhä)”}”(hhh]”(h¸)”}”(hhh]”hì)”}”(hhh]”hŒ4. Livepatch module”…””}”(hj~  hžhhŸNh Nubah}”(h]”Œid7”ah ]”h"]”h$]”h&]”Œrefid”Œlivepatch-module”uh1hëhj{  ubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hjx  ubhß)”}”(hhh]”(hä)”}”(hhh]”h¸)”}”(hhh]”hì)”}”(hhh]”hŒ4.1. New functions”…””}”(hj  hžhhŸNh Nubah}”(h]”Œid8”ah ]”h"]”h$]”h&]”Œrefid”Œnew-functions”uh1hëhjš  ubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hj—  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hãhj”  ubhä)”}”(hhh]”h¸)”}”(hhh]”hì)”}”(hhh]”hŒ4.2. Metadata”…””}”(hj¿  hžhhŸNh Nubah}”(h]”Œid9”ah ]”h"]”h$]”h&]”Œrefid”Œmetadata”uh1hëhj¼  ubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hj¹  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hãhj”  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÞhjx  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hãhhàubhä)”}”(hhh]”(h¸)”}”(hhh]”hì)”}”(hhh]”hŒ5. Livepatch life-cycle”…””}”(hjí  hžhhŸNh Nubah}”(h]”Œid10”ah ]”h"]”h$]”h&]”Œrefid”Œlivepatch-life-cycle”uh1hëhjê  ubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hjç  ubhß)”}”(hhh]”(hä)”}”(hhh]”h¸)”}”(hhh]”hì)”}”(hhh]”hŒ5.1. Loading”…””}”(hj  hžhhŸNh Nubah}”(h]”Œid11”ah ]”h"]”h$]”h&]”Œrefid”Œloading”uh1hëhj	  ubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hãhj  ubhä)”}”(hhh]”h¸)”}”(hhh]”hì)”}”(hhh]”hŒ5.2. Enabling”…””}”(hj.  hžhhŸNh Nubah}”(h]”Œid12”ah ]”h"]”h$]”h&]”Œrefid”Œenabling”uh1hëhj+  ubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hj(  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hãhj  ubhä)”}”(hhh]”h¸)”}”(hhh]”hì)”}”(hhh]”hŒ5.3. Replacing”…””}”(hjP  hžhhŸNh Nubah}”(h]”Œid13”ah ]”h"]”h$]”h&]”Œrefid”Œ	replacing”uh1hëhjM  ubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hjJ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hãhj  ubhä)”}”(hhh]”h¸)”}”(hhh]”hì)”}”(hhh]”hŒ5.4. Disabling”…””}”(hjr  hžhhŸNh Nubah}”(h]”Œid14”ah ]”h"]”h$]”h&]”Œrefid”Œ	disabling”uh1hëhjo  ubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hjl  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hãhj  ubhä)”}”(hhh]”h¸)”}”(hhh]”hì)”}”(hhh]”hŒ5.5. Removing”…””}”(hj”  hžhhŸNh Nubah}”(h]”Œid15”ah ]”h"]”h$]”h&]”Œrefid”Œremoving”uh1hëhj‘  ubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hjŽ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hãhj  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÞhjç  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hãhhàubhä)”}”(hhh]”h¸)”}”(hhh]”hì)”}”(hhh]”hŒ6. Sysfs”…””}”(hjÂ  hžhhŸNh Nubah}”(h]”Œid16”ah ]”h"]”h$]”h&]”Œrefid”Œsysfs”uh1hëhj¿  ubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hj¼  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hãhhàubhä)”}”(hhh]”h¸)”}”(hhh]”hì)”}”(hhh]”hŒ7. Limitations”…””}”(hjä  hžhhŸNh Nubah}”(h]”Œid17”ah ]”h"]”h$]”h&]”Œrefid”Œlimitations”uh1hëhjá  ubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hjÞ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hãhhàubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÞhhÛhžhhŸNh Nubah}”(h]”Œcontents”ah ]”(Œcontents”Œlocal”eh"]”Œcontents”ah$]”h&]”uh1hÙhŸh¶h K
hh£hžhubh¢)”}”(hhh]”(h§)”}”(hŒ1. Motivation”h]”hŒ1. Motivation”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”Œrefid”höuh1h¦hj  hžhhŸh¶h Kubh¸)”}”(hX¦  There are many situations where users are reluctant to reboot a system. It may
be because their system is performing complex scientific computations or under
heavy load during peak usage. In addition to keeping systems up and running,
users want to also have a stable and secure system. Livepatching gives users
both by allowing for function calls to be redirected; thus, fixing critical
functions without a system reboot.”h]”hX¦  There are many situations where users are reluctant to reboot a system. It may
be because their system is performing complex scientific computations or under
heavy load during peak usage. In addition to keeping systems up and running,
users want to also have a stable and secure system. Livepatching gives users
both by allowing for function calls to be redirected; thus, fixing critical
functions without a system reboot.”…””}”(hj"  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khj  hžhubeh}”(h]”hüah ]”h"]”Œ1. motivation”ah$]”h&]”uh1h¡hh£hžhhŸh¶h Kubh¢)”}”(hhh]”(h§)”}”(hŒ 2. Kprobes, Ftrace, Livepatching”h]”hŒ 2. Kprobes, Ftrace, Livepatching”…””}”(hj:  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”j!  j  uh1h¦hj7  hžhhŸh¶h Kubh¸)”}”(hŒ¨There are multiple mechanisms in the Linux kernel that are directly related
to redirection of code execution; namely: kernel probes, function tracing,
and livepatching:”h]”hŒ¨There are multiple mechanisms in the Linux kernel that are directly related
to redirection of code execution; namely: kernel probes, function tracing,
and livepatching:”…””}”(hjH  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khj7  hžhubhŒblock_quote”“”)”}”(hXè  - The kernel probes are the most generic. The code can be redirected by
  putting a breakpoint instruction instead of any instruction.

- The function tracer calls the code from a predefined location that is
  close to the function entry point. This location is generated by the
  compiler using the '-pg' gcc option.

- Livepatching typically needs to redirect the code at the very beginning
  of the function entry before the function parameters or the stack
  are in any way modified.
”h]”hß)”}”(hhh]”(hä)”}”(hŒƒThe kernel probes are the most generic. The code can be redirected by
putting a breakpoint instruction instead of any instruction.
”h]”h¸)”}”(hŒ‚The kernel probes are the most generic. The code can be redirected by
putting a breakpoint instruction instead of any instruction.”h]”hŒ‚The kernel probes are the most generic. The code can be redirected by
putting a breakpoint instruction instead of any instruction.”…””}”(hjc  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khj_  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hãhj\  ubhä)”}”(hŒ°The function tracer calls the code from a predefined location that is
close to the function entry point. This location is generated by the
compiler using the '-pg' gcc option.
”h]”h¸)”}”(hŒ¯The function tracer calls the code from a predefined location that is
close to the function entry point. This location is generated by the
compiler using the '-pg' gcc option.”h]”hŒ³The function tracer calls the code from a predefined location that is
close to the function entry point. This location is generated by the
compiler using the â€˜-pgâ€™ gcc option.”…””}”(hj{  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K!hjw  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hãhj\  ubhä)”}”(hŒ£Livepatching typically needs to redirect the code at the very beginning
of the function entry before the function parameters or the stack
are in any way modified.
”h]”h¸)”}”(hŒ¢Livepatching typically needs to redirect the code at the very beginning
of the function entry before the function parameters or the stack
are in any way modified.”h]”hŒ¢Livepatching typically needs to redirect the code at the very beginning
of the function entry before the function parameters or the stack
are in any way modified.”…””}”(hj“  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K%hj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hãhj\  ubeh}”(h]”h ]”h"]”h$]”h&]”Œbullet”Œ-”uh1hÞhŸh¶h KhjX  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jV  hŸh¶h Khj7  hžhubh¸)”}”(hXá  All three approaches need to modify the existing code at runtime. Therefore
they need to be aware of each other and not step over each other's toes.
Most of these problems are solved by using the dynamic ftrace framework as
a base. A Kprobe is registered as a ftrace handler when the function entry
is probed, see CONFIG_KPROBES_ON_FTRACE. Also an alternative function from
a live patch is called with the help of a custom ftrace handler. But there are
some limitations, see below.”h]”hXã  All three approaches need to modify the existing code at runtime. Therefore
they need to be aware of each other and not step over each otherâ€™s toes.
Most of these problems are solved by using the dynamic ftrace framework as
a base. A Kprobe is registered as a ftrace handler when the function entry
is probed, see CONFIG_KPROBES_ON_FTRACE. Also an alternative function from
a live patch is called with the help of a custom ftrace handler. But there are
some limitations, see below.”…””}”(hjµ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K)hj7  hžhubeh}”(h]”j  ah ]”h"]”Œ 2. kprobes, ftrace, livepatching”ah$]”h&]”uh1h¡hh£hžhhŸh¶h Kubh¢)”}”(hhh]”(h§)”}”(hŒ3. Consistency model”h]”hŒ3. Consistency model”…””}”(hjÍ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”j!  j:  uh1h¦hjÊ  hžhhŸh¶h K3ubh¸)”}”(hŒàFunctions are there for a reason. They take some input parameters, acquire or
release locks, read, process, and even write some data in a defined way,
have return values. In other words, each function has a defined semantic.”h]”hŒàFunctions are there for a reason. They take some input parameters, acquire or
release locks, read, process, and even write some data in a defined way,
have return values. In other words, each function has a defined semantic.”…””}”(hjÛ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K5hjÊ  hžhubh¸)”}”(hX‘  Many fixes do not change the semantic of the modified functions. For
example, they add a NULL pointer or a boundary check, fix a race by adding
a missing memory barrier, or add some locking around a critical section.
Most of these changes are self contained and the function presents itself
the same way to the rest of the system. In this case, the functions might
be updated independently one by one.”h]”hX‘  Many fixes do not change the semantic of the modified functions. For
example, they add a NULL pointer or a boundary check, fix a race by adding
a missing memory barrier, or add some locking around a critical section.
Most of these changes are self contained and the function presents itself
the same way to the rest of the system. In this case, the functions might
be updated independently one by one.”…””}”(hjé  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K9hjÊ  hžhubh¸)”}”(hX	  But there are more complex fixes. For example, a patch might change
ordering of locking in multiple functions at the same time. Or a patch
might exchange meaning of some temporary structures and update
all the relevant functions. In this case, the affected unit
(thread, whole kernel) need to start using all new versions of
the functions at the same time. Also the switch must happen only
when it is safe to do so, e.g. when the affected locks are released
or no data are stored in the modified structures at the moment.”h]”hX	  But there are more complex fixes. For example, a patch might change
ordering of locking in multiple functions at the same time. Or a patch
might exchange meaning of some temporary structures and update
all the relevant functions. In this case, the affected unit
(thread, whole kernel) need to start using all new versions of
the functions at the same time. Also the switch must happen only
when it is safe to do so, e.g. when the affected locks are released
or no data are stored in the modified structures at the moment.”…””}”(hj÷  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K@hjÊ  hžhubh¸)”}”(hŒéThe theory about how to apply functions a safe way is rather complex.
The aim is to define a so-called consistency model. It attempts to define
conditions when the new implementation could be used so that the system
stays consistent.”h]”hŒéThe theory about how to apply functions a safe way is rather complex.
The aim is to define a so-called consistency model. It attempts to define
conditions when the new implementation could be used so that the system
stays consistent.”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KIhjÊ  hžhubh¸)”}”(hX  Livepatch has a consistency model which is a hybrid of kGraft and
kpatch:  it uses kGraft's per-task consistency and syscall barrier
switching combined with kpatch's stack trace switching.  There are also
a number of fallback options which make it quite flexible.”h]”hX  Livepatch has a consistency model which is a hybrid of kGraft and
kpatch:  it uses kGraftâ€™s per-task consistency and syscall barrier
switching combined with kpatchâ€™s stack trace switching.  There are also
a number of fallback options which make it quite flexible.”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KNhjÊ  hžhubh¸)”}”(hXƒ  Patches are applied on a per-task basis, when the task is deemed safe to
switch over.  When a patch is enabled, livepatch enters into a
transition state where tasks are converging to the patched state.
Usually this transition state can complete in a few seconds.  The same
sequence occurs when a patch is disabled, except the tasks converge from
the patched state to the unpatched state.”h]”hXƒ  Patches are applied on a per-task basis, when the task is deemed safe to
switch over.  When a patch is enabled, livepatch enters into a
transition state where tasks are converging to the patched state.
Usually this transition state can complete in a few seconds.  The same
sequence occurs when a patch is disabled, except the tasks converge from
the patched state to the unpatched state.”…””}”(hj!  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KShjÊ  hžhubh¸)”}”(hŒ¢An interrupt handler inherits the patched state of the task it
interrupts.  The same is true for forked tasks: the child inherits the
patched state of the parent.”h]”hŒ¢An interrupt handler inherits the patched state of the task it
interrupts.  The same is true for forked tasks: the child inherits the
patched state of the parent.”…””}”(hj/  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KZhjÊ  hžhubh¸)”}”(hŒ[Livepatch uses several complementary approaches to determine when it's
safe to patch tasks:”h]”hŒ]Livepatch uses several complementary approaches to determine when itâ€™s
safe to patch tasks:”…””}”(hj=  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K^hjÊ  hžhubhŒenumerated_list”“”)”}”(hhh]”(hä)”}”(hXt  The first and most effective approach is stack checking of sleeping
tasks.  If no affected functions are on the stack of a given task,
the task is patched.  In most cases this will patch most or all of
the tasks on the first try.  Otherwise it'll keep trying
periodically.  This option is only available if the architecture has
reliable stacks (HAVE_RELIABLE_STACKTRACE).
”h]”h¸)”}”(hXs  The first and most effective approach is stack checking of sleeping
tasks.  If no affected functions are on the stack of a given task,
the task is patched.  In most cases this will patch most or all of
the tasks on the first try.  Otherwise it'll keep trying
periodically.  This option is only available if the architecture has
reliable stacks (HAVE_RELIABLE_STACKTRACE).”h]”hXu  The first and most effective approach is stack checking of sleeping
tasks.  If no affected functions are on the stack of a given task,
the task is patched.  In most cases this will patch most or all of
the tasks on the first try.  Otherwise itâ€™ll keep trying
periodically.  This option is only available if the architecture has
reliable stacks (HAVE_RELIABLE_STACKTRACE).”…””}”(hjT  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KahjP  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hãhjM  hžhhŸh¶h Nubhä)”}”(hX	  The second approach, if needed, is kernel exit switching.  A
task is switched when it returns to user space from a system call, a
user space IRQ, or a signal.  It's useful in the following cases:

a) Patching I/O-bound user tasks which are sleeping on an affected
   function.  In this case you have to send SIGSTOP and SIGCONT to
   force it to exit the kernel and be patched.
b) Patching CPU-bound user tasks.  If the task is highly CPU-bound
   then it will get patched the next time it gets interrupted by an
   IRQ.
”h]”(h¸)”}”(hŒÃThe second approach, if needed, is kernel exit switching.  A
task is switched when it returns to user space from a system call, a
user space IRQ, or a signal.  It's useful in the following cases:”h]”hŒÅThe second approach, if needed, is kernel exit switching.  A
task is switched when it returns to user space from a system call, a
user space IRQ, or a signal.  Itâ€™s useful in the following cases:”…””}”(hjl  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khhjh  ubjL  )”}”(hhh]”(hä)”}”(hŒ«Patching I/O-bound user tasks which are sleeping on an affected
function.  In this case you have to send SIGSTOP and SIGCONT to
force it to exit the kernel and be patched.”h]”h¸)”}”(hŒ«Patching I/O-bound user tasks which are sleeping on an affected
function.  In this case you have to send SIGSTOP and SIGCONT to
force it to exit the kernel and be patched.”h]”hŒ«Patching I/O-bound user tasks which are sleeping on an affected
function.  In this case you have to send SIGSTOP and SIGCONT to
force it to exit the kernel and be patched.”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Klhj}  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hãhjz  ubhä)”}”(hŒ†Patching CPU-bound user tasks.  If the task is highly CPU-bound
then it will get patched the next time it gets interrupted by an
IRQ.
”h]”h¸)”}”(hŒ…Patching CPU-bound user tasks.  If the task is highly CPU-bound
then it will get patched the next time it gets interrupted by an
IRQ.”h]”hŒ…Patching CPU-bound user tasks.  If the task is highly CPU-bound
then it will get patched the next time it gets interrupted by an
IRQ.”…””}”(hj™  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Kohj•  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hãhjz  ubeh}”(h]”h ]”h"]”h$]”h&]”Œenumtype”Œ
loweralpha”Œprefix”hŒsuffix”Œ)”uh1jK  hjh  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hãhjM  hžhhŸNh Nubhä)”}”(hX  For idle "swapper" tasks, since they don't ever exit the kernel, they
instead have a klp_update_patch_state() call in the idle loop which
allows them to be patched before the CPU enters the idle state.

(Note there's not yet such an approach for kthreads.)
”h]”(h¸)”}”(hŒÉFor idle "swapper" tasks, since they don't ever exit the kernel, they
instead have a klp_update_patch_state() call in the idle loop which
allows them to be patched before the CPU enters the idle state.”h]”hŒÏFor idle â€œswapperâ€ tasks, since they donâ€™t ever exit the kernel, they
instead have a klp_update_patch_state() call in the idle loop which
allows them to be patched before the CPU enters the idle state.”…””}”(hjÂ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Kshj¾  ubh¸)”}”(hŒ5(Note there's not yet such an approach for kthreads.)”h]”hŒ7(Note thereâ€™s not yet such an approach for kthreads.)”…””}”(hjÐ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Kwhj¾  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hãhjM  hžhhŸh¶h Nubeh}”(h]”h ]”h"]”h$]”h&]”j³  Œarabic”jµ  hj¶  Œ.”uh1jK  hjÊ  hžhhŸh¶h Kaubh¸)”}”(hX  Architectures which don't have HAVE_RELIABLE_STACKTRACE solely rely on
the second approach. It's highly likely that some tasks may still be
running with an old version of the function, until that function
returns. In this case you would have to signal the tasks. This
especially applies to kthreads. They may not be woken up and would need
to be forced. See below for more information.”h]”hX…  Architectures which donâ€™t have HAVE_RELIABLE_STACKTRACE solely rely on
the second approach. Itâ€™s highly likely that some tasks may still be
running with an old version of the function, until that function
returns. In this case you would have to signal the tasks. This
especially applies to kthreads. They may not be woken up and would need
to be forced. See below for more information.”…””}”(hjì  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KyhjÊ  hžhubh¸)”}”(hŒ§Unless we can come up with another way to patch kthreads, architectures
without HAVE_RELIABLE_STACKTRACE are not considered fully supported by
the kernel livepatching.”h]”hŒ§Unless we can come up with another way to patch kthreads, architectures
without HAVE_RELIABLE_STACKTRACE are not considered fully supported by
the kernel livepatching.”…””}”(hjú  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K€hjÊ  hžhubh¸)”}”(hŒþThe /sys/kernel/livepatch/<patch>/transition file shows whether a patch
is in transition.  Only a single patch can be in transition at a given
time.  A patch can remain in transition indefinitely, if any of the tasks
are stuck in the initial patch state.”h]”hŒþThe /sys/kernel/livepatch/<patch>/transition file shows whether a patch
is in transition.  Only a single patch can be in transition at a given
time.  A patch can remain in transition indefinitely, if any of the tasks
are stuck in the initial patch state.”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K„hjÊ  hžhubh¸)”}”(hŒùA transition can be reversed and effectively canceled by writing the
opposite value to the /sys/kernel/livepatch/<patch>/enabled file while
the transition is in progress.  Then all the tasks will attempt to
converge back to the original patch state.”h]”hŒùA transition can be reversed and effectively canceled by writing the
opposite value to the /sys/kernel/livepatch/<patch>/enabled file while
the transition is in progress.  Then all the tasks will attempt to
converge back to the original patch state.”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K‰hjÊ  hžhubh¸)”}”(hX  There's also a /proc/<pid>/patch_state file which can be used to
determine which tasks are blocking completion of a patching operation.
If a patch is in transition, this file shows 0 to indicate the task is
unpatched and 1 to indicate it's patched.  Otherwise, if no patch is in
transition, it shows -1.  Any tasks which are blocking the transition
can be signaled with SIGSTOP and SIGCONT to force them to change their
patched state. This may be harmful to the system though. Sending a fake signal
to all remaining blocking tasks is a better alternative. No proper signal is
actually delivered (there is no data in signal pending structures). Tasks are
interrupted or woken up, and forced to change their patched state. The fake
signal is automatically sent every 15 seconds.”h]”hX  Thereâ€™s also a /proc/<pid>/patch_state file which can be used to
determine which tasks are blocking completion of a patching operation.
If a patch is in transition, this file shows 0 to indicate the task is
unpatched and 1 to indicate itâ€™s patched.  Otherwise, if no patch is in
transition, it shows -1.  Any tasks which are blocking the transition
can be signaled with SIGSTOP and SIGCONT to force them to change their
patched state. This may be harmful to the system though. Sending a fake signal
to all remaining blocking tasks is a better alternative. No proper signal is
actually delivered (there is no data in signal pending structures). Tasks are
interrupted or woken up, and forced to change their patched state. The fake
signal is automatically sent every 15 seconds.”…””}”(hj$  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KŽhjÊ  hžhubh¸)”}”(hXÈ  Administrator can also affect a transition through
/sys/kernel/livepatch/<patch>/force attribute. Writing 1 there clears
TIF_PATCH_PENDING flag of all tasks and thus forces the tasks to the patched
state. Important note! The force attribute is intended for cases when the
transition gets stuck for a long time because of a blocking task. Administrator
is expected to collect all necessary data (namely stack traces of such blocking
tasks) and request a clearance from a patch distributor to force the transition.
Unauthorized usage may cause harm to the system. It depends on the nature of the
patch, which functions are (un)patched, and which functions the blocking tasks
are sleeping in (/proc/<pid>/stack may help here). Removal (rmmod) of patch
modules is permanently disabled when the force feature is used. It cannot be
guaranteed there is no task sleeping in such module. It implies unbounded
reference count if a patch module is disabled and enabled in a loop.”h]”hXÈ  Administrator can also affect a transition through
/sys/kernel/livepatch/<patch>/force attribute. Writing 1 there clears
TIF_PATCH_PENDING flag of all tasks and thus forces the tasks to the patched
state. Important note! The force attribute is intended for cases when the
transition gets stuck for a long time because of a blocking task. Administrator
is expected to collect all necessary data (namely stack traces of such blocking
tasks) and request a clearance from a patch distributor to force the transition.
Unauthorized usage may cause harm to the system. It depends on the nature of the
patch, which functions are (un)patched, and which functions the blocking tasks
are sleeping in (/proc/<pid>/stack may help here). Removal (rmmod) of patch
modules is permanently disabled when the force feature is used. It cannot be
guaranteed there is no task sleeping in such module. It implies unbounded
reference count if a patch module is disabled and enabled in a loop.”…””}”(hj2  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KšhjÊ  hžhubh¸)”}”(hX  Moreover, the usage of force may also affect future applications of live
patches and cause even more harm to the system. Administrator should first
consider to simply cancel a transition (see above). If force is used, reboot
should be planned and no more live patches applied.”h]”hX  Moreover, the usage of force may also affect future applications of live
patches and cause even more harm to the system. Administrator should first
consider to simply cancel a transition (see above). If force is used, reboot
should be planned and no more live patches applied.”…””}”(hj@  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K¨hjÊ  hžhubh¢)”}”(hhh]”(h§)”}”(hŒ93.1 Adding consistency model support to new architectures”h]”hŒ93.1 Adding consistency model support to new architectures”…””}”(hjQ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”j!  jY  uh1h¦hjN  hžhhŸh¶h K®ubh¸)”}”(hŒSFor adding consistency model support to new architectures, there are a
few options:”h]”hŒSFor adding consistency model support to new architectures, there are a
few options:”…””}”(hj_  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K°hjN  hžhubjL  )”}”(hhh]”(hä)”}”(hŒ¼Add CONFIG_HAVE_RELIABLE_STACKTRACE.  This means porting objtool, and
for non-DWARF unwinders, also making sure there's a way for the stack
tracing code to detect interrupts on the stack.
”h]”h¸)”}”(hŒ»Add CONFIG_HAVE_RELIABLE_STACKTRACE.  This means porting objtool, and
for non-DWARF unwinders, also making sure there's a way for the stack
tracing code to detect interrupts on the stack.”h]”hŒ½Add CONFIG_HAVE_RELIABLE_STACKTRACE.  This means porting objtool, and
for non-DWARF unwinders, also making sure thereâ€™s a way for the stack
tracing code to detect interrupts on the stack.”…””}”(hjt  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K³hjp  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hãhjm  hžhhŸh¶h Nubhä)”}”(hXƒ  Alternatively, ensure that every kthread has a call to
klp_update_patch_state() in a safe location.  Kthreads are typically
in an infinite loop which does some action repeatedly.  The safe
location to switch the kthread's patch state would be at a designated
point in the loop where there are no locks taken and all data
structures are in a well-defined state.

The location is clear when using workqueues or the kthread worker
API.  These kthreads process independent actions in a generic loop.

It's much more complicated with kthreads which have a custom loop.
There the safe location must be carefully selected on a case-by-case
basis.

In that case, arches without HAVE_RELIABLE_STACKTRACE would still be
able to use the non-stack-checking parts of the consistency model:

a) patching user tasks when they cross the kernel/user space
   boundary; and

b) patching kthreads and idle tasks at their designated patch points.

This option isn't as good as option 1 because it requires signaling
user tasks and waking kthreads to patch them.  But it could still be
a good backup option for those architectures which don't have
reliable stack traces yet.

”h]”(h¸)”}”(hXh  Alternatively, ensure that every kthread has a call to
klp_update_patch_state() in a safe location.  Kthreads are typically
in an infinite loop which does some action repeatedly.  The safe
location to switch the kthread's patch state would be at a designated
point in the loop where there are no locks taken and all data
structures are in a well-defined state.”h]”hXj  Alternatively, ensure that every kthread has a call to
klp_update_patch_state() in a safe location.  Kthreads are typically
in an infinite loop which does some action repeatedly.  The safe
location to switch the kthreadâ€™s patch state would be at a designated
point in the loop where there are no locks taken and all data
structures are in a well-defined state.”…””}”(hjŒ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K·hjˆ  ubh¸)”}”(hŒ…The location is clear when using workqueues or the kthread worker
API.  These kthreads process independent actions in a generic loop.”h]”hŒ…The location is clear when using workqueues or the kthread worker
API.  These kthreads process independent actions in a generic loop.”…””}”(hjš  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K¾hjˆ  ubh¸)”}”(hŒŽIt's much more complicated with kthreads which have a custom loop.
There the safe location must be carefully selected on a case-by-case
basis.”h]”hŒItâ€™s much more complicated with kthreads which have a custom loop.
There the safe location must be carefully selected on a case-by-case
basis.”…””}”(hj¨  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KÁhjˆ  ubh¸)”}”(hŒ‡In that case, arches without HAVE_RELIABLE_STACKTRACE would still be
able to use the non-stack-checking parts of the consistency model:”h]”hŒ‡In that case, arches without HAVE_RELIABLE_STACKTRACE would still be
able to use the non-stack-checking parts of the consistency model:”…””}”(hj¶  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KÅhjˆ  ubjL  )”}”(hhh]”(hä)”}”(hŒHpatching user tasks when they cross the kernel/user space
boundary; and
”h]”h¸)”}”(hŒGpatching user tasks when they cross the kernel/user space
boundary; and”h]”hŒGpatching user tasks when they cross the kernel/user space
boundary; and”…””}”(hjË  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KÈhjÇ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hãhjÄ  ubhä)”}”(hŒCpatching kthreads and idle tasks at their designated patch points.
”h]”h¸)”}”(hŒBpatching kthreads and idle tasks at their designated patch points.”h]”hŒBpatching kthreads and idle tasks at their designated patch points.”…””}”(hjã  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KËhjß  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hãhjÄ  ubeh}”(h]”h ]”h"]”h$]”h&]”j³  j´  jµ  hj¶  j·  uh1jK  hjˆ  ubh¸)”}”(hŒáThis option isn't as good as option 1 because it requires signaling
user tasks and waking kthreads to patch them.  But it could still be
a good backup option for those architectures which don't have
reliable stack traces yet.”h]”hŒåThis option isnâ€™t as good as option 1 because it requires signaling
user tasks and waking kthreads to patch them.  But it could still be
a good backup option for those architectures which donâ€™t have
reliable stack traces yet.”…””}”(hjý  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KÍhjˆ  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hãhjm  hžhhŸh¶h Nubeh}”(h]”h ]”h"]”h$]”h&]”j³  jê  jµ  hj¶  j·  uh1jK  hjN  hžhhŸh¶h K³ubeh}”(h]”j_  ah ]”h"]”Œ93.1 adding consistency model support to new architectures”ah$]”h&]”uh1h¡hjÊ  hžhhŸh¶h K®ubeh}”(h]”j@  ah ]”h"]”Œ3. consistency model”ah$]”h&]”uh1h¡hh£hžhhŸh¶h K3ubh¢)”}”(hhh]”(h§)”}”(hŒ4. Livepatch module”h]”hŒ4. Livepatch module”…””}”(hj(  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”j!  j‡  uh1h¦hj%  hžhhŸh¶h KÔubh¸)”}”(hŒ[Livepatches are distributed using kernel modules, see
samples/livepatch/livepatch-sample.c.”h]”hŒ[Livepatches are distributed using kernel modules, see
samples/livepatch/livepatch-sample.c.”…””}”(hj6  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KÖhj%  hžhubh¸)”}”(hX¬  The module includes a new implementation of functions that we want
to replace. In addition, it defines some structures describing the
relation between the original and the new implementation. Then there
is code that makes the kernel start using the new code when the livepatch
module is loaded. Also there is code that cleans up before the
livepatch module is removed. All this is explained in more details in
the next sections.”h]”hX¬  The module includes a new implementation of functions that we want
to replace. In addition, it defines some structures describing the
relation between the original and the new implementation. Then there
is code that makes the kernel start using the new code when the livepatch
module is loaded. Also there is code that cleans up before the
livepatch module is removed. All this is explained in more details in
the next sections.”…””}”(hjD  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KÙhj%  hžhubh¢)”}”(hhh]”(h§)”}”(hŒ4.1. New functions”h]”hŒ4.1. New functions”…””}”(hjU  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”j!  j¦  uh1h¦hjR  hžhhŸh¶h Kãubh¸)”}”(hX=  New versions of functions are typically just copied from the original
sources. A good practice is to add a prefix to the names so that they
can be distinguished from the original ones, e.g. in a backtrace. Also
they can be declared as static because they are not called directly
and do not need the global visibility.”h]”hX=  New versions of functions are typically just copied from the original
sources. A good practice is to add a prefix to the names so that they
can be distinguished from the original ones, e.g. in a backtrace. Also
they can be declared as static because they are not called directly
and do not need the global visibility.”…””}”(hjc  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KåhjR  hžhubh¸)”}”(hXH  The patch contains only functions that are really modified. But they
might want to access functions or data from the original source file
that may only be locally accessible. This can be solved by a special
relocation section in the generated livepatch module, see
Documentation/livepatch/module-elf-format.rst for more details.”h]”hXH  The patch contains only functions that are really modified. But they
might want to access functions or data from the original source file
that may only be locally accessible. This can be solved by a special
relocation section in the generated livepatch module, see
Documentation/livepatch/module-elf-format.rst for more details.”…””}”(hjq  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KëhjR  hžhubeh}”(h]”j¬  ah ]”h"]”Œ4.1. new functions”ah$]”h&]”uh1h¡hj%  hžhhŸh¶h Kãubh¢)”}”(hhh]”(h§)”}”(hŒ4.2. Metadata”h]”hŒ4.2. Metadata”…””}”(hj‰  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”j!  jÈ  uh1h¦hj†  hžhhŸh¶h Kóubh¸)”}”(hŒZThe patch is described by several structures that split the information
into three levels:”h]”hŒZThe patch is described by several structures that split the information
into three levels:”…””}”(hj—  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Kõhj†  hžhubjW  )”}”(hX”  - struct klp_func is defined for each patched function. It describes
  the relation between the original and the new implementation of a
  particular function.

  The structure includes the name, as a string, of the original function.
  The function address is found via kallsyms at runtime.

  Then it includes the address of the new function. It is defined
  directly by assigning the function pointer. Note that the new
  function is typically defined in the same source file.

  As an optional parameter, the symbol position in the kallsyms database can
  be used to disambiguate functions of the same name. This is not the
  absolute position in the database, but rather the order it has been found
  only for a particular object ( vmlinux or a kernel module ). Note that
  kallsyms allows for searching symbols according to the object name.

- struct klp_object defines an array of patched functions (struct
  klp_func) in the same object. Where the object is either vmlinux
  (NULL) or a module name.

  The structure helps to group and handle functions for each object
  together. Note that patched modules might be loaded later than
  the patch itself and the relevant functions might be patched
  only when they are available.


- struct klp_patch defines an array of patched objects (struct
  klp_object).

  This structure handles all patched functions consistently and eventually,
  synchronously. The whole patch is applied only when all patched
  symbols are found. The only exception are symbols from objects
  (kernel modules) that have not been loaded yet.

  For more details on how the patch is applied on a per-task basis,
  see the "Consistency model" section.

”h]”hß)”}”(hhh]”(hä)”}”(hX5  struct klp_func is defined for each patched function. It describes
the relation between the original and the new implementation of a
particular function.

The structure includes the name, as a string, of the original function.
The function address is found via kallsyms at runtime.

Then it includes the address of the new function. It is defined
directly by assigning the function pointer. Note that the new
function is typically defined in the same source file.

As an optional parameter, the symbol position in the kallsyms database can
be used to disambiguate functions of the same name. This is not the
absolute position in the database, but rather the order it has been found
only for a particular object ( vmlinux or a kernel module ). Note that
kallsyms allows for searching symbols according to the object name.
”h]”(h¸)”}”(hŒ™struct klp_func is defined for each patched function. It describes
the relation between the original and the new implementation of a
particular function.”h]”hŒ™struct klp_func is defined for each patched function. It describes
the relation between the original and the new implementation of a
particular function.”…””}”(hj°  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Køhj¬  ubh¸)”}”(hŒ~The structure includes the name, as a string, of the original function.
The function address is found via kallsyms at runtime.”h]”hŒ~The structure includes the name, as a string, of the original function.
The function address is found via kallsyms at runtime.”…””}”(hj¾  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Kühj¬  ubh¸)”}”(hŒ´Then it includes the address of the new function. It is defined
directly by assigning the function pointer. Note that the new
function is typically defined in the same source file.”h]”hŒ´Then it includes the address of the new function. It is defined
directly by assigning the function pointer. Note that the new
function is typically defined in the same source file.”…””}”(hjÌ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Kÿhj¬  ubh¸)”}”(hXc  As an optional parameter, the symbol position in the kallsyms database can
be used to disambiguate functions of the same name. This is not the
absolute position in the database, but rather the order it has been found
only for a particular object ( vmlinux or a kernel module ). Note that
kallsyms allows for searching symbols according to the object name.”h]”hXc  As an optional parameter, the symbol position in the kallsyms database can
be used to disambiguate functions of the same name. This is not the
absolute position in the database, but rather the order it has been found
only for a particular object ( vmlinux or a kernel module ). Note that
kallsyms allows for searching symbols according to the object name.”…””}”(hjÚ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Mhj¬  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hãhj©  ubhä)”}”(hXx  struct klp_object defines an array of patched functions (struct
klp_func) in the same object. Where the object is either vmlinux
(NULL) or a module name.

The structure helps to group and handle functions for each object
together. Note that patched modules might be loaded later than
the patch itself and the relevant functions might be patched
only when they are available.

”h]”(h¸)”}”(hŒ™struct klp_object defines an array of patched functions (struct
klp_func) in the same object. Where the object is either vmlinux
(NULL) or a module name.”h]”hŒ™struct klp_object defines an array of patched functions (struct
klp_func) in the same object. Where the object is either vmlinux
(NULL) or a module name.”…””}”(hjò  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h M	hjî  ubh¸)”}”(hŒÛThe structure helps to group and handle functions for each object
together. Note that patched modules might be loaded later than
the patch itself and the relevant functions might be patched
only when they are available.”h]”hŒÛThe structure helps to group and handle functions for each object
together. Note that patched modules might be loaded later than
the patch itself and the relevant functions might be patched
only when they are available.”…””}”(hj   hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Mhjî  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hãhj©  ubhä)”}”(hX­  struct klp_patch defines an array of patched objects (struct
klp_object).

This structure handles all patched functions consistently and eventually,
synchronously. The whole patch is applied only when all patched
symbols are found. The only exception are symbols from objects
(kernel modules) that have not been loaded yet.

For more details on how the patch is applied on a per-task basis,
see the "Consistency model" section.

”h]”(h¸)”}”(hŒIstruct klp_patch defines an array of patched objects (struct
klp_object).”h]”hŒIstruct klp_patch defines an array of patched objects (struct
klp_object).”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Mhj  ubh¸)”}”(hŒøThis structure handles all patched functions consistently and eventually,
synchronously. The whole patch is applied only when all patched
symbols are found. The only exception are symbols from objects
(kernel modules) that have not been loaded yet.”h]”hŒøThis structure handles all patched functions consistently and eventually,
synchronously. The whole patch is applied only when all patched
symbols are found. The only exception are symbols from objects
(kernel modules) that have not been loaded yet.”…””}”(hj&  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Mhj  ubh¸)”}”(hŒfFor more details on how the patch is applied on a per-task basis,
see the "Consistency model" section.”h]”hŒjFor more details on how the patch is applied on a per-task basis,
see the â€œConsistency modelâ€ section.”…””}”(hj4  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Mhj  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hãhj©  ubeh}”(h]”h ]”h"]”h$]”h&]”j­  j®  uh1hÞhŸh¶h Køhj¥  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jV  hŸh¶h Køhj†  hžhubeh}”(h]”jÎ  ah ]”h"]”Œ4.2. metadata”ah$]”h&]”uh1h¡hj%  hžhhŸh¶h Kóubeh}”(h]”j  ah ]”h"]”Œ4. livepatch module”ah$]”h&]”uh1h¡hh£hžhhŸh¶h KÔubh¢)”}”(hhh]”(h§)”}”(hŒ5. Livepatch life-cycle”h]”hŒ5. Livepatch life-cycle”…””}”(hje  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”j!  jö  uh1h¦hjb  hžhhŸh¶h M ubh¸)”}”(hŒjLivepatching can be described by five basic operations:
loading, enabling, replacing, disabling, removing.”h]”hŒjLivepatching can be described by five basic operations:
loading, enabling, replacing, disabling, removing.”…””}”(hjs  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h M"hjb  hžhubh¸)”}”(hŒŽWhere the replacing and the disabling operations are mutually
exclusive. They have the same result for the given patch but
not for the system.”h]”hŒŽWhere the replacing and the disabling operations are mutually
exclusive. They have the same result for the given patch but
not for the system.”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h M%hjb  hžhubh¢)”}”(hhh]”(h§)”}”(hŒ5.1. Loading”h]”hŒ5.1. Loading”…””}”(hj’  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”j!  j  uh1h¦hj  hžhhŸh¶h M+ubh¸)”}”(hŒÉThe only reasonable way is to enable the patch when the livepatch kernel
module is being loaded. For this, klp_enable_patch() has to be called
in the module_init() callback. There are two main reasons:”h]”hŒÉThe only reasonable way is to enable the patch when the livepatch kernel
module is being loaded. For this, klp_enable_patch() has to be called
in the module_init() callback. There are two main reasons:”…””}”(hj   hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h M-hj  hžhubh¸)”}”(hŒJFirst, only the module has an easy access to the related struct klp_patch.”h]”hŒJFirst, only the module has an easy access to the related struct klp_patch.”…””}”(hj®  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h M1hj  hžhubh¸)”}”(hŒdSecond, the error code might be used to refuse loading the module when
the patch cannot get enabled.”h]”hŒdSecond, the error code might be used to refuse loading the module when
the patch cannot get enabled.”…””}”(hj¼  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h M3hj  hžhubeh}”(h]”j  ah ]”h"]”Œ5.1. loading”ah$]”h&]”uh1h¡hjb  hžhhŸh¶h M+ubh¢)”}”(hhh]”(h§)”}”(hŒ5.2. Enabling”h]”hŒ5.2. Enabling”…””}”(hjÔ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”j!  j7  uh1h¦hjÑ  hžhhŸh¶h M8ubh¸)”}”(hŒ´The livepatch gets enabled by calling klp_enable_patch() from
the module_init() callback. The system will start using the new
implementation of the patched functions at this stage.”h]”hŒ´The livepatch gets enabled by calling klp_enable_patch() from
the module_init() callback. The system will start using the new
implementation of the patched functions at this stage.”…””}”(hjâ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h M:hjÑ  hžhubh¸)”}”(hX  First, the addresses of the patched functions are found according to their
names. The special relocations, mentioned in the section "New functions",
are applied. The relevant entries are created under
/sys/kernel/livepatch/<name>. The patch is rejected when any above
operation fails.”h]”hX   First, the addresses of the patched functions are found according to their
names. The special relocations, mentioned in the section â€œNew functionsâ€,
are applied. The relevant entries are created under
/sys/kernel/livepatch/<name>. The patch is rejected when any above
operation fails.”…””}”(hjð  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h M>hjÑ  hžhubh¸)”}”(hXŸ  Second, livepatch enters into a transition state where tasks are converging
to the patched state. If an original function is patched for the first
time, a function specific struct klp_ops is created and an universal
ftrace handler is registered\ [#]_. This stage is indicated by a value of '1'
in /sys/kernel/livepatch/<name>/transition. For more information about
this process, see the "Consistency model" section.”h]”(hŒöSecond, livepatch enters into a transition state where tasks are converging
to the patched state. If an original function is patched for the first
time, a function specific struct klp_ops is created and an universal
ftrace handler is registered  ”…””}”(hjþ  hžhhŸNh NubhŒfootnote_reference”“”)”}”(hŒ[#]_”h]”hŒ1”…””}”(hj  hžhhŸNh Nubah}”(h]”Œid1”ah ]”h"]”h$]”h&]”Œauto”Kj!  Œid2”Œdocname”Œlivepatch/livepatch”uh1j  hjþ  Œresolved”KubhŒ­. This stage is indicated by a value of â€˜1â€™
in /sys/kernel/livepatch/<name>/transition. For more information about
this process, see the â€œConsistency modelâ€ section.”…””}”(hjþ  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h MDhjÑ  hžhubh¸)”}”(hŒQFinally, once all tasks have been patched, the 'transition' value changes
to '0'.”h]”hŒYFinally, once all tasks have been patched, the â€˜transitionâ€™ value changes
to â€˜0â€™.”…””}”(hj&  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h MKhjÑ  hžhubhŒfootnote”“”)”}”(hX	  Note that functions might be patched multiple times. The ftrace handler
is registered only once for a given function. Further patches just add
an entry to the list (see field `func_stack`) of the struct klp_ops.
The right implementation is selected by the ftrace handler, see
the "Consistency model" section.

That said, it is highly recommended to use cumulative livepatches
because they help keeping the consistency of all changes. In this case,
functions might be patched two times only during the transition period.

”h]”(hŒlabel”“”)”}”(hhh]”hŒ1”…””}”(hj<  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j:  hj6  hžhhŸNh Nubh¸)”}”(hX4  Note that functions might be patched multiple times. The ftrace handler
is registered only once for a given function. Further patches just add
an entry to the list (see field `func_stack`) of the struct klp_ops.
The right implementation is selected by the ftrace handler, see
the "Consistency model" section.”h]”(hŒ¯Note that functions might be patched multiple times. The ftrace handler
is registered only once for a given function. Further patches just add
an entry to the list (see field ”…””}”(hjI  hžhhŸNh NubhŒtitle_reference”“”)”}”(hŒ`func_stack`”h]”hŒ
func_stack”…””}”(hjS  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jQ  hjI  ubhŒ}) of the struct klp_ops.
The right implementation is selected by the ftrace handler, see
the â€œConsistency modelâ€ section.”…””}”(hjI  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h MPhj6  ubh¸)”}”(hŒÑThat said, it is highly recommended to use cumulative livepatches
because they help keeping the consistency of all changes. In this case,
functions might be patched two times only during the transition period.”h]”hŒÑThat said, it is highly recommended to use cumulative livepatches
because they help keeping the consistency of all changes. In this case,
functions might be patched two times only during the transition period.”…””}”(hjk  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h MVhj6  ubeh}”(h]”j  ah ]”h"]”Œ1”ah$]”h&]”j  aj  Kj  j  uh1j4  hŸh¶h MNhjÑ  hžhubeh}”(h]”j=  ah ]”h"]”Œ5.2. enabling”ah$]”h&]”uh1h¡hjb  hžhhŸh¶h M8ubh¢)”}”(hhh]”(h§)”}”(hŒ5.3. Replacing”h]”hŒ5.3. Replacing”…””}”(hjŠ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”j!  jY  uh1h¦hj‡  hžhhŸh¶h M\ubh¸)”}”(hŒ\All enabled patches might get replaced by a cumulative patch that
has the .replace flag set.”h]”hŒ\All enabled patches might get replaced by a cumulative patch that
has the .replace flag set.”…””}”(hj˜  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h M^hj‡  hžhubh¸)”}”(hXb  Once the new patch is enabled and the 'transition' finishes then
all the functions (struct klp_func) associated with the replaced
patches are removed from the corresponding struct klp_ops. Also
the ftrace handler is unregistered and the struct klp_ops is
freed when the related function is not modified by the new patch
and func_stack list becomes empty.”h]”hXf  Once the new patch is enabled and the â€˜transitionâ€™ finishes then
all the functions (struct klp_func) associated with the replaced
patches are removed from the corresponding struct klp_ops. Also
the ftrace handler is unregistered and the struct klp_ops is
freed when the related function is not modified by the new patch
and func_stack list becomes empty.”…””}”(hj¦  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Mahj‡  hžhubh¸)”}”(hŒDSee Documentation/livepatch/cumulative-patches.rst for more details.”h]”hŒDSee Documentation/livepatch/cumulative-patches.rst for more details.”…””}”(hj´  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Mhhj‡  hžhubeh}”(h]”j_  ah ]”h"]”Œ5.3. replacing”ah$]”h&]”uh1h¡hjb  hžhhŸh¶h M\ubh¢)”}”(hhh]”(h§)”}”(hŒ5.4. Disabling”h]”hŒ5.4. Disabling”…””}”(hjÌ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”j!  j{  uh1h¦hjÉ  hžhhŸh¶h Mlubh¸)”}”(hŒZEnabled patches might get disabled by writing '0' to
/sys/kernel/livepatch/<name>/enabled.”h]”hŒ^Enabled patches might get disabled by writing â€˜0â€™ to
/sys/kernel/livepatch/<name>/enabled.”…””}”(hjÚ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h MnhjÉ  hžhubh¸)”}”(hXj  First, livepatch enters into a transition state where tasks are converging
to the unpatched state. The system starts using either the code from
the previously enabled patch or even the original one. This stage is
indicated by a value of '1' in /sys/kernel/livepatch/<name>/transition.
For more information about this process, see the "Consistency model"
section.”h]”hXr  First, livepatch enters into a transition state where tasks are converging
to the unpatched state. The system starts using either the code from
the previously enabled patch or even the original one. This stage is
indicated by a value of â€˜1â€™ in /sys/kernel/livepatch/<name>/transition.
For more information about this process, see the â€œConsistency modelâ€
section.”…””}”(hjè  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h MqhjÉ  hžhubh¸)”}”(hX=  Second, once all tasks have been unpatched, the 'transition' value changes
to '0'. All the functions (struct klp_func) associated with the to-be-disabled
patch are removed from the corresponding struct klp_ops. The ftrace handler
is unregistered and the struct klp_ops is freed when the func_stack list
becomes empty.”h]”hXE  Second, once all tasks have been unpatched, the â€˜transitionâ€™ value changes
to â€˜0â€™. All the functions (struct klp_func) associated with the to-be-disabled
patch are removed from the corresponding struct klp_ops. The ftrace handler
is unregistered and the struct klp_ops is freed when the func_stack list
becomes empty.”…””}”(hjö  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h MxhjÉ  hžhubh¸)”}”(hŒ(Third, the sysfs interface is destroyed.”h]”hŒ(Third, the sysfs interface is destroyed.”…””}”(hj	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h M~hjÉ  hžhubeh}”(h]”j  ah ]”h"]”Œ5.4. disabling”ah$]”h&]”uh1h¡hjb  hžhhŸh¶h Mlubh¢)”}”(hhh]”(h§)”}”(hŒ5.5. Removing”h]”hŒ5.5. Removing”…””}”(hj	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”j!  j  uh1h¦hj	  hžhhŸh¶h M‚ubh¸)”}”(hXQ  Module removal is only safe when there are no users of functions provided
by the module. This is the reason why the force feature permanently
disables the removal. Only when the system is successfully transitioned
to a new patch state (patched/unpatched) without being forced it is
guaranteed that no task sleeps or runs in the old code.”h]”hXQ  Module removal is only safe when there are no users of functions provided
by the module. This is the reason why the force feature permanently
disables the removal. Only when the system is successfully transitioned
to a new patch state (patched/unpatched) without being forced it is
guaranteed that no task sleeps or runs in the old code.”…””}”(hj*	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h M„hj	  hžhubeh}”(h]”j£  ah ]”h"]”Œ5.5. removing”ah$]”h&]”uh1h¡hjb  hžhhŸh¶h M‚ubeh}”(h]”jü  ah ]”h"]”Œ5. livepatch life-cycle”ah$]”h&]”uh1h¡hh£hžhhŸh¶h M ubh¢)”}”(hhh]”(h§)”}”(hŒ6. Sysfs”h]”hŒ6. Sysfs”…””}”(hjI	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”j!  jË  uh1h¦hjF	  hžhhŸh¶h MŒubh¸)”}”(hŒŽInformation about the registered patches can be found under
/sys/kernel/livepatch. The patches could be enabled and disabled
by writing there.”h]”hŒŽInformation about the registered patches can be found under
/sys/kernel/livepatch. The patches could be enabled and disabled
by writing there.”…””}”(hjW	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h MŽhjF	  hžhubh¸)”}”(hŒb/sys/kernel/livepatch/<patch>/force attributes allow administrator to affect a
patching operation.”h]”hŒb/sys/kernel/livepatch/<patch>/force attributes allow administrator to affect a
patching operation.”…””}”(hje	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h M’hjF	  hžhubh¸)”}”(hŒFSee Documentation/ABI/testing/sysfs-kernel-livepatch for more details.”h]”hŒFSee Documentation/ABI/testing/sysfs-kernel-livepatch for more details.”…””}”(hjs	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h M•hjF	  hžhubeh}”(h]”jÑ  ah ]”h"]”Œ6. sysfs”ah$]”h&]”uh1h¡hh£hžhhŸh¶h MŒubh¢)”}”(hhh]”(h§)”}”(hŒ7. Limitations”h]”hŒ7. Limitations”…””}”(hj‹	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”j!  jí  uh1h¦hjˆ	  hžhhŸh¶h M™ubh¸)”}”(hŒ=The current Livepatch implementation has several limitations:”h]”hŒ=The current Livepatch implementation has several limitations:”…””}”(hj™	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h M›hjˆ	  hžhubjW  )”}”(hXˆ  - Only functions that can be traced could be patched.

  Livepatch is based on the dynamic ftrace. In particular, functions
  implementing ftrace or the livepatch ftrace handler could not be
  patched. Otherwise, the code would end up in an infinite loop. A
  potential mistake is prevented by marking the problematic functions
  by "notrace".


- Livepatch works reliably only when the dynamic ftrace is located at
  the very beginning of the function.

  The function need to be redirected before the stack or the function
  parameters are modified in any way. For example, livepatch requires
  using -fentry gcc compiler option on x86_64.

  One exception is the PPC port. It uses relative addressing and TOC.
  Each function has to handle TOC and save LR before it could call
  the ftrace handler. This operation has to be reverted on return.
  Fortunately, the generic ftrace code has the same problem and all
  this is handled on the ftrace level.


- Kretprobes using the ftrace framework conflict with the patched
  functions.

  Both kretprobes and livepatches use a ftrace handler that modifies
  the return address. The first user wins. Either the probe or the patch
  is rejected when the handler is already in use by the other.


- Kprobes in the original function are ignored when the code is
  redirected to the new implementation.

  There is a work in progress to add warnings about this situation.”h]”hß)”}”(hhh]”(hä)”}”(hXN  Only functions that can be traced could be patched.

Livepatch is based on the dynamic ftrace. In particular, functions
implementing ftrace or the livepatch ftrace handler could not be
patched. Otherwise, the code would end up in an infinite loop. A
potential mistake is prevented by marking the problematic functions
by "notrace".


”h]”(h¸)”}”(hŒ3Only functions that can be traced could be patched.”h]”hŒ3Only functions that can be traced could be patched.”…””}”(hj²	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Mhj®	  ubh¸)”}”(hX  Livepatch is based on the dynamic ftrace. In particular, functions
implementing ftrace or the livepatch ftrace handler could not be
patched. Otherwise, the code would end up in an infinite loop. A
potential mistake is prevented by marking the problematic functions
by "notrace".”h]”hX  Livepatch is based on the dynamic ftrace. In particular, functions
implementing ftrace or the livepatch ftrace handler could not be
patched. Otherwise, the code would end up in an infinite loop. A
potential mistake is prevented by marking the problematic functions
by â€œnotraceâ€.”…””}”(hjÀ	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h MŸhj®	  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hãhj«	  ubhä)”}”(hXM  Livepatch works reliably only when the dynamic ftrace is located at
the very beginning of the function.

The function need to be redirected before the stack or the function
parameters are modified in any way. For example, livepatch requires
using -fentry gcc compiler option on x86_64.

One exception is the PPC port. It uses relative addressing and TOC.
Each function has to handle TOC and save LR before it could call
the ftrace handler. This operation has to be reverted on return.
Fortunately, the generic ftrace code has the same problem and all
this is handled on the ftrace level.

”h]”(h¸)”}”(hŒgLivepatch works reliably only when the dynamic ftrace is located at
the very beginning of the function.”h]”hŒgLivepatch works reliably only when the dynamic ftrace is located at
the very beginning of the function.”…””}”(hjØ	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h M§hjÔ	  ubh¸)”}”(hŒ´The function need to be redirected before the stack or the function
parameters are modified in any way. For example, livepatch requires
using -fentry gcc compiler option on x86_64.”h]”hŒ´The function need to be redirected before the stack or the function
parameters are modified in any way. For example, livepatch requires
using -fentry gcc compiler option on x86_64.”…””}”(hjæ	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h MªhjÔ	  ubh¸)”}”(hX,  One exception is the PPC port. It uses relative addressing and TOC.
Each function has to handle TOC and save LR before it could call
the ftrace handler. This operation has to be reverted on return.
Fortunately, the generic ftrace code has the same problem and all
this is handled on the ftrace level.”h]”hX,  One exception is the PPC port. It uses relative addressing and TOC.
Each function has to handle TOC and save LR before it could call
the ftrace handler. This operation has to be reverted on return.
Fortunately, the generic ftrace code has the same problem and all
this is handled on the ftrace level.”…””}”(hjô	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h M®hjÔ	  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hãhj«	  ubhä)”}”(hX  Kretprobes using the ftrace framework conflict with the patched
functions.

Both kretprobes and livepatches use a ftrace handler that modifies
the return address. The first user wins. Either the probe or the patch
is rejected when the handler is already in use by the other.

”h]”(h¸)”}”(hŒJKretprobes using the ftrace framework conflict with the patched
functions.”h]”hŒJKretprobes using the ftrace framework conflict with the patched
functions.”…””}”(hj
  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Mµhj
  ub•*      h¸)”}”(hŒÆBoth kretprobes and livepatches use a ftrace handler that modifies
the return address. The first user wins. Either the probe or the patch
is rejected when the handler is already in use by the other.”h]”hŒÆBoth kretprobes and livepatches use a ftrace handler that modifies
the return address. The first user wins. Either the probe or the patch
is rejected when the handler is already in use by the other.”…””}”(hj
  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h M¸hj
  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hãhj«	  ubhä)”}”(hŒ¦Kprobes in the original function are ignored when the code is
redirected to the new implementation.

There is a work in progress to add warnings about this situation.”h]”(h¸)”}”(hŒcKprobes in the original function are ignored when the code is
redirected to the new implementation.”h]”hŒcKprobes in the original function are ignored when the code is
redirected to the new implementation.”…””}”(hj2
  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h M½hj.
  ubh¸)”}”(hŒAThere is a work in progress to add warnings about this situation.”h]”hŒAThere is a work in progress to add warnings about this situation.”…””}”(hj@
  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h MÀhj.
  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hãhj«	  ubeh}”(h]”h ]”h"]”h$]”h&]”j­  j®  uh1hÞhŸh¶h Mhj§	  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jV  hŸh¶h Mhjˆ	  hžhubeh}”(h]”jó  ah ]”h"]”Œ7. limitations”ah$]”h&]”uh1h¡hh£hžhhŸh¶h M™ubeh}”(h]”Œ	livepatch”ah ]”h"]”Œ	livepatch”ah$]”h&]”uh1h¡hhhžhhŸh¶h Kubeh}”(h]”h ]”h"]”h$]”h&]”Œsource”h¶uh1hŒcurrent_source”NŒcurrent_line”NŒsettings”Œdocutils.frontend”ŒValues”“”)”}”(h¦NŒ	generator”NŒ	datestamp”NŒsource_link”NŒ
source_url”NŒtoc_backlinks”Œentry”Œfootnote_backlinks”KŒsectnum_xform”KŒstrip_comments”NŒstrip_elements_with_classes”NŒstrip_classes”NŒreport_level”KŒ
halt_level”KŒexit_status_level”KŒdebug”NŒwarning_stream”NŒ	traceback”ˆŒinput_encoding”Œ	utf-8-sig”Œinput_encoding_error_handler”Œstrict”Œoutput_encoding”Œutf-8”Œoutput_encoding_error_handler”j’
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