[wasm] Initial signal handler

src/trap-handler/trap-handler.cc

+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// PLEASE READ BEFORE CHANGING THIS FILE!
+//
+// This file implements the out of bounds signal handler for
+// WebAssembly. Signal handlers are notoriously difficult to get
+// right, and getting it wrong can lead to security
+// vulnerabilities. In order to minimize this risk, here are some
+// rules to follow.
+//
+// 1. Do not introduce any new external dependencies. This file needs
+//    to be self contained so it is easy to audit everything that a
+//    signal handler might do.
+//
+// 2. Any changes must be reviewed by someone from the crash reporting
+//    or security team.
+
+// This file contains general support code for trap handling, and is mostly
+// used by other parts of V8. For the code that runs in the signal handler
+// itself, see signal-handler.cc.
+
+#include <signal.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <atomic>
+
+#include "src/flags.h"
+#include "src/trap-handler/trap-handler-internal.h"
+#include "src/trap-handler/trap-handler.h"
+
+#define TRACE(...)
+
+namespace v8 {
+namespace internal {
+namespace trap_handler {
+
+THREAD_LOCAL bool g_thread_in_wasm_code = false;
+
+const size_t kInitialCodeObjectSize = 1024;
+const size_t kCodeObjectGrowthFactor = 2;
+size_t gNumCodeObjects = 0;
+CodeProtectionInfo** gCodeObjects = nullptr;
+
+std::atomic_flag MetadataLock::spinlock_ = ATOMIC_FLAG_INIT;
+
+constexpr size_t HandlerDataSize(size_t num_protected_instructions) {
+  return offsetof(CodeProtectionInfo, instructions) +
+         num_protected_instructions * sizeof(ProtectedInstructionData);
+}
+
+CodeProtectionInfo* CreateHandlerData(
+    void* base, size_t size, size_t num_protected_instructions,
+    ProtectedInstructionData* protected_instructions) {
+  const size_t alloc_size = HandlerDataSize(num_protected_instructions);
+  CodeProtectionInfo* data =
+      reinterpret_cast<CodeProtectionInfo*>(malloc(alloc_size));
+
+  if (data == nullptr) {
+    return nullptr;
+  }
+
+  data->base = base;
+  data->size = size;
+  data->num_protected_instructions = num_protected_instructions;
+
+  memcpy(data->instructions, protected_instructions,
+         num_protected_instructions * sizeof(ProtectedInstructionData));
+
+  return data;
+}
+
+void UpdateCodePointer(int index, void* base) {
+  TRACE("Updating code pointer at index %d\n", index);
+  MetadataLock lock;
+  if (static_cast<size_t>(index) >= gNumCodeObjects) {
+    TRACE("Out of bounds\n");
+    abort();
+  }
+  CodeProtectionInfo* data = gCodeObjects[index];
+  data->base = base;
+}
+
+int RegisterHandlerData(void* base, size_t size,
+                        size_t num_protected_instructions,
+                        ProtectedInstructionData* protected_instructions) {
+  // TODO(eholk): in debug builds, make sure this data isn't already registered.
+
+  CodeProtectionInfo* data = CreateHandlerData(
+      base, size, num_protected_instructions, protected_instructions);
+
+  if (data == nullptr) {
+    TRACE("Could not allocate handler data\n");
+    abort();
+  }
+
+  MetadataLock lock;
+
+  size_t i;
+  for (i = 0; i < gNumCodeObjects; ++i) {
+    if (gCodeObjects[i] == nullptr) {
+      break;
+    }
+  }
+
+  // We didn't find an opening in the available space, so grow.
+  if (i == gNumCodeObjects) {
+    size_t new_size = gNumCodeObjects > 0
+                          ? gNumCodeObjects * kCodeObjectGrowthFactor
+                          : kInitialCodeObjectSize;
+    gCodeObjects = static_cast<CodeProtectionInfo**>(
+        realloc(gCodeObjects, sizeof(*gCodeObjects) * new_size));
+
+    if (gCodeObjects == nullptr) {
+      abort();
+    }
+
+    memset(gCodeObjects + gNumCodeObjects, 0,
+           sizeof(*gCodeObjects) * (new_size - gNumCodeObjects));
+    gNumCodeObjects = new_size;
+  }
+
+  gCodeObjects[i] = data;
+  TRACE("Registered handler data %p at index %zu\n", data, i);
+  return static_cast<int>(i);
+}
+
+void ReleaseHandlerData(int index) {
+  // Remove the data from the global list if it's there.
+
+  MetadataLock lock;
+
+  CodeProtectionInfo* data = gCodeObjects[index];
+  gCodeObjects[index] = nullptr;
+
+  TRACE("Released handler data %p at index %d\n", data, index);
+
+  // TODO(eholk): on debug builds, ensure there are no more copies in
+  // the list.
+  free(data);
+}
+
+void SetThreadInWasm() {
+  TRACE("Transitioning to Wasm\n");
+  g_thread_in_wasm_code = true;
+}
+
+void ClearThreadInWasm() {
+  TRACE("Transitioning from Wasm\n");
+  g_thread_in_wasm_code = false;
+}
+
+bool IsThreadInWasm() { return g_thread_in_wasm_code; }
+
+bool EnableTrapHandler() {
+  return FLAG_wasm_trap_handler && kTrapHandlerSupported;
+}
+
+}  // namespace trap_handler
+}  // namespace internal
+}  // namespace v8