LXR linux/Documentation/ubsan.txt

   1Undefined Behavior Sanitizer - UBSAN
   2
   3Overview
   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         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
  47Usage
  48-----
  49
  50To enable UBSAN configure kernel with:
  51
  52        CONFIG_UBSAN=y
  53
  54and to check the entire kernel:
  55
  56        CONFIG_UBSAN_SANITIZE_ALL=y
  57
  58To enable instrumentation for specific files or directories, add a line
  59similar 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
  67To exclude files from being instrumented even if
  68CONFIG_UBSAN_SANITIZE_ALL=y, use:
  69
  70                UBSAN_SANITIZE_main.o := n
  71        and:
  72                UBSAN_SANITIZE := n
  73
  74Detection of unaligned accesses controlled through the separate option -
  75CONFIG_UBSAN_ALIGNMENT. It's off by default on architectures that support
  76unaligned accesses (CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS=y). One could
  77still enable it in config, just note that it will produce a lot of UBSAN
  78reports.
  79
  80References
  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
  85