Commit | Line | Data |
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1ead009c JC |
1 | The Undefined Behavior Sanitizer - UBSAN |
2 | ======================================== | |
c6d30853 AR |
3 | |
4 | UBSAN is a runtime undefined behaviour checker. | |
5 | ||
6 | UBSAN uses compile-time instrumentation to catch undefined behavior (UB). | |
7 | Compiler inserts code that perform certain kinds of checks before operations | |
8 | that may cause UB. If check fails (i.e. UB detected) __ubsan_handle_* | |
9 | function called to print error message. | |
10 | ||
1ead009c JC |
11 | GCC has that feature since 4.9.x [1_] (see ``-fsanitize=undefined`` option and |
12 | its suboptions). GCC 5.x has more checkers implemented [2_]. | |
c6d30853 AR |
13 | |
14 | Report example | |
1ead009c JC |
15 | -------------- |
16 | ||
17 | :: | |
c6d30853 AR |
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 | ||
1ead009c | 50 | To enable UBSAN configure kernel with:: |
c6d30853 AR |
51 | |
52 | CONFIG_UBSAN=y | |
53 | ||
1ead009c | 54 | and to check the entire kernel:: |
c6d30853 AR |
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 | ||
1ead009c JC |
61 | - For a single file (e.g. main.o):: |
62 | ||
63 | UBSAN_SANITIZE_main.o := y | |
c6d30853 | 64 | |
1ead009c JC |
65 | - For all files in one directory:: |
66 | ||
67 | UBSAN_SANITIZE := y | |
c6d30853 AR |
68 | |
69 | To exclude files from being instrumented even if | |
1ead009c JC |
70 | ``CONFIG_UBSAN_SANITIZE_ALL=y``, use:: |
71 | ||
72 | UBSAN_SANITIZE_main.o := n | |
73 | ||
74 | and:: | |
c6d30853 | 75 | |
1ead009c | 76 | UBSAN_SANITIZE := n |
c6d30853 AR |
77 | |
78 | Detection of unaligned accesses controlled through the separate option - | |
79 | CONFIG_UBSAN_ALIGNMENT. It's off by default on architectures that support | |
80 | unaligned accesses (CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS=y). One could | |
81 | still enable it in config, just note that it will produce a lot of UBSAN | |
82 | reports. | |
83 | ||
84 | References | |
85 | ---------- | |
86 | ||
1ead009c JC |
87 | .. _1: https://gcc.gnu.org/onlinedocs/gcc-4.9.0/gcc/Debugging-Options.html |
88 | .. _2: https://gcc.gnu.org/onlinedocs/gcc/Debugging-Options.html |