From: Zachary Amsden Privilege checking cleanup. Originally, these diffs were much greater, but recent cleanups in Linux have already done much of the cleanup. I added some explanatory comments in places where the reasoning behind certain tests is rather subtle. Also, in traps.c, we can skip the user_mode check in handle_BUG(). The reason is, there are only two call chains - one via die_if_kernel() and one via do_page_fault(), both entering from die(). Both of these paths already ensure that a kernel mode failure has happened. Also, the original check here, if (user_mode(regs)) was insufficient anyways, since it would not rule out BUG faults from V8086 mode execution. Saving the %ss segment in show_regs() rather than assuming a fixed value also gives better information about the current kernel state in the register dump. Signed-off-by: Zachary Amsden Signed-off-by: Andrew Morton --- arch/i386/kernel/signal.c | 4 +++- arch/i386/kernel/traps.c | 5 +---- include/asm-i386/ptrace.h | 7 +++++++ 3 files changed, 11 insertions(+), 5 deletions(-) diff -puN arch/i386/kernel/signal.c~x86-privilege-cleanup arch/i386/kernel/signal.c --- devel/arch/i386/kernel/signal.c~x86-privilege-cleanup 2005-08-03 23:08:12.000000000 -0700 +++ devel-akpm/arch/i386/kernel/signal.c 2005-08-03 23:08:12.000000000 -0700 @@ -603,7 +603,9 @@ int fastcall do_signal(struct pt_regs *r * We want the common case to go fast, which * is why we may in certain cases get here from * kernel mode. Just return without doing anything - * if so. + * if so. vm86 regs switched out by assembly code + * before reaching here, so testing against kernel + * CS suffices. */ if (!user_mode(regs)) return 1; diff -puN arch/i386/kernel/traps.c~x86-privilege-cleanup arch/i386/kernel/traps.c --- devel/arch/i386/kernel/traps.c~x86-privilege-cleanup 2005-08-03 23:08:12.000000000 -0700 +++ devel-akpm/arch/i386/kernel/traps.c 2005-08-03 23:08:12.000000000 -0700 @@ -210,7 +210,7 @@ void show_registers(struct pt_regs *regs unsigned short ss; esp = (unsigned long) (®s->esp); - ss = __KERNEL_DS; + savesegment(ss, ss); if (user_mode(regs)) { in_kernel = 0; esp = regs->esp; @@ -267,9 +267,6 @@ static void handle_BUG(struct pt_regs *r char c; unsigned long eip; - if (user_mode(regs)) - goto no_bug; /* Not in kernel */ - eip = regs->eip; if (eip < PAGE_OFFSET) diff -puN include/asm-i386/ptrace.h~x86-privilege-cleanup include/asm-i386/ptrace.h --- devel/include/asm-i386/ptrace.h~x86-privilege-cleanup 2005-08-03 23:08:12.000000000 -0700 +++ devel-akpm/include/asm-i386/ptrace.h 2005-08-03 23:08:12.000000000 -0700 @@ -61,6 +61,13 @@ struct pt_regs { struct task_struct; extern void send_sigtrap(struct task_struct *tsk, struct pt_regs *regs, int error_code); +/* + * user_mode_vm(regs) determines whether a register set came from user mode. + * This is true if V8086 mode was enabled OR if the register set was from + * protected mode with RPL-3 CS value. This tricky test checks that with + * one comparison. Many places in the kernel can bypass this full check + * if they have already ruled out V8086 mode, so user_mode(regs) can be used. + */ static inline int user_mode(struct pt_regs *regs) { return (regs->xcs & 3) != 0; _