[compiler-rt] bf0f874 - [scudo] Avoid splitting aligned allocations on Trusty (#69281)

[via llvm-commits]

Author: Andrei Homescu
Date: 2024-02-29T15:05:47-08:00
New Revision: bf0f874e4883a98ab69cff3da323713a5fe80dfd

URL: https://github.com/llvm/llvm-project/commit/bf0f874e4883a98ab69cff3da323713a5fe80dfd
DIFF: https://github.com/llvm/llvm-project/commit/bf0f874e4883a98ab69cff3da323713a5fe80dfd.diff

LOG: [scudo] Avoid splitting aligned allocations on Trusty (#69281)

Don't use multiple tagged pages at the beginning of an allocation, since
it prevents using such allocations for memrefs, and mappings aren't
reused anyway since Trusty uses MapAllocatorNoCache.
Upstreamed from https://r.android.com/2537251.

Co-authored-by: Marco Nelissen <marcone at google.com>

Added: 
    

Modified: 
    compiler-rt/lib/scudo/standalone/secondary.h

Removed: 
    


################################################################################
diff  --git a/compiler-rt/lib/scudo/standalone/secondary.h b/compiler-rt/lib/scudo/standalone/secondary.h
index f52a4188bcf3a6..732fd307ed2f43 100644
--- a/compiler-rt/lib/scudo/standalone/secondary.h
+++ b/compiler-rt/lib/scudo/standalone/secondary.h
@@ -122,7 +122,29 @@ bool mapSecondary(const Options &Options, uptr CommitBase, uptr CommitSize,
   Flags |= MAP_RESIZABLE;
   Flags |= MAP_ALLOWNOMEM;
 
-  const uptr MaxUnusedCacheBytes = MaxUnusedCachePages * getPageSizeCached();
+  const uptr PageSize = getPageSizeCached();
+  if (SCUDO_TRUSTY) {
+    /*
+     * On Trusty we need AllocPos to be usable for shared memory, which cannot
+     * cross multiple mappings. This means we need to split around AllocPos
+     * and not over it. We can only do this if the address is page-aligned.
+     */
+    const uptr TaggedSize = AllocPos - CommitBase;
+    if (useMemoryTagging<Config>(Options) && isAligned(TaggedSize, PageSize)) {
+      DCHECK_GT(TaggedSize, 0);
+      return MemMap.remap(CommitBase, TaggedSize, "scudo:secondary",
+                          MAP_MEMTAG | Flags) &&
+             MemMap.remap(AllocPos, CommitSize - TaggedSize, "scudo:secondary",
+                          Flags);
+    } else {
+      const uptr RemapFlags =
+          (useMemoryTagging<Config>(Options) ? MAP_MEMTAG : 0) | Flags;
+      return MemMap.remap(CommitBase, CommitSize, "scudo:secondary",
+                          RemapFlags);
+    }
+  }
+
+  const uptr MaxUnusedCacheBytes = MaxUnusedCachePages * PageSize;
   if (useMemoryTagging<Config>(Options) && CommitSize > MaxUnusedCacheBytes) {
     const uptr UntaggedPos = Max(AllocPos, CommitBase + MaxUnusedCacheBytes);
     return MemMap.remap(CommitBase, UntaggedPos - CommitBase, "scudo:secondary",