[PATCH] D63360: hwasan: Use bits [3..11) of the ring buffer entry address as the base stack tag.

[Peter Collingbourne via Phabricator via llvm-commits]

pcc marked 2 inline comments as done.
pcc added inline comments.


================
Comment at: compiler-rt/test/hwasan/TestCases/random-align-right.c:30
 // CHECK1: accessing p[20]
+// CHECK1: accessing p[20]
 // CHECK1-NEXT: HWAddressSanitizer: tag-mismatch
----------------
eugenis wrote:
> why did you copy this line?
Because the additional call to GenerateRandomTag in InitRandomState causes the values that we assign to tail_magic in HwasanAllocatorInit to change in such a way that we catch the second bad access and not the first one. Without copying this line the `CHECK?-NEXT` lines fail to match because the failure doesn't happen on the line after the first message.


================
Comment at: compiler-rt/test/hwasan/TestCases/stack-history-length.c:20
+  // Bump the tag number so that OOB() doesn't end up with tag 0.
+  FUNC();
+
----------------
eugenis wrote:
> I don't understand this. How does a single additional call to FUNC help guarantee that property?
In the case where there are 2046 calls to `FUNC` we have:
- tag 1 for `FUNC0`
- tag 2..2047 (mod 256) for `FUNC1`
- tag 2048 (mod 256) for `OOB` (i.e. 0)
Adding the call to `FUNC` shifts all of the tags by 1 so that `OOB` gets tag 1.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D63360/new/

https://reviews.llvm.org/D63360