[log] Fix off-thread use of string.Get

Fixed: v8:12233
Change-Id: If23330e2edd6f4e2352800c145fc3ad5a360be5a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3162055
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76853}

src/logging/log-utils.cc

@@ -12,7 +12,10 @@
 #include "src/base/strings.h"
 #include "src/base/vector.h"
 #include "src/common/assert-scope.h"
+#include "src/common/globals.h"
+#include "src/execution/isolate-utils.h"
 #include "src/objects/objects-inl.h"
+#include "src/objects/string-inl.h"
 #include "src/strings/string-stream.h"
 #include "src/utils/version.h"
 
@@ -108,10 +111,12 @@ void Log::MessageBuilder::AppendString(String str,
   if (str.is_null()) return;
 
   DisallowGarbageCollection no_gc;  // Ensure string stays valid.
+  PtrComprCageBase cage_base = GetPtrComprCageBase(str);
+  SharedStringAccessGuardIfNeeded access_guard(str);
   int length = str.length();
   if (length_limit) length = std::min(length, *length_limit);
   for (int i = 0; i < length; i++) {
-    uint16_t c = str.Get(i);
+    uint16_t c = str.Get(i, cage_base, access_guard);
     if (c <= 0xFF) {
       AppendCharacter(static_cast<char>(c));
     } else {