[compiler-rt] c6ad3f2 - [asan][fuchsia] Implement PlatformUnpoisonStacks

[Marco Vanotti via llvm-commits]

Author: Marco Vanotti
Date: 2021-07-28T18:02:19-07:00
New Revision: c6ad3f2157ce374dbd2fd3e50699fc0303553714

URL: https://github.com/llvm/llvm-project/commit/c6ad3f2157ce374dbd2fd3e50699fc0303553714
DIFF: https://github.com/llvm/llvm-project/commit/c6ad3f2157ce374dbd2fd3e50699fc0303553714.diff

LOG: [asan][fuchsia] Implement PlatformUnpoisonStacks

This CL modifies the PlatformUnpoisonStacks so that fuchsia can
implement its own logic for unpoisoning the stacks.

For the general case, the behavior is the same as with regular asan: it
will unpoison everything from the current stack pointer until the base
of the stack (stack top).

In some situations, the current stack might not be the same as the
default stack. In those cases, the code will now unpoison the entire
default stack, and will also unpoison the current page of the stack.

Reviewed By: mcgrathr

Differential Revision: https://reviews.llvm.org/D106835

Added: 
    

Modified: 
    compiler-rt/lib/asan/asan_fuchsia.cpp

Removed: 
    


################################################################################
diff  --git a/compiler-rt/lib/asan/asan_fuchsia.cpp b/compiler-rt/lib/asan/asan_fuchsia.cpp
index b0c7255144ac..b419019d137d 100644
--- a/compiler-rt/lib/asan/asan_fuchsia.cpp
+++ b/compiler-rt/lib/asan/asan_fuchsia.cpp
@@ -31,7 +31,8 @@ namespace __asan {
 // AsanInitInternal->InitializeHighMemEnd (asan_rtl.cpp).
 // Just do some additional sanity checks here.
 void InitializeShadowMemory() {
-  if (Verbosity()) PrintAddressSpaceLayout();
+  if (Verbosity())
+    PrintAddressSpaceLayout();
 
   // Make sure SHADOW_OFFSET doesn't use __asan_shadow_memory_dynamic_address.
   __asan_shadow_memory_dynamic_address = kDefaultShadowSentinel;
@@ -62,7 +63,34 @@ void AsanOnDeadlySignal(int signo, void *siginfo, void *context) {
   UNIMPLEMENTED();
 }
 
-bool PlatformUnpoisonStacks() { return false; }
+bool PlatformUnpoisonStacks() {
+  // The current sp might not point to the default stack. This
+  // could be because we are in a crash stack from fuzzing for example.
+  // Unpoison the default stack and the current stack page.
+  AsanThread *curr_thread = GetCurrentThread();
+  CHECK(curr_thread != nullptr);
+  uptr top = curr_thread->stack_top();
+  uptr bottom = curr_thread->stack_bottom();
+  // The default stack grows from top to bottom. (bottom < top).
+
+  uptr local_stack = reinterpret_cast<uptr>(__builtin_frame_address(0));
+  if (local_stack >= bottom && local_stack <= top) {
+    // The current stack is the default stack.
+    // We only need to unpoison from where we are using until the end.
+    bottom = RoundDownTo(local_stack, GetPageSize());
+    UnpoisonStack(bottom, top, "default");
+  } else {
+    // The current stack is not the default stack.
+    // Unpoison the entire default stack and the current stack page.
+    UnpoisonStack(bottom, top, "default");
+    bottom = RoundDownTo(local_stack, GetPageSize());
+    top = bottom + GetPageSize();
+    UnpoisonStack(bottom, top, "unknown");
+    return true;
+  }
+
+  return false;
+}
 
 // We can use a plain thread_local variable for TSD.
 static thread_local void *per_thread;
@@ -148,7 +176,8 @@ static void *BeforeThreadCreateHook(uptr user_id, bool detached,
                                     uptr stack_size) {
   EnsureMainThreadIDIsCorrect();
   // Strict init-order checking is thread-hostile.
-  if (flags()->strict_init_order) StopInitOrderChecking();
+  if (flags()->strict_init_order)
+    StopInitOrderChecking();
 
   GET_STACK_TRACE_THREAD;
   u32 parent_tid = GetCurrentTidOrInvalid();