Added API to verify version match on snapshot blob

This patch added an IsValid method to StartupData which returns a
boolean upon verifying a given snapshot matches the v8 version.
Embedders can use this API now to check snapshots' versions.

This was originally done by Snapshot::CheckVersion, which now simply
runs Startup::IsValid.

Bug: v8:8104
Change-Id: If555bcc55de4a05adf61798cd58d9ea8c8a71302
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2178091
Commit-Queue: Yang Guo <yangguo@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Auto-Submit: Junha Park <jpark3@scu.edu>
Cr-Commit-Position: refs/heads/master@{#67951}

AUTHORS

@@ -118,6 +118,7 @@ Joel Stanley <joel@jms.id.au>
 Johan Bergström <johan@bergstroem.nu>
 Jonathan Liu <net147@gmail.com>
 Julien Brianceau <jbriance@cisco.com>
+Junha Park <jpark3@scu.edu>
 JunHo Seo <sejunho@gmail.com>
 Junming Huang <kiminghjm@gmail.com>
 Kang-Hao (Kenny) Lu <kennyluck@csail.mit.edu>

include/v8.h

@@ -9499,12 +9499,16 @@ class V8_EXPORT StartupData {
    * Only valid for StartupData returned by SnapshotCreator::CreateBlob().
    */
   bool CanBeRehashed() const;
+  /**
+   * Allows embedders to verify whether the data is valid for the current
+   * V8 instance.
+   */
+  bool IsValid() const;
 
   const char* data;
   int raw_size;
 };
 
-
 /**
  * EntropySource is used as a callback function when v8 needs a source
  * of entropy.

src/api/api.cc

@@ -823,6 +823,8 @@ bool StartupData::CanBeRehashed() const {
   return i::Snapshot::ExtractRehashability(this);
 }
 
+bool StartupData::IsValid() const { return i::Snapshot::VersionIsValid(this); }
+
 void V8::SetDcheckErrorHandler(DcheckErrorCallback that) {
   v8::base::SetDcheckFunction(that);
 }

src/snapshot/snapshot.cc

@@ -128,6 +128,17 @@ bool Snapshot::HasContextSnapshot(Isolate* isolate, size_t index) {
   return index < num_contexts;
 }
 
+bool Snapshot::VersionIsValid(const v8::StartupData* data) {
+  char version[SnapshotImpl::kVersionStringLength];
+  memset(version, 0, SnapshotImpl::kVersionStringLength);
+  CHECK_LT(
+      SnapshotImpl::kVersionStringOffset + SnapshotImpl::kVersionStringLength,
+      static_cast<uint32_t>(data->raw_size));
+  Version::GetString(Vector<char>(version, SnapshotImpl::kVersionStringLength));
+  return strncmp(version, data->data + SnapshotImpl::kVersionStringOffset,
+                 SnapshotImpl::kVersionStringLength) == 0;
+}
+
 bool Snapshot::Initialize(Isolate* isolate) {
   if (!isolate->snapshot_available()) return false;
   RuntimeCallTimerScope rcs_timer(isolate,
@@ -600,13 +611,12 @@ Vector<const byte> SnapshotImpl::ExtractContextData(const v8::StartupData* data,
 }
 
 void SnapshotImpl::CheckVersion(const v8::StartupData* data) {
-  char version[kVersionStringLength];
-  memset(version, 0, kVersionStringLength);
-  CHECK_LT(kVersionStringOffset + kVersionStringLength,
-           static_cast<uint32_t>(data->raw_size));
-  Version::GetString(Vector<char>(version, kVersionStringLength));
-  if (strncmp(version, data->data + kVersionStringOffset,
-              kVersionStringLength) != 0) {
+  if (!Snapshot::VersionIsValid(data)) {
+    char version[kVersionStringLength];
+    memset(version, 0, kVersionStringLength);
+    CHECK_LT(kVersionStringOffset + kVersionStringLength,
+             static_cast<uint32_t>(data->raw_size));
+    Version::GetString(Vector<char>(version, kVersionStringLength));
     FATAL(
         "Version mismatch between V8 binary and snapshot.\n"
         "#   V8 binary version: %.*s\n"

src/snapshot/snapshot.h

@@ -91,6 +91,7 @@ class Snapshot : public AllStatic {
   static bool EmbedsScript(Isolate* isolate);
   V8_EXPORT_PRIVATE static bool VerifyChecksum(const v8::StartupData* data);
   static bool ExtractRehashability(const v8::StartupData* data);
+  static bool VersionIsValid(const v8::StartupData* data);
 
   // To be implemented by the snapshot source.
   static const v8::StartupData* DefaultSnapshotBlob();