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<p>Hello,</p>
<p>Edge Vuln Research just dropped the amazing named "Super Duper
Secure Mode" [1]---an interesting albeit slightly provocative
statement they make in the announcement is that JITs may not be
worth it for security-sensitive users, since they account for
about half the bugs in V8 (Chromium's JS engine) and their new
research shows that disabling JITs, despite the huge performance
regressions in traditional JS benchmarks, is rarely noticeable in
real-life. I don't think tbb is new to clamping down JS (for
security-sensitive users), but this idea of disabling JITs might
be interesting to look into*.</p>
<p>First, taking a step back, recall that modern browsers execute JS
by converting it into bytecode and then using an interpreter to
execute, and functions that are "hot" (executed many times) are
recompiled using a JIT to produce faster code. This is super
simplified, see [2] for a more technical overview of how this
works in Firefox.<br>
</p>
<p>I think this idea can be used to improve the Tor Browser,</p>
<ol>
<li>we can disable JITs in "Safer" mode which would reduce
usability but improve security; and</li>
<li>we can enable JS and disable JITs in "Safest" mode which would
reduce significantly improve usability but degrade security.</li>
</ol>
<p>On a more meta note, this wouldn't be hard to implement, Firefox
has prefs to enable and disable this stuff, and @freddyb's tweet
[3] seems to confirm this intuition.<br>
</p>
<p>What do y'all think?</p>
<p>Best,<br>
Sanketh</p>
<p>*disabling JITs was discussed in the tor issue tracker 4 years
ago [4] but most of the then concerns (like changing build
settings) seem to have been resolved and JITs are now enabled
across the browser (they were not enabled for content back then)
and so this, I feel, can use fresh eyes.</p>
<p>[1]:
<a class="moz-txt-link-freetext" href="https://microsoftedge.github.io/edgevr/posts/Super-Duper-Secure-Mode/">https://microsoftedge.github.io/edgevr/posts/Super-Duper-Secure-Mode/</a><br>
[2]:
<a class="moz-txt-link-freetext" href="https://hacks.mozilla.org/2020/11/warp-improved-js-performance-in-firefox-83/">https://hacks.mozilla.org/2020/11/warp-improved-js-performance-in-firefox-83/</a><br>
[3]: <a class="moz-txt-link-freetext" href="https://twitter.com/freddyb/status/1423020386560712705?s=20">https://twitter.com/freddyb/status/1423020386560712705?s=20</a><br>
[4]: <a class="moz-txt-link-freetext" href="https://gitlab.torproject.org/legacy/trac/-/issues/21011">https://gitlab.torproject.org/legacy/trac/-/issues/21011</a></p>
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