commit e254678b0705704d5bbba659dfecb534f240c819
author Vitaly Buka <vitalybuka@google.com> Fri May 28 02:08:44 2021 -0700
committer Copybara-Service <copybara-worker@google.com> Wed Jun 16 18:24:39 2021 -0700
tree b7971a8c3098bc4e60f66b64020a0f226beb1694
parent a64a5d112e2b46526d5e9d6300fdeb3e4c004c0e

[scudo] Always exclude Tag 0

prepareTaggedChunk uses Tag 0 for header.

Android already PR_MTE_TAG_MASK to 0xfffe,
but with the patch we will not need to deppend
on the system configuration.

Reviewed By: pcc

Differential Revision: https://reviews.llvm.org/D103134

GitOrigin-RevId: ba04c7c128b1214edf8888b129f9e841852a629b

memtag.h

diff --git a/memtag.h b/memtag.h
index fec258b..26502e2 100644
--- a/memtag.h
+++ b/memtag.h
@@ -158,6 +158,7 @@
 };
 
 inline uptr selectRandomTag(uptr Ptr, uptr ExcludeMask) {
+  ExcludeMask |= 1; // Always exclude Tag 0.
   uptr TaggedPtr;
   __asm__ __volatile__(
       R"(