[asan] For iOS/AArch64, if the dynamic shadow doesn't fit, restrict the VM space

On iOS/AArch64, the address space is very limited and has a dynamic maximum address based on the configuration of the device. We're already using a dynamic shadow, and we find a large-enough "gap" in the VM where we place the shadow memory. In some cases and some device configuration, we might not be able to find a large-enough gap: E.g. if the main executable is linked against a large number of libraries that are not part of the system, these libraries can fragment the address space, and this happens before ASan starts initializing.

This patch has a solution, where we have a "backup plan" when we cannot find a large-enough gap: We will restrict the address space (via MmapFixedNoAccess) to a limit, for which the shadow limit will fit.

Differential Revision: https://reviews.llvm.org/D35098



git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@307865 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 30 insertions, 0 deletions

diff --git a/lib/sanitizer_common/sanitizer_mac_libcdep.cc b/lib/sanitizer_common/sanitizer_mac_libcdep.cc
new file mode 100644
index 000000000..c95daa937
--- /dev/null
+++ b/lib/sanitizer_common/sanitizer_mac_libcdep.cc
@@ -0,0 +1,30 @@
+//===-- sanitizer_mac_libcdep.cc ------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file is shared between various sanitizers' runtime libraries and
+// implements OSX-specific functions.
+//===----------------------------------------------------------------------===//
+
+#include "sanitizer_platform.h"
+#if SANITIZER_MAC
+#include "sanitizer_mac.h"
+
+#include <sys/mman.h>
+
+namespace __sanitizer {
+
+void RestrictMemoryToMaxAddress(uptr max_address) {
+  uptr size_to_mmap = GetMaxVirtualAddress() + 1 - max_address;
+  void *res = MmapFixedNoAccess(max_address, size_to_mmap, "high gap");
+  CHECK(res != MAP_FAILED);
+}
+
+}  // namespace __sanitizer
+
+#endif  // SANITIZER_MAC