1.. SPDX-License-Identifier: GPL-2.0 2 3Undefined Behavior Sanitizer - UBSAN 4==================================== 5 6UBSAN is a runtime undefined behaviour checker. 7 8UBSAN uses compile-time instrumentation to catch undefined behavior (UB). 9Compiler inserts code that perform certain kinds of checks before operations 10that may cause UB. If check fails (i.e. UB detected) __ubsan_handle_* 11function called to print error message. 12 13GCC has that feature since 4.9.x [1_] (see ``-fsanitize=undefined`` option and 14its suboptions). GCC 5.x has more checkers implemented [2_]. 15 16Report example 17-------------- 18 19:: 20 21 ================================================================================ 22 UBSAN: Undefined behaviour in ../include/linux/bitops.h:110:33 23 shift exponent 32 is to large for 32-bit type 'unsigned int' 24 CPU: 0 PID: 0 Comm: swapper Not tainted 4.4.0-rc1+ #26 25 0000000000000000 ffffffff82403cc8 ffffffff815e6cd6 0000000000000001 26 ffffffff82403cf8 ffffffff82403ce0 ffffffff8163a5ed 0000000000000020 27 ffffffff82403d78 ffffffff8163ac2b ffffffff815f0001 0000000000000002 28 Call Trace: 29 [<ffffffff815e6cd6>] dump_stack+0x45/0x5f 30 [<ffffffff8163a5ed>] ubsan_epilogue+0xd/0x40 31 [<ffffffff8163ac2b>] __ubsan_handle_shift_out_of_bounds+0xeb/0x130 32 [<ffffffff815f0001>] ? radix_tree_gang_lookup_slot+0x51/0x150 33 [<ffffffff8173c586>] _mix_pool_bytes+0x1e6/0x480 34 [<ffffffff83105653>] ? dmi_walk_early+0x48/0x5c 35 [<ffffffff8173c881>] add_device_randomness+0x61/0x130 36 [<ffffffff83105b35>] ? dmi_save_one_device+0xaa/0xaa 37 [<ffffffff83105653>] dmi_walk_early+0x48/0x5c 38 [<ffffffff831066ae>] dmi_scan_machine+0x278/0x4b4 39 [<ffffffff8111d58a>] ? vprintk_default+0x1a/0x20 40 [<ffffffff830ad120>] ? early_idt_handler_array+0x120/0x120 41 [<ffffffff830b2240>] setup_arch+0x405/0xc2c 42 [<ffffffff830ad120>] ? early_idt_handler_array+0x120/0x120 43 [<ffffffff830ae053>] start_kernel+0x83/0x49a 44 [<ffffffff830ad120>] ? early_idt_handler_array+0x120/0x120 45 [<ffffffff830ad386>] x86_64_start_reservations+0x2a/0x2c 46 [<ffffffff830ad4f3>] x86_64_start_kernel+0x16b/0x17a 47 ================================================================================ 48 49Usage 50----- 51 52To enable UBSAN configure kernel with:: 53 54 CONFIG_UBSAN=y 55 56and to check the entire kernel:: 57 58 CONFIG_UBSAN_SANITIZE_ALL=y 59 60To enable instrumentation for specific files or directories, add a line 61similar to the following to the respective kernel Makefile: 62 63- For a single file (e.g. main.o):: 64 65 UBSAN_SANITIZE_main.o := y 66 67- For all files in one directory:: 68 69 UBSAN_SANITIZE := y 70 71To exclude files from being instrumented even if 72``CONFIG_UBSAN_SANITIZE_ALL=y``, use:: 73 74 UBSAN_SANITIZE_main.o := n 75 76and:: 77 78 UBSAN_SANITIZE := n 79 80Detection of unaligned accesses controlled through the separate option - 81CONFIG_UBSAN_ALIGNMENT. It's off by default on architectures that support 82unaligned accesses (CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS=y). One could 83still enable it in config, just note that it will produce a lot of UBSAN 84reports. 85 86References 87---------- 88 89.. _1: https://gcc.gnu.org/onlinedocs/gcc-4.9.0/gcc/Debugging-Options.html 90.. _2: https://gcc.gnu.org/onlinedocs/gcc/Debugging-Options.html 91.. _3: https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html 92