[llvm-branch-commits] [compiler-rt] 07c19c3 - [compiler-rt] [Darwin] Move macOS ASAN reservation above 512G (#191039)

[Cullen Rhodes via llvm-branch-commits]

Author: Andrew Haberlandt
Date: 2026-04-17T10:00:08Z
New Revision: 07c19c30338729db01d363757e511c4306954764

URL: https://github.com/llvm/llvm-project/commit/07c19c30338729db01d363757e511c4306954764
DIFF: https://github.com/llvm/llvm-project/commit/07c19c30338729db01d363757e511c4306954764.diff

LOG: [compiler-rt] [Darwin] Move macOS ASAN reservation above 512G (#191039)

On macOS, the first 512G may contain platform-specific reservations. To
ensure compatibility with these reservations, this changes ASAN to
always map shadow memory above 512G on macOS.

rdar://174252720
(cherry picked from commit 857a98e50e279c0c1cf3658337dadb347f7ff5c4)

Added: 
    

Modified: 
    compiler-rt/lib/sanitizer_common/sanitizer_mac.cpp
    compiler-rt/lib/sanitizer_common/sanitizer_mac.h

Removed: 
    


################################################################################
diff  --git a/compiler-rt/lib/sanitizer_common/sanitizer_mac.cpp b/compiler-rt/lib/sanitizer_common/sanitizer_mac.cpp
index 3f8de8dd064a5..940175791f376 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_mac.cpp
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_mac.cpp
@@ -1288,6 +1288,25 @@ uptr MapDynamicShadow(uptr shadow_size_bytes, uptr shadow_scale,
   return shadow_start;
 }
 
+// Returns a list of ranges which must be covered by shadow memory,
+// and cannot overlap with any fixed mappings made by a sanitizer.
+// This can ensure that the sanitizer runtime does not map over
+// platform-reserved regions.
+void GetAppReservedRanges(InternalMmapVector<ReservedRange>& ranges) {
+  ranges.clear();
+
+#  if SANITIZER_OSX
+  // On macOS, the first 512GB are platform-reserved (some of which
+  // may also be available to applications).
+  ranges.push_back({0x1000UL, 0x8000000000UL});
+#  endif
+
+  VReport(2, "App ranges:\n");
+  for (auto& [range_start, range_end] : ranges) {
+    VReport(2, "  [%p, %p]\n", range_start, range_end);
+  }
+}
+
 uptr MapDynamicShadowAndAliases(uptr shadow_size, uptr alias_size,
                                 uptr num_aliases, uptr ring_buffer_size) {
   CHECK(false && "HWASan aliasing is unimplemented on Mac");
@@ -1300,6 +1319,16 @@ uptr FindAvailableMemoryRange(uptr size, uptr alignment, uptr left_padding,
   const mach_vm_address_t max_vm_address = GetMaxVirtualAddress() + 1;
   mach_vm_address_t address = GAP_SEARCH_START_ADDRESS;
   mach_vm_address_t free_begin = GAP_SEARCH_START_ADDRESS;
+
+  // Restrict the search to be after any reserved ranges
+  InternalMmapVector<ReservedRange> app_ranges;
+  GetAppReservedRanges(app_ranges);
+
+  for (auto& [range_start, range_end] : app_ranges) {
+    address = Max(address, (mach_vm_address_t)range_end);
+    free_begin = Max(free_begin, (mach_vm_address_t)range_end);
+  }
+
   kern_return_t kr = KERN_SUCCESS;
   if (largest_gap_found) *largest_gap_found = 0;
   if (max_occupied_addr) *max_occupied_addr = 0;

diff  --git a/compiler-rt/lib/sanitizer_common/sanitizer_mac.h b/compiler-rt/lib/sanitizer_common/sanitizer_mac.h
index b0e4ac7f40745..7f9a2b77e7d50 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_mac.h
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_mac.h
@@ -58,8 +58,13 @@ struct DarwinKernelVersion : VersionBase<DarwinKernelVersion> {
   DarwinKernelVersion(u16 major, u16 minor) : VersionBase(major, minor) {}
 };
 
+struct ReservedRange {
+  uptr beg, end;
+};
+
 MacosVersion GetMacosAlignedVersion();
 DarwinKernelVersion GetDarwinKernelVersion();
+void GetAppReservedRanges(InternalMmapVector<ReservedRange>& ranges);
 
 char **GetEnviron();