1 .. SPDX-License-Identifier: GPL-2.0
3 Undefined Behavior Sanitizer - UBSAN
4 ====================================
6 UBSAN is a runtime undefined behaviour checker.
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.
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_].
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
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 ================================================================================
52 To enable UBSAN configure kernel with::
56 and to check the entire kernel::
58 CONFIG_UBSAN_SANITIZE_ALL=y
60 To enable instrumentation for specific files or directories, add a line
61 similar to the following to the respective kernel Makefile:
63 - For a single file (e.g. main.o)::
65 UBSAN_SANITIZE_main.o := y
67 - For all files in one directory::
71 To exclude files from being instrumented even if
72 ``CONFIG_UBSAN_SANITIZE_ALL=y``, use::
74 UBSAN_SANITIZE_main.o := n
80 Detection of unaligned accesses controlled through the separate option -
81 CONFIG_UBSAN_ALIGNMENT. It's off by default on architectures that support
82 unaligned accesses (CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS=y). One could
83 still enable it in config, just note that it will produce a lot of UBSAN
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