[asan] Intercept and wrap XPC callback blocks

[kubamracek]

Summary

On recent OS X systems, blocks used as callbacks for XPC events (set up e.g. via xpc_connection_set_event_handler) are not later executed via the public libdispatch API (dispatch_async, etc). Because we don't intercept the path where the block is executed, we can fail to register the newly created dispatch thread. To fix that, let's intercept libxpc's APIs that take a block as a callback handler, and let's wrap these blocks in the same way as we do for libdispatch API.

[kubamracek]

ping

[glider]

How does this test check that the underlying thread(s) has been correctly registered?
Should we make the callback crash to make sure the report is correct?

lib/asan/asan_mac.cc

47

While at it, can you please fix the inclusion order?

test/asan/TestCases/Darwin/xpc_interceptors.mm

29

Why pass trace[0] to fprintf here?

[kubamracek]

In D12490#240066, @glider wrote:

How does this test check that the underlying thread(s) has been correctly registered?
Should we make the callback crash to make sure the report is correct?

__asan_get_alloc_stack will internally try to retrieve the thread from ThreadRegistry, which will currently (without the patch) crash.

[glider]

Got it. Can you please add a comment about this?

[kubamracek]

In D12490#240083, @glider wrote:

Got it. Can you please add a comment about this?

I'll change the test to perform a buffer overflow or something, that'll be better.

[kubamracek]

Updating patch to perform a buffer overflow in the XPC callback thread. Added comment explaining the bug. Fixed inclusion order.

[glider]

LGTM if xpc.h available on all OSX versions for which ASan is supported.

lib/asan/asan_mac.cc

46–47

Is this header available on all OSX versions we're targeting?

[kubamracek]

Yes, the APIs and the header is available on 10.7+.

[kubamracek]

Reverted in r246967. The header's not available in the simulator SDK.

lib/asan/asan_mac.cc

 #include <sys/mman.h>
 #include <sys/resource.h>
 #include <sys/sysctl.h>
 #include <sys/ucontext.h>
 #include <fcntl.h>
 #include <pthread.h>
 #include <stdlib.h>  // for free()
 #include <unistd.h>
 #include <libkern/OSAtomic.h>
+#include <xpc/xpc.h>
 
 namespace __asan {
 
 void InitializePlatformInterceptors() {}
 
 bool PlatformHasDifferentMemcpyAndMemmove() {
   // On OS X 10.7 memcpy() and memmove() are both resolved
   // into memmove$VARIANT$sse42.

 //   dispatch_source_set_event_handler_f()
 //   dispatch_source_set_event_handler()
 //
 // The reference manual for Grand Central Dispatch is available at
 //   http://developer.apple.com/library/mac/#documentation/Performance/Reference/GCD_libdispatch_Ref/Reference/reference.html
 // The implementation details are at
 //   http://libdispatch.macosforge.org/trac/browser/trunk/src/queue.c
 
-typedef void* dispatch_group_t;
-typedef void* dispatch_queue_t;
-typedef void* dispatch_source_t;
-typedef u64 dispatch_time_t;
-typedef void (*dispatch_function_t)(void *block);
 typedef void* (*worker_t)(void *block);
 
 // A wrapper for the ObjC blocks used to support libdispatch.
 typedef struct {
   void *block;
   dispatch_function_t func;
   u32 parent_tid;
 } asan_block_context_t;
#define GET_ASAN_BLOCK(work) \
   void (^asan_block)(void);  \
   int parent_tid = GetCurrentTidOrInvalid(); \
   asan_block = ^(void) { \
     GET_STACK_TRACE_THREAD; \
     asan_register_worker_thread(parent_tid, &stack); \
     work(); \
   }
 
+#define GET_ASAN_BLOCK_XPC(work) \
+  void (^asan_block)(xpc_object_t object);  \
+  int parent_tid = GetCurrentTidOrInvalid(); \
+  asan_block = ^(xpc_object_t object) { \
+    GET_STACK_TRACE_THREAD; \
+    asan_register_worker_thread(parent_tid, &stack); \
+    work(object); \
+  }
+
 INTERCEPTOR(void, dispatch_async,
             dispatch_queue_t dq, void(^work)(void)) {
   ENABLE_FRAME_POINTER;
   GET_ASAN_BLOCK(work);
   REAL(dispatch_async)(dq, asan_block);
 }
 
 INTERCEPTOR(void, dispatch_group_async,

 }
 
 INTERCEPTOR(void, dispatch_source_set_event_handler,
             dispatch_source_t ds, void(^work)(void)) {
   ENABLE_FRAME_POINTER;
   GET_ASAN_BLOCK(work);
   REAL(dispatch_source_set_event_handler)(ds, asan_block);
 }
+
+INTERCEPTOR(void, xpc_connection_send_message_with_reply,
+            xpc_connection_t connection, xpc_object_t message,
+            dispatch_queue_t replyq, xpc_handler_t handler) {
+  ENABLE_FRAME_POINTER;
+  GET_ASAN_BLOCK_XPC(handler);
+  REAL(xpc_connection_send_message_with_reply)(connection, message, replyq, asan_block);
+}
+
+INTERCEPTOR(void, xpc_connection_set_event_handler, xpc_connection_t connection,
+            xpc_handler_t handler) {
+  ENABLE_FRAME_POINTER;
+  GET_ASAN_BLOCK_XPC(handler);
+  REAL(xpc_connection_set_event_handler)(connection, asan_block);
+}
+
+INTERCEPTOR(void, xpc_set_event_stream_handler, const char *stream, dispatch_queue_t targetq,
+  xpc_handler_t handler) {
+  ENABLE_FRAME_POINTER;
+  GET_ASAN_BLOCK_XPC(handler);
+  REAL(xpc_set_event_stream_handler)(stream, targetq, asan_block);
+}
+
+INTERCEPTOR(void, xpc_connection_send_barrier, xpc_connection_t connection, 
+  dispatch_block_t barrier) {
+  ENABLE_FRAME_POINTER;
+  GET_ASAN_BLOCK(barrier);
+  REAL(xpc_connection_send_barrier)(connection, asan_block);
+}
+
 #endif
 
 #endif  // SANITIZER_MAC

test/asan/TestCases/Darwin/xpc_interceptors.mm

+// Check that blocks executed on the XPC callback queue are handled correctly by
+// ASan.
+
+// RUN: %clangxx_asan -O0 %s -o %t -framework Foundation && %run %t 2>&1 | FileCheck %s
+
+#import <Foundation/Foundation.h>
+#include <sanitizer/asan_interface.h>
+#include <xpc/xpc.h>
+
+int main() {
+  //!Set up a 5-second timeout.
+  dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 5 * NSEC_PER_SEC),
+                 dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0),
+                 ^{
+                   exit(1);
+                 });
+
+  xpc_connection_t _connection = xpc_connection_create_mach_service(
+      "com.example.non.existing.xpc", NULL, 0);
+
+  xpc_connection_set_event_handler(_connection, ^(xpc_object_t event) {
+    char *mem = (char *)malloc(10);
+    NSLog(@"mem = %p", mem);
+
+    void *trace[100];
+    size_t num_frames = 100;
+    int thread_id;
+    num_frames = __asan_get_alloc_stack(mem, trace, num_frames, &thread_id);
+    fprintf(stderr, "Okay.\n", trace[0]);
+    exit(0);
+  });
+
+  xpc_connection_resume(_connection);
+  dispatch_main();
+  return 0;
+}
+
+// CHECK: Okay.