Align page allocation hint in VirtualMemoryCage initialization

Bug: chromium:1263504
Change-Id: I32091478eb1662b72e0b9507e7cd17314cb277d7
Cq-Include-Trybots: luci.v8.try:v8_linux64_heap_sandbox_dbg_ng
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3247634Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Samuel Groß <saelo@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77588}

src/security/vm-cage.cc

@@ -308,10 +308,12 @@ bool V8VirtualMemoryCage::Initialize(v8::PageAllocator* page_allocator,
     // PA anyway uses MAP_JIT for V8 mappings. Further, we want to eventually
     // move JIT pages out of the cage, at which point we'd like to forbid
     // making pages inside the cage executable, and so don't want MAP_JIT.
-    void* hint = page_allocator->GetRandomMmapAddr();
+    Address hint = RoundDown(
+        reinterpret_cast<Address>(page_allocator->GetRandomMmapAddr()),
+        kVirtualMemoryCageAlignment);
     reservation_base_ = reinterpret_cast<Address>(page_allocator->AllocatePages(
-        hint, reservation_size, kVirtualMemoryCageAlignment,
-        PageAllocator::kNoAccess));
+        reinterpret_cast<void*>(hint), reservation_size,
+        kVirtualMemoryCageAlignment, PageAllocator::kNoAccess));
     if (!reservation_base_) {
       size /= 2;
     }