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

@@ -217,17 +217,33 @@ void FakeStack::ForEachFakeFrame(RangeIteratorCallback callback, void* arg) {
 static THREADLOCAL FakeStack* fake_stack_tls;
 
 static FakeStack* GetTLSFakeStack() { return fake_stack_tls; }
-static void SetTLSFakeStack(FakeStack* fs) { fake_stack_tls = fs; }
+static void SetTLSFakeStack(FakeStack* fs) {
+  fake_stack_tls = fs;
+}
 void ResetTLSFakeStack() { fake_stack_tls = nullptr; }
 #else
 static FakeStack* GetTLSFakeStack() { return nullptr; }
-static void SetTLSFakeStack(FakeStack*) {}
+static void SetTLSFakeStack(FakeStack* fs) {}
 void ResetTLSFakeStack() {}
 #endif  // (SANITIZER_LINUX && !SANITIZER_ANDROID) || SANITIZER_FUCHSIA
 
+static void DisableFakeStack() {
+  AsanThread* t = GetCurrentThread();
+  if (t) {
+    t->SetFakeStackEnabled(false);
+  }
+}
+
+static void EnableFakeStack() {
+  AsanThread* t = GetCurrentThread();
+  if (t) {
+    t->SetFakeStackEnabled(true);
+  }
+}
+
 static FakeStack* GetFakeStack() {
   AsanThread* t = GetCurrentThread();
-  if (!t)
+  if (!t || !t->IsFakeStackEnabled())
     return nullptr;
   return t->get_or_create_fake_stack();
 }
@@ -362,4 +378,9 @@ void __asan_allocas_unpoison(uptr top, uptr bottom) {
   REAL(memset)(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_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

@@ -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

@@ -144,6 +144,12 @@ class AsanThread {
     GetStartData(&data, sizeof(data));
   }
 
+  bool IsFakeStackEnabled() const { return fake_stack_enabled_; }
+  void SetFakeStackEnabled(bool enabled) {
+    fake_stack_enabled_ = enabled;
+    ResetTLSFakeStack();
+  }
+
  private:
   // NOTE: There is no AsanThread constructor. It is allocated
   // via mmap() and *must* be valid in zero-initialized state.
@@ -179,6 +185,7 @@ 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;
+}