[Backport] CVE-2024-0518: Type Confusion in V8

Cherry-pick of patch originally reviewed on
https://chromium-review.googlesource.com/c/v8/v8/+/5180369:
Merged: [codegen] Install BytecodeArray last in SharedFunctionInfo

Maglev assumes that when a SharedFunctionInfo has a BytecodeArray,
then it should also have FeedbackMetadata. However, this may not
hold with concurrent compilation when the SharedFunctionInfo is
re-compiled after being flushed. Here the BytecodeArray was installed
on the SFI before the FeedbackMetadata and a concurrent thread could
observe the BytecodeArray but not the FeedbackMetadata.

Drive-by: Reset the age field before setting the BytecodeArray as
well. This ensures that the concurrent marker will not observe the
old age for the new BytecodeArray.

Bug: chromium:1507412
(cherry picked from commit 46cb67e3b296e50d7fda5a58233d18b9f3dab0d5)

Change-Id: Ide73ac1c6b0a68a1fcf847c8351ec65016e55762
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/5180369
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/branch-heads/12.0@{#28}
Cr-Branched-From: ed7b4caf1fb8184ad9e24346c84424055d4d430a-refs/heads/12.0.267@{#1}
Cr-Branched-From: 210e75b19db4352c9b78dce0bae11c2dc3077df4-refs/heads/main@{#90651}
Reviewed-on: https://codereview.qt-project.org/c/qt/qtwebengine-chromium/+/531979
Reviewed-by: Michal Klocek <michal.klocek@qt.io>

chromium/v8/src/codegen/compiler.cc

@@ -724,12 +724,12 @@ void InstallUnoptimizedCode(UnoptimizedCompilationInfo* compilation_info,
     }
 #endif  // V8_ENABLE_WEBASSEMBLY
 
-    shared_info->set_bytecode_array(*compilation_info->bytecode_array());
-    shared_info->set_age(0);
-
     Handle<FeedbackMetadata> feedback_metadata = FeedbackMetadata::New(
         isolate, compilation_info->feedback_vector_spec());
     shared_info->set_feedback_metadata(*feedback_metadata, kReleaseStore);
+
+    shared_info->set_age(0);
+    shared_info->set_bytecode_array(*compilation_info->bytecode_array());
   } else {
 #if V8_ENABLE_WEBASSEMBLY
     DCHECK(compilation_info->has_asm_wasm_data());