| Andrey Ryabinin | c6d3085 | 2016-01-20 15:00:55 -0800 | [diff] [blame] | 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 |