Give V8 a chance to handle faults in stack dump crash handler

V8 has the ability to use guard regions and signal handlers to do WebAssembly
bounds checks on x86_64 Linux. This requires any in-process signal handlers to
let V8 try to handle the signal first. This CL adds support for this to the
stack dump signal handler.

Bug: chromium:722585, v8:5277
Change-Id: Iccb72b66118c743f78b3ddbaf7887728b213ddb2
Reviewed-on: https://chromium-review.googlesource.com/541956Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Reviewed-by: Mark Mentovai <mark@chromium.org>
Commit-Queue: Eric Holk <eholk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487153}

base/debug/stack_trace.h

@@ -38,6 +38,12 @@ namespace debug {
 // done in official builds because it has security implications).
 BASE_EXPORT bool EnableInProcessStackDumping();
 
+#if defined(OS_POSIX)
+BASE_EXPORT void SetStackDumpFirstChanceCallback(bool (*handler)(int,
+                                                                 void*,
+                                                                 void*));
+#endif
+
 // Returns end of the stack, or 0 if we couldn't get it.
 #if BUILDFLAG(CAN_UNWIND_WITH_FRAME_POINTERS)
 BASE_EXPORT uintptr_t GetStackEnd();

base/debug/stack_trace_posix.cc

@@ -59,6 +59,8 @@ namespace {
 
 volatile sig_atomic_t in_signal_handler = 0;
 
+bool (*try_handle_signal)(int, void*, void*) = nullptr;
+
 #if !defined(USE_SYMBOLIZE)
 // The prefix used for mangled symbols, per the Itanium C++ ABI:
 // http://www.codesourcery.com/cxx-abi/abi.html#mangling
@@ -216,6 +218,27 @@ void StackDumpSignalHandler(int signal, siginfo_t* info, void* void_context) {
   // NOTE: This code MUST be async-signal safe.
   // NO malloc or stdio is allowed here.
 
+  // Give a registered callback a chance to recover from this signal
+  //
+  // V8 uses guard regions to guarantee memory safety in WebAssembly. This means
+  // some signals might be expected if they originate from Wasm code while
+  // accessing the guard region. We give V8 the chance to handle and recover
+  // from these signals first.
+  if (try_handle_signal != nullptr &&
+      try_handle_signal(signal, info, void_context)) {
+    // The first chance handler took care of this. The SA_RESETHAND flag
+    // replaced this signal handler upon entry, but we want to stay
+    // installed. Thus, we reinstall ourselves before returning.
+    struct sigaction action;
+    memset(&action, 0, sizeof(action));
+    action.sa_flags = SA_RESETHAND | SA_SIGINFO;
+    action.sa_sigaction = &StackDumpSignalHandler;
+    sigemptyset(&action.sa_mask);
+
+    sigaction(signal, &action, NULL);
+    return;
+  }
+
   // Record the fact that we are in the signal handler now, so that the rest
   // of StackTrace can behave in an async-signal-safe manner.
   in_signal_handler = 1;
@@ -717,6 +740,11 @@ bool EnableInProcessStackDumping() {
   return success;
 }
 
+void SetStackDumpFirstChanceCallback(bool (*handler)(int, void*, void*)) {
+  DCHECK(try_handle_signal == nullptr || handler == nullptr);
+  try_handle_signal = handler;
+}
+
 StackTrace::StackTrace(size_t count) {
 // NOTE: This code MUST be async-signal safe (it's used by in-process
 // stack dumping signal handler). NO malloc or stdio is allowed here.

content/renderer/render_process_impl.cc

@@ -21,6 +21,7 @@
 #include "base/command_line.h"
 #include "base/compiler_specific.h"
 #include "base/debug/crash_logging.h"
+#include "base/debug/stack_trace.h"
 #include "base/feature_list.h"
 #include "base/memory/ptr_util.h"
 #include "base/sys_info.h"
@@ -144,10 +145,16 @@ RenderProcessImpl::RenderProcessImpl(
   SetV8FlagIfFeature(features::kAsmJsToWebAssembly, "--validate-asm");
   SetV8FlagIfNotFeature(features::kWebAssembly,
                         "--wasm-disable-structured-cloning");
-  SetV8FlagIfFeature(features::kWebAssemblyTrapHandler, "--wasm-trap-handler");
   SetV8FlagIfFeature(features::kSharedArrayBuffer,
                      "--harmony-sharedarraybuffer");
 
+  SetV8FlagIfFeature(features::kWebAssemblyTrapHandler, "--wasm-trap-handler");
+#if defined(OS_LINUX) && defined(ARCH_CPU_X86_64) && !defined(OS_ANDROID)
+  if (base::FeatureList::IsEnabled(features::kWebAssemblyTrapHandler)) {
+    base::debug::SetStackDumpFirstChanceCallback(v8::V8::TryHandleSignal);
+  }
+#endif
+
   const base::CommandLine& command_line =
       *base::CommandLine::ForCurrentProcess();