Code inside strength reduction can incorrectly prove that we know what lastIndex is

• Component: JavaScriptCore
• Status: RESOLVED FIXED

[Lukas Bernhard]

According to https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp/exec RegExp.prototype.exec() should return null or an array.
However, with FTL Regex.exec() might return (at least one) other type.
Filing as security because v8's typer speculates the type to always be array or null and I'm not sure whether similar assumptions are made in FTL code.
Tested on 29c8d02c3b11c096cc67d89e5cfe8c16be42b3b7 (Fri Sep 24 09:39:18 2021 +0000)

./Release/bin/jsc --validateOptions=true --useConcurrentJIT=false --useConcurrentGC=false --thresholdForJITSoon=10 --thresholdForJITAfterWarmUp=10 --thresholdForOptimizeAfterWarmUp=100 --thresholdForOptimizeAfterLongWarmUp=100 --thresholdForOptimizeSoon=100 --thresholdForFTLOptimizeAfterWarmUp=1000 --thresholdForFTLOptimizeSoon=1000 --validateBCE=true --useFTLJIT=true diff.js

function main() {
  let v41 = 2;
  
  const v31 = RegExp(1,..."global");
  for (let v36 = 0; v36 < 100; v36++) {
      function v37() {
          v41 = v31.exec("-1");
      }   
      v37();
  }
  
  print(v41); // prints 1 with FLT, null without FLT. also null in v8
}
main();

[Radar WebKit Bug Importer]

<rdar://problem/83543699>

[Saam Barati]

Thanks, this is a great bug.

[Saam Barati]

If the RegExp node is a constant, we can't claim that we know what lastIndex is if we don't see a SetRegExpObjectLastIndex node.

[Saam Barati]

*** Bug 230934 has been marked as a duplicate of this bug. ***

[Saam Barati]

Created attachment 439562 [details]
patch

[Mark Lam]

Comment on attachment 439562 [details]
patch

r=me

[EWS]

Committed r283232 (242274@main): <https://commits.webkit.org/242274@main>

All reviewed patches have been landed. Closing bug and clearing flags on attachment 439562 [details].