The Undefined Behavior Sanitizer - UBSAN ======================================== UBSAN is a runtime undefined behaviour checker. UBSAN uses compile-time instrumentation to catch undefined behavior (UB). Compiler inserts code that perform certain kinds of checks before operations that may cause UB. If check fails (i.e. UB detected) __ubsan_handle_* function called to print error message. GCC has that feature since 4.9.x [1_] (see ``-fsanitize=undefined`` option and its suboptions). GCC 5.x has more checkers implemented [2_]. Report example -------------- :: ================================================================================ UBSAN: Undefined behaviour in ../include/linux/bitops.h:110:33 shift exponent 32 is to large for 32-bit type 'unsigned int' CPU: 0 PID: 0 Comm: swapper Not tainted 4.4.0-rc1+ #26 0000000000000000 ffffffff82403cc8 ffffffff815e6cd6 0000000000000001 ffffffff82403cf8 ffffffff82403ce0 ffffffff8163a5ed 0000000000000020 ffffffff82403d78 ffffffff8163ac2b ffffffff815f0001 0000000000000002 Call Trace: [] dump_stack+0x45/0x5f [] ubsan_epilogue+0xd/0x40 [] __ubsan_handle_shift_out_of_bounds+0xeb/0x130 [] ? radix_tree_gang_lookup_slot+0x51/0x150 [] _mix_pool_bytes+0x1e6/0x480 [] ? dmi_walk_early+0x48/0x5c [] add_device_randomness+0x61/0x130 [] ? dmi_save_one_device+0xaa/0xaa [] dmi_walk_early+0x48/0x5c [] dmi_scan_machine+0x278/0x4b4 [] ? vprintk_default+0x1a/0x20 [] ? early_idt_handler_array+0x120/0x120 [] setup_arch+0x405/0xc2c [] ? early_idt_handler_array+0x120/0x120 [] start_kernel+0x83/0x49a [] ? early_idt_handler_array+0x120/0x120 [] x86_64_start_reservations+0x2a/0x2c [] x86_64_start_kernel+0x16b/0x17a ================================================================================ Usage ----- To enable UBSAN configure kernel with:: CONFIG_UBSAN=y and to check the entire kernel:: CONFIG_UBSAN_SANITIZE_ALL=y To enable instrumentation for specific files or directories, add a line similar to the following to the respective kernel Makefile: - For a single file (e.g. main.o):: UBSAN_SANITIZE_main.o := y - For all files in one directory:: UBSAN_SANITIZE := y To exclude files from being instrumented even if ``CONFIG_UBSAN_SANITIZE_ALL=y``, use:: UBSAN_SANITIZE_main.o := n and:: UBSAN_SANITIZE := n Detection of unaligned accesses controlled through the separate option - CONFIG_UBSAN_ALIGNMENT. It's off by default on architectures that support unaligned accesses (CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS=y). One could still enable it in config, just note that it will produce a lot of UBSAN reports. References ---------- .. _1: https://gcc.gnu.org/onlinedocs/gcc-4.9.0/gcc/Debugging-Options.html .. _2: https://gcc.gnu.org/onlinedocs/gcc/Debugging-Options.html