hwasan: Use system allocator to realloc and free untagged pointers in interceptor mode.

The Android dynamic loader has a non-standard feature that allows
libraries such as the hwasan runtime to interpose symbols even after
the symbol already has a value. The new value of the symbol is used to
relocate libraries loaded after the interposing library, but existing
libraries keep the old value. This behaviour is activated by the
DF_1_GLOBAL flag in DT_FLAGS_1, which is set by passing -z global to
the linker, which is what we already do to link the hwasan runtime.

What this means in practice is that if we have .so files that depend
on interceptor-mode hwasan without the main executable depending on
it, some of the libraries in the process will be using the hwasan
allocator and some will be using the system allocator, and these
allocators need to interact somehow. For example, if an instrumented
library calls a function such as strdup that allocates memory on
behalf of the caller, the instrumented library can reasonably expect
to be able to call free to deallocate the memory.

We can handle that relatively easily with hwasan by using tag 0 to
represent allocations from the system allocator. If hwasan's realloc
or free functions are passed a pointer with tag 0, the system allocator
is called.

One limitation is that this scheme doesn't work in reverse: if an
instrumented library allocates memory, it must free the memory itself
and cannot pass ownership to a system library. In a future change,
we may want to expose an API for calling the system allocator so
that instrumented libraries can safely transfer ownership of memory
to system libraries.

Differential Revision: https://reviews.llvm.org/D55986

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@350427 91177308-0d34-0410-b5e6-96231b3b80d8

6 files changed, 51 insertions, 13 deletions

diff --git a/lib/hwasan/hwasan.h b/lib/hwasan/hwasan.h
index 64b1f1a3d..ce9e904c5 100644
--- a/lib/hwasan/hwasan.h
+++ b/lib/hwasan/hwasan.h
@@ -77,7 +77,6 @@ void InitializeInterceptors();
 
 void HwasanAllocatorInit();
 void HwasanAllocatorThreadFinish();
-void HwasanDeallocate(StackTrace *stack, void *ptr);
 
 void *hwasan_malloc(uptr size, StackTrace *stack);
 void *hwasan_calloc(uptr nmemb, uptr size, StackTrace *stack);
@@ -88,6 +87,7 @@ void *hwasan_aligned_alloc(uptr alignment, uptr size, StackTrace *stack);
 void *hwasan_memalign(uptr alignment, uptr size, StackTrace *stack);
 int hwasan_posix_memalign(void **memptr, uptr alignment, uptr size,
                         StackTrace *stack);
+void hwasan_free(void *ptr, StackTrace *stack);
 
 void InstallTrapHandler();
 void InstallAtExitHandler();
diff --git a/lib/hwasan/hwasan_allocator.cc b/lib/hwasan/hwasan_allocator.cc
index 8fd2349d9..8487ed7e1 100644
--- a/lib/hwasan/hwasan_allocator.cc
+++ b/lib/hwasan/hwasan_allocator.cc
@@ -21,6 +21,11 @@
 #include "hwasan_thread.h"
 #include "hwasan_report.h"
 
+#if HWASAN_WITH_INTERCEPTORS
+DEFINE_REAL(void *, realloc, void *ptr, uptr size)
+DEFINE_REAL(void, free, void *ptr)
+#endif
+
 namespace __hwasan {
 
 static Allocator allocator;
@@ -199,7 +204,7 @@ static bool PointerAndMemoryTagsMatch(void *tagged_ptr) {
   return ptr_tag == mem_tag;
 }
 
-void HwasanDeallocate(StackTrace *stack, void *tagged_ptr) {
+static void HwasanDeallocate(StackTrace *stack, void *tagged_ptr) {
   CHECK(tagged_ptr);
   HWASAN_FREE_HOOK(tagged_ptr);
 
@@ -253,8 +258,8 @@ void HwasanDeallocate(StackTrace *stack, void *tagged_ptr) {
   }
 }
 
-void *HwasanReallocate(StackTrace *stack, void *tagged_ptr_old, uptr new_size,
-                     uptr alignment) {
+static void *HwasanReallocate(StackTrace *stack, void *tagged_ptr_old,
+                              uptr new_size, uptr alignment) {
   if (!PointerAndMemoryTagsMatch(tagged_ptr_old))
     ReportInvalidFree(stack, reinterpret_cast<uptr>(tagged_ptr_old));
 
@@ -271,7 +276,7 @@ void *HwasanReallocate(StackTrace *stack, void *tagged_ptr_old, uptr new_size,
   return tagged_ptr_new;
 }
 
-void *HwasanCalloc(StackTrace *stack, uptr nmemb, uptr size) {
+static void *HwasanCalloc(StackTrace *stack, uptr nmemb, uptr size) {
   if (UNLIKELY(CheckForCallocOverflow(size, nmemb))) {
     if (AllocatorMayReturnNull())
       return nullptr;
@@ -315,6 +320,14 @@ void *hwasan_calloc(uptr nmemb, uptr size, StackTrace *stack) {
 void *hwasan_realloc(void *ptr, uptr size, StackTrace *stack) {
   if (!ptr)
     return SetErrnoOnNull(HwasanAllocate(stack, size, sizeof(u64), false));
+
+#if HWASAN_WITH_INTERCEPTORS
+  // A tag of 0 means that this is a system allocator allocation, so we must use
+  // the system allocator to realloc it.
+  if (!flags()->disable_allocator_tagging && GetTagFromPointer((uptr)ptr) == 0)
+    return REAL(realloc)(ptr, size);
+#endif
+
   if (size == 0) {
     HwasanDeallocate(stack, ptr);
     return nullptr;
@@ -376,6 +389,17 @@ int hwasan_posix_memalign(void **memptr, uptr alignment, uptr size,
   return 0;
 }
 
+void hwasan_free(void *ptr, StackTrace *stack) {
+#if HWASAN_WITH_INTERCEPTORS
+  // A tag of 0 means that this is a system allocator allocation, so we must use
+  // the system allocator to free it.
+  if (!flags()->disable_allocator_tagging && GetTagFromPointer((uptr)ptr) == 0)
+    return REAL(free)(ptr);
+#endif
+
+  return HwasanDeallocate(stack, ptr);
+}
+
 }  // namespace __hwasan
 
 using namespace __hwasan;
@@ -385,6 +409,15 @@ void __hwasan_enable_allocator_tagging() {
 }
 
 void __hwasan_disable_allocator_tagging() {
+#if HWASAN_WITH_INTERCEPTORS
+  // Allocator tagging must be enabled for the system allocator fallback to work
+  // correctly. This means that we can't disable it at runtime if it was enabled
+  // at startup since that might result in our deallocations going to the system
+  // allocator. If tagging was disabled at startup we avoid this problem by
+  // disabling the fallback altogether.
+  CHECK(flags()->disable_allocator_tagging);
+#endif
+
   atomic_store_relaxed(&hwasan_allocator_tagging_enabled, 0);
 }
 
diff --git a/lib/hwasan/hwasan_allocator.h b/lib/hwasan/hwasan_allocator.h
index 785a80625..6ab722fa6 100644
--- a/lib/hwasan/hwasan_allocator.h
+++ b/lib/hwasan/hwasan_allocator.h
@@ -14,6 +14,7 @@
 #ifndef HWASAN_ALLOCATOR_H
 #define HWASAN_ALLOCATOR_H
 
+#include "interception/interception.h"
 #include "sanitizer_common/sanitizer_allocator.h"
 #include "sanitizer_common/sanitizer_allocator_checks.h"
 #include "sanitizer_common/sanitizer_allocator_interface.h"
@@ -26,6 +27,11 @@
 #error Unsupported platform
 #endif
 
+#if HWASAN_WITH_INTERCEPTORS
+DECLARE_REAL(void *, realloc, void *ptr, uptr size)
+DECLARE_REAL(void, free, void *ptr)
+#endif
+
 namespace __hwasan {
 
 struct Metadata {
diff --git a/lib/hwasan/hwasan_interceptors.cc b/lib/hwasan/hwasan_interceptors.cc
index d20bdd95a..533426c2e 100644
--- a/lib/hwasan/hwasan_interceptors.cc
+++ b/lib/hwasan/hwasan_interceptors.cc
@@ -17,6 +17,7 @@
 
 #include "interception/interception.h"
 #include "hwasan.h"
+#include "hwasan_allocator.h"
 #include "hwasan_mapping.h"
 #include "hwasan_thread.h"
 #include "hwasan_poisoning.h"
@@ -44,11 +45,6 @@ using __sanitizer::atomic_load;
 using __sanitizer::atomic_store;
 using __sanitizer::atomic_uintptr_t;
 
-DECLARE_REAL(SIZE_T, strlen, const char *s)
-DECLARE_REAL(SIZE_T, strnlen, const char *s, SIZE_T maxlen)
-DECLARE_REAL(void *, memcpy, void *dest, const void *src, uptr n)
-DECLARE_REAL(void *, memset, void *dest, int c, uptr n)
-
 bool IsInInterceptorScope() {
   Thread *t = GetCurrentThread();
   return t && t->InInterceptorScope();
@@ -130,13 +126,13 @@ void * __sanitizer_pvalloc(uptr size) {
 void __sanitizer_free(void *ptr) {
   GET_MALLOC_STACK_TRACE;
   if (!ptr || UNLIKELY(IsInDlsymAllocPool(ptr))) return;
-  HwasanDeallocate(&stack, ptr);
+  hwasan_free(ptr, &stack);
 }
 
 void __sanitizer_cfree(void *ptr) {
   GET_MALLOC_STACK_TRACE;
   if (!ptr || UNLIKELY(IsInDlsymAllocPool(ptr))) return;
-  HwasanDeallocate(&stack, ptr);
+  hwasan_free(ptr, &stack);
 }
 
 uptr __sanitizer_malloc_usable_size(const void *ptr) {
@@ -290,6 +286,8 @@ void InitializeInterceptors() {
 
 #if HWASAN_WITH_INTERCEPTORS
   INTERCEPT_FUNCTION(pthread_create);
+  INTERCEPT_FUNCTION(realloc);
+  INTERCEPT_FUNCTION(free);
 #endif
 
   inited = 1;
diff --git a/lib/hwasan/hwasan_linux.cc b/lib/hwasan/hwasan_linux.cc
index af9378c31..2238d3848 100644
--- a/lib/hwasan/hwasan_linux.cc
+++ b/lib/hwasan/hwasan_linux.cc
@@ -40,6 +40,7 @@
 #include "sanitizer_common/sanitizer_procmaps.h"
 
 #if HWASAN_WITH_INTERCEPTORS && !SANITIZER_ANDROID
+SANITIZER_INTERFACE_ATTRIBUTE
 THREADLOCAL uptr __hwasan_tls;
 #endif
 
diff --git a/lib/hwasan/hwasan_new_delete.cc b/lib/hwasan/hwasan_new_delete.cc
index 63ca74edd..f2e8faf5d 100644
--- a/lib/hwasan/hwasan_new_delete.cc
+++ b/lib/hwasan/hwasan_new_delete.cc
@@ -51,7 +51,7 @@ void *operator new[](size_t size, std::nothrow_t const&) {
 
 #define OPERATOR_DELETE_BODY \
   GET_MALLOC_STACK_TRACE; \
-  if (ptr) HwasanDeallocate(&stack, ptr)
+  if (ptr) hwasan_free(ptr, &stack)
 
 INTERCEPTOR_ATTRIBUTE
 void operator delete(void *ptr) NOEXCEPT { OPERATOR_DELETE_BODY; }