Based on kernel version 4.8. Page generated on 2016-10-06 23:19 EST.
1 Undefined Behavior Sanitizer - UBSAN 2 3 Overview 4 -------- 5 6 UBSAN is a runtime undefined behaviour checker. 7 8 UBSAN uses compile-time instrumentation to catch undefined behavior (UB). 9 Compiler inserts code that perform certain kinds of checks before operations 10 that may cause UB. If check fails (i.e. UB detected) __ubsan_handle_* 11 function called to print error message. 12 13 GCC has that feature since 4.9.x [1] (see -fsanitize=undefined option and 14 its suboptions). GCC 5.x has more checkers implemented [2]. 15 16 Report example 17 --------------- 18 19 ================================================================================ 20 UBSAN: Undefined behaviour in ../include/linux/bitops.h:110:33 21 shift exponent 32 is to large for 32-bit type 'unsigned int' 22 CPU: 0 PID: 0 Comm: swapper Not tainted 4.4.0-rc1+ #26 23 0000000000000000 ffffffff82403cc8 ffffffff815e6cd6 0000000000000001 24 ffffffff82403cf8 ffffffff82403ce0 ffffffff8163a5ed 0000000000000020 25 ffffffff82403d78 ffffffff8163ac2b ffffffff815f0001 0000000000000002 26 Call Trace: 27 [<ffffffff815e6cd6>] dump_stack+0x45/0x5f 28 [<ffffffff8163a5ed>] ubsan_epilogue+0xd/0x40 29 [<ffffffff8163ac2b>] __ubsan_handle_shift_out_of_bounds+0xeb/0x130 30 [<ffffffff815f0001>] ? radix_tree_gang_lookup_slot+0x51/0x150 31 [<ffffffff8173c586>] _mix_pool_bytes+0x1e6/0x480 32 [<ffffffff83105653>] ? dmi_walk_early+0x48/0x5c 33 [<ffffffff8173c881>] add_device_randomness+0x61/0x130 34 [<ffffffff83105b35>] ? dmi_save_one_device+0xaa/0xaa 35 [<ffffffff83105653>] dmi_walk_early+0x48/0x5c 36 [<ffffffff831066ae>] dmi_scan_machine+0x278/0x4b4 37 [<ffffffff8111d58a>] ? vprintk_default+0x1a/0x20 38 [<ffffffff830ad120>] ? early_idt_handler_array+0x120/0x120 39 [<ffffffff830b2240>] setup_arch+0x405/0xc2c 40 [<ffffffff830ad120>] ? early_idt_handler_array+0x120/0x120 41 [<ffffffff830ae053>] start_kernel+0x83/0x49a 42 [<ffffffff830ad120>] ? early_idt_handler_array+0x120/0x120 43 [<ffffffff830ad386>] x86_64_start_reservations+0x2a/0x2c 44 [<ffffffff830ad4f3>] x86_64_start_kernel+0x16b/0x17a 45 ================================================================================ 46 47 Usage 48 ----- 49 50 To enable UBSAN configure kernel with: 51 52 CONFIG_UBSAN=y 53 54 and to check the entire kernel: 55 56 CONFIG_UBSAN_SANITIZE_ALL=y 57 58 To enable instrumentation for specific files or directories, add a line 59 similar to the following to the respective kernel Makefile: 60 61 For a single file (e.g. main.o): 62 UBSAN_SANITIZE_main.o := y 63 64 For all files in one directory: 65 UBSAN_SANITIZE := y 66 67 To exclude files from being instrumented even if 68 CONFIG_UBSAN_SANITIZE_ALL=y, use: 69 70 UBSAN_SANITIZE_main.o := n 71 and: 72 UBSAN_SANITIZE := n 73 74 Detection of unaligned accesses controlled through the separate option - 75 CONFIG_UBSAN_ALIGNMENT. It's off by default on architectures that support 76 unaligned accesses (CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS=y). One could 77 still enable it in config, just note that it will produce a lot of UBSAN 78 reports. 79 80 References 81 ---------- 82 83 [1] - https://gcc.gnu.org/onlinedocs/gcc-4.9.0/gcc/Debugging-Options.html 84 [2] - https://gcc.gnu.org/onlinedocs/gcc/Debugging-Options.html
