ubsan.rst 3.2 KB

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  1. The Undefined Behavior Sanitizer - UBSAN
  2. ========================================
  3. UBSAN is a runtime undefined behaviour checker.
  4. UBSAN uses compile-time instrumentation to catch undefined behavior (UB).
  5. Compiler inserts code that perform certain kinds of checks before operations
  6. that may cause UB. If check fails (i.e. UB detected) __ubsan_handle_*
  7. function called to print error message.
  8. GCC has that feature since 4.9.x [1_] (see ``-fsanitize=undefined`` option and
  9. its suboptions). GCC 5.x has more checkers implemented [2_].
  10. Report example
  11. --------------
  12. ::
  13. ================================================================================
  14. UBSAN: Undefined behaviour in ../include/linux/bitops.h:110:33
  15. shift exponent 32 is to large for 32-bit type 'unsigned int'
  16. CPU: 0 PID: 0 Comm: swapper Not tainted 4.4.0-rc1+ #26
  17. 0000000000000000 ffffffff82403cc8 ffffffff815e6cd6 0000000000000001
  18. ffffffff82403cf8 ffffffff82403ce0 ffffffff8163a5ed 0000000000000020
  19. ffffffff82403d78 ffffffff8163ac2b ffffffff815f0001 0000000000000002
  20. Call Trace:
  21. [<ffffffff815e6cd6>] dump_stack+0x45/0x5f
  22. [<ffffffff8163a5ed>] ubsan_epilogue+0xd/0x40
  23. [<ffffffff8163ac2b>] __ubsan_handle_shift_out_of_bounds+0xeb/0x130
  24. [<ffffffff815f0001>] ? radix_tree_gang_lookup_slot+0x51/0x150
  25. [<ffffffff8173c586>] _mix_pool_bytes+0x1e6/0x480
  26. [<ffffffff83105653>] ? dmi_walk_early+0x48/0x5c
  27. [<ffffffff8173c881>] add_device_randomness+0x61/0x130
  28. [<ffffffff83105b35>] ? dmi_save_one_device+0xaa/0xaa
  29. [<ffffffff83105653>] dmi_walk_early+0x48/0x5c
  30. [<ffffffff831066ae>] dmi_scan_machine+0x278/0x4b4
  31. [<ffffffff8111d58a>] ? vprintk_default+0x1a/0x20
  32. [<ffffffff830ad120>] ? early_idt_handler_array+0x120/0x120
  33. [<ffffffff830b2240>] setup_arch+0x405/0xc2c
  34. [<ffffffff830ad120>] ? early_idt_handler_array+0x120/0x120
  35. [<ffffffff830ae053>] start_kernel+0x83/0x49a
  36. [<ffffffff830ad120>] ? early_idt_handler_array+0x120/0x120
  37. [<ffffffff830ad386>] x86_64_start_reservations+0x2a/0x2c
  38. [<ffffffff830ad4f3>] x86_64_start_kernel+0x16b/0x17a
  39. ================================================================================
  40. Usage
  41. -----
  42. To enable UBSAN configure kernel with::
  43. CONFIG_UBSAN=y
  44. and to check the entire kernel::
  45. CONFIG_UBSAN_SANITIZE_ALL=y
  46. To enable instrumentation for specific files or directories, add a line
  47. similar to the following to the respective kernel Makefile:
  48. - For a single file (e.g. main.o)::
  49. UBSAN_SANITIZE_main.o := y
  50. - For all files in one directory::
  51. UBSAN_SANITIZE := y
  52. To exclude files from being instrumented even if
  53. ``CONFIG_UBSAN_SANITIZE_ALL=y``, use::
  54. UBSAN_SANITIZE_main.o := n
  55. and::
  56. UBSAN_SANITIZE := n
  57. Detection of unaligned accesses controlled through the separate option -
  58. CONFIG_UBSAN_ALIGNMENT. It's off by default on architectures that support
  59. unaligned accesses (CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS=y). One could
  60. still enable it in config, just note that it will produce a lot of UBSAN
  61. reports.
  62. References
  63. ----------
  64. .. _1: https://gcc.gnu.org/onlinedocs/gcc-4.9.0/gcc/Debugging-Options.html
  65. .. _2: https://gcc.gnu.org/onlinedocs/gcc/Debugging-Options.html
  66. .. _3: https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html