Use a relative address in .note.crashpad.info

The desc value in the note is now the offset of CRASHPAD_INFO_SYMBOL
from desc.

Making this note writable can trigger a linker error resulting in
the binary embedding .note.crashpad.info to be rejected by the
kernel during program loading.

The error was observed with:
GNU ld (GNU Binutils for Debian) 2.30
clang version 4.0.1-10 (tags/RELEASE_401/final)
Debian 4.17.17-1rodete2

When the note is made writable, crashpad_snapshot_test contains two
PT_LOAD segments which map to the same page.

LOAD         0x0000000000000000 0x0000000000000000 0x0000000000000000
             0x0000000000000258 0x0000000000000258  R      0x200000
LOAD         0x0000000000000258 0x0000000000000258 0x0000000000000258
             0x00000000002b84d8 0x00000000002b8950  RWE    0x200000

Executing this binary with the execv system call triggers a segfault
during program loading (an error can't be returned because the original
process vm has already been discarded).

I suspect (I haven't set up a debuggable kernel) the failure occurs
while attempting to map the second load segment because its virtual
address, 0x258, is in the same page as the first load segment.
https://elixir.bootlin.com/linux/v4.17.17/source/fs/binfmt_elf.c#L380

The linker normally produces consecutive load segments where the second
segment is loaded 0x200000 bytes after the first, which I think is the
maximum expected page size. Modifying the test executable to load the
second segment at 0x1258 (4096 byte page size) allows program loading
to succeed (but of course crashes after control is given to it).

Bug: crashpad:260
Change-Id: I2b9f1e66e98919138baef3da991a9710bd970dc4
Reviewed-on: https://chromium-review.googlesource.com/c/1292232
Reviewed-by: Scott Graham <scottmg@chromium.org>
Reviewed-by: Mark Mentovai <mark@chromium.org>
Commit-Queue: Joshua Peraza <jperaza@chromium.org>
7 files changed
tree: 21c913dcda9ff5868179b5236f7f19444d9c08b8
  1. .clang-format
  2. .gitignore
  3. .gn
  4. .vpython
  5. AUTHORS
  6. BUILD.gn
  7. CONTRIBUTORS
  8. DEPS
  9. LICENSE
  10. README.md
  11. build/
  12. client/
  13. codereview.settings
  14. compat/
  15. crashpad.gyp
  16. doc/
  17. handler/
  18. infra/
  19. minidump/
  20. navbar.md
  21. package.h
  22. snapshot/
  23. test/
  24. third_party/
  25. tools/
  26. util/
README.md

Crashpad

Crashpad is a crash-reporting system.

Documentation

Source Code

Crashpad’s source code is hosted in a Git repository at https://chromium.googlesource.com/crashpad/crashpad.

Other Links