Add API to temporalily disable usage of ASAN's fake stack

Intended use-case is for threads that use (or switch to) stack
with special properties e.g. backed by MADV_DONTDUMP memory.

Author: happyCoder92

compiler-rt/include/sanitizer/asan_interface.h

@@ -333,6 +333,13 @@ void SANITIZER_CDECL __asan_handle_no_return(void);
 /// trace. Returns 1 if successful, 0 if not.
 int SANITIZER_CDECL __asan_update_allocation_context(void *addr);
 
+/// Disables fake stack for the current thread.
+/// Temporarily disables use-after-return detection for current thread.
+void SANITIZER_CDECL __asan_disable_fake_stack(void);
+
+/// (Re)enables fake stack for the current thread.
+void SANITIZER_CDECL __asan_enable_fake_stack(void);
+
 #ifdef __cplusplus
 } // extern "C"
 #endif

compiler-rt/lib/asan/asan_fake_stack.cpp

@@ -217,26 +217,44 @@ static THREADLOCAL FakeStack *fake_stack_tls;
 FakeStack *GetTLSFakeStack() {
   return fake_stack_tls;
 }
-void SetTLSFakeStack(FakeStack *fs) {
+void SetTLSFakeStack(AsanThread* t, FakeStack* fs) {
+  if (fs && !t->IsFakeStackEnabled()) {
+    return;
+  }
   fake_stack_tls = fs;
 }
 #else
 FakeStack *GetTLSFakeStack() { return 0; }
-void SetTLSFakeStack(FakeStack *fs) { }
+void SetTLSFakeStack(AsanThread* t, FakeStack* fs) {}
 #endif  // (SANITIZER_LINUX && !SANITIZER_ANDROID) || SANITIZER_FUCHSIA
 
-static FakeStack *GetFakeStack() {
+static void DisableFakeStack() {
   AsanThread *t = GetCurrentThread();
-  if (!t) return nullptr;
+  if (t) {
+    t->SetFakeStackEnabled(false);
+  }
+}
+
+static void EnableFakeStack() {
+  AsanThread* t = GetCurrentThread();
+  if (t) {
+    t->SetFakeStackEnabled(true);
+  }
+}
+
+static FakeStack* GetFakeStack(bool for_allocation = true) {
+  AsanThread* t = GetCurrentThread();
+  if (!t || (for_allocation && !t->IsFakeStackEnabled()))
+    return nullptr;
   return t->get_or_create_fake_stack();
 }
 
-static FakeStack *GetFakeStackFast() {
+static FakeStack* GetFakeStackFast(bool for_allocation = true) {
   if (FakeStack *fs = GetTLSFakeStack())
     return fs;
   if (!__asan_option_detect_stack_use_after_return)
     return nullptr;
-  return GetFakeStack();
+  return GetFakeStack(for_allocation);
 }
 
 static FakeStack *GetFakeStackFastAlways() {
@@ -311,7 +329,9 @@ extern "C" {
 // -asan-use-after-return=never, after modal UAR flag lands
 // (https://github.com/google/sanitizers/issues/1394)
 SANITIZER_INTERFACE_ATTRIBUTE
-void *__asan_get_current_fake_stack() { return GetFakeStackFast(); }
+void* __asan_get_current_fake_stack() {
+  return GetFakeStackFast(/*for_allocation=*/false);
+}
 
 SANITIZER_INTERFACE_ATTRIBUTE
 void *__asan_addr_is_in_fake_stack(void *fake_stack, void *addr, void **beg,
@@ -349,4 +369,9 @@ void __asan_allocas_unpoison(uptr top, uptr bottom) {
   (reinterpret_cast<void *>(MemToShadow(top)), 0,
    (bottom - top) / ASAN_SHADOW_GRANULARITY);
 }
+
+SANITIZER_INTERFACE_ATTRIBUTE
+void __asan_disable_fake_stack() { return DisableFakeStack(); }
+SANITIZER_INTERFACE_ATTRIBUTE
+void __asan_enable_fake_stack() { return EnableFakeStack(); }
 } // extern "C"

compiler-rt/lib/asan/asan_fake_stack.h

@@ -18,6 +18,8 @@
 
 namespace __asan {
 
+class AsanThread;
+
 // Fake stack frame contains local variables of one function.
 struct FakeFrame {
   uptr magic;  // Modified by the instrumented code.
@@ -196,7 +198,7 @@ class FakeStack {
 };
 
 FakeStack *GetTLSFakeStack();
-void SetTLSFakeStack(FakeStack *fs);
+void SetTLSFakeStack(AsanThread* t, FakeStack* fs);
 
 }  // namespace __asan
 

compiler-rt/lib/asan/asan_interface.inc

@@ -15,6 +15,8 @@ INTERFACE_FUNCTION(__asan_alloca_poison)
 INTERFACE_FUNCTION(__asan_allocas_unpoison)
 INTERFACE_FUNCTION(__asan_before_dynamic_init)
 INTERFACE_FUNCTION(__asan_describe_address)
+INTERFACE_FUNCTION(__asan_disable_fake_stack)
+INTERFACE_FUNCTION(__asan_enable_fake_stack)
 INTERFACE_FUNCTION(__asan_exp_load1)
 INTERFACE_FUNCTION(__asan_exp_load2)
 INTERFACE_FUNCTION(__asan_exp_load4)

compiler-rt/lib/asan/asan_thread.cpp

@@ -163,7 +163,7 @@ void AsanThread::StartSwitchFiber(FakeStack **fake_stack_save, uptr bottom,
   if (fake_stack_save)
     *fake_stack_save = fake_stack_;
   fake_stack_ = nullptr;
-  SetTLSFakeStack(nullptr);
+  SetTLSFakeStack(this, nullptr);
   // if fake_stack_save is null, the fiber will die, delete the fakestack
   if (!fake_stack_save && current_fake_stack)
     current_fake_stack->Destroy(this->tid());
@@ -177,7 +177,7 @@ void AsanThread::FinishSwitchFiber(FakeStack *fake_stack_save, uptr *bottom_old,
   }
 
   if (fake_stack_save) {
-    SetTLSFakeStack(fake_stack_save);
+    SetTLSFakeStack(this, fake_stack_save);
     fake_stack_ = fake_stack_save;
   }
 
@@ -242,7 +242,7 @@ FakeStack *AsanThread::AsyncSignalSafeLazyInitFakeStack() {
         Max(stack_size_log, static_cast<uptr>(flags()->min_uar_stack_size_log));
     fake_stack_ = FakeStack::Create(stack_size_log);
     DCHECK_EQ(GetCurrentThread(), this);
-    SetTLSFakeStack(fake_stack_);
+    SetTLSFakeStack(this, fake_stack_);
     return fake_stack_;
   }
   return nullptr;
@@ -251,6 +251,7 @@ FakeStack *AsanThread::AsyncSignalSafeLazyInitFakeStack() {
 void AsanThread::Init(const InitOptions *options) {
   DCHECK_NE(tid(), kInvalidTid);
   next_stack_top_ = next_stack_bottom_ = 0;
+  fake_stack_enabled_ = true;
   atomic_store(&stack_switching_, false, memory_order_release);
   CHECK_EQ(this->stack_size(), 0U);
   SetThreadStackAndTls(options);

compiler-rt/lib/asan/asan_thread.h

@@ -104,7 +104,7 @@ class AsanThread {
     if (!fake_stack_) return;
     FakeStack *t = fake_stack_;
     fake_stack_ = nullptr;
-    SetTLSFakeStack(nullptr);
+    SetTLSFakeStack(this, nullptr);
     t->Destroy(tid);
   }
 
@@ -144,6 +144,14 @@ class AsanThread {
     GetStartData(&data, sizeof(data));
   }
 
+  bool IsFakeStackEnabled() const { return fake_stack_enabled_; }
+  void SetFakeStackEnabled(bool enabled) {
+    fake_stack_enabled_ = enabled;
+    if (!enabled) {
+      SetTLSFakeStack(this, nullptr);
+    }
+  }
+
  private:
   // NOTE: There is no AsanThread constructor. It is allocated
   // via mmap() and *must* be valid in zero-initialized state.
@@ -179,6 +187,7 @@ class AsanThread {
   DTLS *dtls_;
 
   FakeStack *fake_stack_;
+  bool fake_stack_enabled_;
   AsanThreadLocalMallocStorage malloc_storage_;
   AsanStats stats_;
   bool unwinding_;

compiler-rt/lib/asan_abi/asan_abi.cpp

@@ -73,6 +73,8 @@ void *__asan_abi_addr_is_in_fake_stack(void *fake_stack, void *addr, void **beg,
                                        void **end) {
   return NULL;
 }
+void __asan_abi_disable_fake_stack(void) {}
+void __asan_abi_enable_fake_stack(void) {}
 
 // Functions concerning poisoning and unpoisoning fake stack alloca
 void __asan_abi_alloca_poison(void *addr, size_t size) {}

compiler-rt/lib/asan_abi/asan_abi.h

@@ -76,6 +76,9 @@ void *__asan_abi_load_cxx_array_cookie(void **p);
 void *__asan_abi_get_current_fake_stack();
 void *__asan_abi_addr_is_in_fake_stack(void *fake_stack, void *addr, void **beg,
                                        void **end);
+void *__asan_abi_disable_fake_stack();
+void *__asan_abi_enable_fake_stack();
+
 // Functions concerning poisoning and unpoisoning fake stack alloca
 void __asan_abi_alloca_poison(void *addr, size_t size);
 void __asan_abi_allocas_unpoison(void *top, void *bottom);

compiler-rt/lib/asan_abi/asan_abi_shim.cpp

@@ -365,6 +365,8 @@ void *__asan_addr_is_in_fake_stack(void *fake_stack, void *addr, void **beg,
                                    void **end) {
   return __asan_abi_addr_is_in_fake_stack(fake_stack, addr, beg, end);
 }
+void __asan_disable_fake_stack(void) { return __asan_abi_disable_fake_stack(); }
+void __asan_enable_fake_stack(void) { return __asan_abi_enable_fake_stack(); }
 
 // Functions concerning poisoning and unpoisoning fake stack alloca
 void __asan_alloca_poison(uptr addr, uptr size) {

compiler-rt/test/asan/TestCases/disable_fake_stack.cpp

@@ -0,0 +1,28 @@
+// RUN: %clangxx_asan %s -o %t && %run %t
+
+#include "defines.h"
+
+#include <sanitizer/asan_interface.h>
+
+volatile char *saved;
+
+ATTRIBUTE_NOINLINE bool IsOnStack() {
+  volatile char temp = ' ';
+  void *fake_stack = __asan_get_current_fake_stack();
+  void *real = __asan_addr_is_in_fake_stack(
+      fake_stack, const_cast<char *>(&temp), nullptr, nullptr);
+  saved = &temp;
+  return real == nullptr;
+}
+
+int main(int argc, char *argv[]) {
+  __asan_disable_fake_stack();
+  if (!IsOnStack()) {
+    return 1;
+  }
+  __asan_enable_fake_stack();
+  if (IsOnStack()) {
+    return 2;
+  }
+  return 0;
+}