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diff --git a/Documentation/ubsan.txt b/Documentation/ubsan.txt new file mode 100644 index 000000000000..f58215ef5797 --- /dev/null +++ b/Documentation/ubsan.txt @@ -0,0 +1,84 @@ +Undefined Behavior Sanitizer - UBSAN + +Overview +-------- + +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: + [<ffffffff815e6cd6>] dump_stack+0x45/0x5f + [<ffffffff8163a5ed>] ubsan_epilogue+0xd/0x40 + [<ffffffff8163ac2b>] __ubsan_handle_shift_out_of_bounds+0xeb/0x130 + [<ffffffff815f0001>] ? radix_tree_gang_lookup_slot+0x51/0x150 + [<ffffffff8173c586>] _mix_pool_bytes+0x1e6/0x480 + [<ffffffff83105653>] ? dmi_walk_early+0x48/0x5c + [<ffffffff8173c881>] add_device_randomness+0x61/0x130 + [<ffffffff83105b35>] ? dmi_save_one_device+0xaa/0xaa + [<ffffffff83105653>] dmi_walk_early+0x48/0x5c + [<ffffffff831066ae>] dmi_scan_machine+0x278/0x4b4 + [<ffffffff8111d58a>] ? vprintk_default+0x1a/0x20 + [<ffffffff830ad120>] ? early_idt_handler_array+0x120/0x120 + [<ffffffff830b2240>] setup_arch+0x405/0xc2c + [<ffffffff830ad120>] ? early_idt_handler_array+0x120/0x120 + [<ffffffff830ae053>] start_kernel+0x83/0x49a + [<ffffffff830ad120>] ? early_idt_handler_array+0x120/0x120 + [<ffffffff830ad386>] x86_64_start_reservations+0x2a/0x2c + [<ffffffff830ad4f3>] 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 |