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[Scudo] Use GWP-ASan's aligned allocations and fixup postalloc hooks.

Authored by hctim on Apr 23 2021, 9:47 AM.

Description

[Scudo] Use GWP-ASan's aligned allocations and fixup postalloc hooks.

This patch does a few cleanup things:

  1. The non-standalone scudo has a problem where GWP-ASan allocations may not meet alignment requirements where Scudo was requested to have alignment >= 16. Use the new GWP-ASan API to fix this.
  2. The standalone variant loses some debugging information inside of GWP-ASan because we ask GWP-ASan to allocate an aligned size in the frontend. This means reports end up with 'UaF on a 16-byte allocation' for a 1-byte allocation with 16-byte alignment. Also use the new API to fix this.
  3. Add post-alloc hooks for GWP-ASan intercepted allocations, and add stats tracking for GWP-ASan allocations.
  4. Add a small test that checks the alignment of the frontend allocator, so that it can be used under GWP-ASan torture mode.
  5. Add GWP-ASan torture mode as a testing configuration to catch these regressions.

Depends on D94830, D95889.

Reviewed By: cryptoad

Differential Revision: https://reviews.llvm.org/D95884