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llvm / llvm-project / 3b3f8c50b646600dc1846c7d3d018fdb39fbfe0b
commit3b3f8c50b646600dc1846c7d3d018fdb39fbfe0b[log] [tgz]
authorThurston Dang <thurston@google.com>Thu Mar 20 08:02:48 2025 -0700
committerGitHub <noreply@github.com>Thu Mar 20 08:02:48 2025 -0700
tree898909f8a864b10a4b0c984d83d88028df94af82
parentfdeb2ff30407afbfc3596aaf417a2a91cdff20c9 [diff]
[asan] Re-exec without ASLR if needed on 32-bit Linux (#131975)

High-entropy ASLR allows up to 16-bits of entropy (2**16 4KB pages ==
256MB; a bit more in practice because of implementation details), which
is a significant chunk of the user address space on 32-bit systems (4GB
or less). This, combined with ASan's shadow (512MB) and ASan's fixed
shadow offset (512MB), makes it possible for large binaries to fail to
map the shadow.

This patch changes ASan to do a one-time re-exec without ASLR if it
cannot map the shadow, thus reclaiming the ~256MB of address space.

Alternatives considered:
1) We don't lower ASan's fixed shadow offset, because that would limit
non-PIE binaries.
2) We don't switch to a dynamic shadow offset, because ASan for 32-bit
Linux relies on the compile-time constant offset to optimize its
instrumentation and compiler-rt.

This is loosely inspired by
https://github.com/llvm/llvm-project/pull/78351,
https://github.com/llvm/llvm-project/pull/85142, and
https://github.com/llvm/llvm-project/pull/85674, though those were
required because there were no static shadow mappings that could fully
shadow the range of user mappings; this is not the case for ASan.
5 files changed
tree: 898909f8a864b10a4b0c984d83d88028df94af82
  1. .ci/
  2. .github/
  3. bolt/
  4. clang/
  5. clang-tools-extra/
  6. cmake/
  7. compiler-rt/
  8. cross-project-tests/
  9. flang/
  10. flang-rt/
  11. libc/
  12. libclc/
  13. libcxx/
  14. libcxxabi/
  15. libunwind/
  16. lld/
  17. lldb/
  18. llvm/
  19. llvm-libgcc/
  20. mlir/
  21. offload/
  22. openmp/
  23. polly/
  24. pstl/
  25. runtimes/
  26. third-party/
  27. utils/
  28. .clang-format
  29. .clang-tidy
  30. .git-blame-ignore-revs
  31. .gitattributes
  32. .gitignore
  33. .mailmap
  34. CODE_OF_CONDUCT.md
  35. CONTRIBUTING.md
  36. LICENSE.TXT
  37. pyproject.toml
  38. README.md
  39. SECURITY.md
README.md

The LLVM Compiler Infrastructure

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Welcome to the LLVM project!

This repository contains the source code for LLVM, a toolkit for the construction of highly optimized compilers, optimizers, and run-time environments.

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