[wasm] 32-bit platforms: lower kV8MaxWasmMemoryPages by 1

To make sure that Wasm memories don't exceed JSArrayBuffer size.
This change shouldn't affect real-world modules, because finding
enough contiguous address space to allocate that much memory is
virtually impossible anyway.

Fixed: chromium:1242339
Change-Id: I68873796b9afb798cb1a64e5e1acc495cf509159
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3328783
Auto-Submit: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78336}

src/builtins/typed-array-createtypedarray.tq

@@ -292,7 +292,7 @@ transitioning macro ConstructByArrayBuffer(implicit context: Context)(
       // in the step 12 branch.
       newByteLength = bufferByteLength - offset;
       newLength = elementsInfo.CalculateLength(newByteLength)
-          otherwise IfInvalidOffset;
+          otherwise IfInvalidLength;
 
       // 12. Else,
     } else {

src/objects/js-array-buffer.cc

@@ -91,6 +91,7 @@ void JSArrayBuffer::Attach(std::shared_ptr<BackingStore> backing_store) {
     // invariant that their byte_length field is always 0.
     set_byte_length(0);
   } else {
+    CHECK_LE(backing_store->byte_length(), kMaxByteLength);
     set_byte_length(backing_store->byte_length());
   }
   set_max_byte_length(backing_store->max_byte_length());

src/wasm/wasm-engine.cc

@@ -1649,6 +1649,9 @@ WasmCodeManager* GetWasmCodeManager() {
 
 // {max_mem_pages} is declared in wasm-limits.h.
 uint32_t max_mem_pages() {
+  static_assert(
+      kV8MaxWasmMemoryPages * kWasmPageSize <= JSArrayBuffer::kMaxByteLength,
+      "Wasm memories must not be bigger than JSArrayBuffers");
   STATIC_ASSERT(kV8MaxWasmMemoryPages <= kMaxUInt32);
   return std::min(uint32_t{kV8MaxWasmMemoryPages}, FLAG_wasm_max_mem_pages);
 }

src/wasm/wasm-limits.h

@@ -40,7 +40,7 @@ constexpr size_t kV8MaxWasmDataSegments = 100000;
 // Also, do not use this limit to validate declared memory, use
 // kSpecMaxMemoryPages for that.
 constexpr size_t kV8MaxWasmMemoryPages = kSystemPointerSize == 4
-                                             ? 32768   // = 2 GiB
+                                             ? 32767   // = 2 GiB
                                              : 65536;  // = 4 GiB
 constexpr size_t kV8MaxWasmStringSize = 100000;
 constexpr size_t kV8MaxWasmModuleSize = 1024 * 1024 * 1024;  // = 1 GiB