[sandbox] Enable the sandbox by default in V8 builds

This change makes the default configuration of standalone V8 builds
(again) reflect the default configuration of V8 in Chromium builds.

Bug: v8:10391
Change-Id: Ia98492a283772ebfde43f0edbfdff05319ac4352
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3913345Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Samuel Groß <saelo@chromium.org>
Cr-Commit-Position: refs/heads/main@{#83390}

BUILD.gn

@@ -521,9 +521,8 @@ if (v8_enable_sandbox == "") {
   # once that is enabled everywhere by default.
   # TODO(chromium:1325784) the sandbox is not currently supported in Chromium
   # on Fuchsia.
-  v8_enable_sandbox =
-      build_with_chromium && v8_enable_pointer_compression_shared_cage &&
-      v8_enable_external_code_space && target_os != "fuchsia"
+  v8_enable_sandbox = v8_enable_pointer_compression_shared_cage &&
+                      v8_enable_external_code_space && target_os != "fuchsia"
 }
 
 # Enable all available sandbox features if sandbox future is enabled.

src/api/api.cc

@@ -8128,12 +8128,12 @@ std::unique_ptr<v8::BackingStore> v8::ArrayBuffer::NewBackingStore(
     void* deleter_data) {
   CHECK_LE(byte_length, i::JSArrayBuffer::kMaxByteLength);
 #ifdef V8_ENABLE_SANDBOX
-  Utils::ApiCheck(
-      !data || i::GetProcessWideSandbox()->Contains(data),
-      "v8_ArrayBuffer_NewBackingStore",
-      "When the V8 Sandbox is enabled, ArrayBuffer backing stores must be "
-      "allocated inside the sandbox address space. Please use an appropriate "
-      "ArrayBuffer::Allocator to allocate these buffers.");
+  Utils::ApiCheck(!data || i::GetProcessWideSandbox()->Contains(data),
+                  "v8_ArrayBuffer_NewBackingStore",
+                  "When the V8 Sandbox is enabled, ArrayBuffer backing stores "
+                  "must be allocated inside the sandbox address space. Please "
+                  "use an appropriate ArrayBuffer::Allocator to allocate these "
+                  "buffers, or disable the sandbox.");
 #endif  // V8_ENABLE_SANDBOX
 
   std::unique_ptr<i::BackingStoreBase> backing_store =

src/objects/backing-store.cc

@@ -280,6 +280,14 @@ std::unique_ptr<BackingStore> BackingStore::Allocate(
       counters->array_buffer_new_size_failures()->AddSample(mb_length);
       return {};
     }
+#ifdef V8_ENABLE_SANDBOX
+    // Check to catch use of a non-sandbox-compatible ArrayBufferAllocator.
+    CHECK_WITH_MSG(GetProcessWideSandbox()->Contains(buffer_start),
+                   "When the V8 Sandbox is enabled, ArrayBuffer backing stores "
+                   "must be allocated inside the sandbox address space. Please "
+                   "use an appropriate ArrayBuffer::Allocator to allocate "
+                   "these buffers, or disable the sandbox.");
+#endif
   }
 
   auto result = new BackingStore(buffer_start,                  // start