> On Feb 19, 2018, at 10:53 AM, Guillaume Emont <guijem...@igalia.com> wrote: > > Hi Keith, > > We at Igalia have been trying to provide a better story for 32-bit > platforms, in particular for Armv7 and MIPS. These platforms are very > important to us, and disabling JIT renders many use cases impossible.
What use cases? I realize that having a JIT is good for marketing, but it’s better to have a stable and well-maintained interpreter than a decrepit JIT. Right now the 32-bit JIT is basically unmaintained. > We > want to continue this effort to support these platforms. We have been > short on resources for that effort, which is why we did not realize > early enough that more mitigation was needed for 32-bit platforms. We > now have grown our team dedicated to this and we are hopeful that we > will avoid that kind of issue in the future. I feel like I’ve heard this exact story before. Every time we say that there isn’t any effort going into 32-bit, y’all say that you’ll put more effort into it Real Soon Now. And then nothing happens, and we have the same conversation in 6 months. > > We are working on a plan to mitigate Spectre on 32-bit platforms. We > would welcome community feedback on that, as well as what kinds of > mitigations would be considered sufficient. > > Regarding your patch, I think you should note that some specific 32-bit > CPUs are immune to Spectre (at least the Raspberry Pi[1] and some > MIPS[2] devices), I think the deactivation should be done at run-time > for CPUs not on a white list. Keith’s main point is that the presence of 32-bit makes it harder to implement mitigations for 64-bit. I don’t think it’s justifiable to hold back development of 64-bit Spectre mitigations because of a hardly-used and mostly-broken 32-bit JIT port that will be maintained by someone Real Soon Now. -Filip > > Best regards, > > Guilaume Emont and the Igalia compilers team > > [1] > https://www.raspberrypi.org/blog/why-raspberry-pi-isnt-vulnerable-to-spectre-or-meltdown/ > [2] > https://www.mips.com/blog/mips-response-on-speculative-execution-and-side-channel-vulnerabilities/ > > Quoting Keith Miller (2018-02-16 16:58:07) >> I recently created a patch to disable the 32-bit JITs by default. >> https://bugs.webkit.org/show_bug.cgi?id=182886. >> >> The last time this was discussed was before the discovery of Spectre. In the >> interim, there have been a number of changes made to JavaScriptCore in an >> attempt to mitigate Spectre. Nobody has proposed a mitigation plan for >> 32-bit WebKit. For example, pointer poisoning only works for 64-bit >> processors as they currently have a number of high bits that will never be >> set in a valid pointer. In 32-bit code the full address space is mappable so >> pointer poisoning is not guaranteed to be effective. >> >> Given the importance of developing mitigations for Spectre in a timely >> manner I think we should disable 32-bit JITs, in the near term, but more >> likely permanently. >> >> Thoughts? >> Keith >> _______________________________________________ >> webkit-dev mailing list >> webkit-dev@lists.webkit.org >> https://lists.webkit.org/mailman/listinfo/webkit-dev >> > _______________________________________________ > webkit-dev mailing list > webkit-dev@lists.webkit.org > https://lists.webkit.org/mailman/listinfo/webkit-dev _______________________________________________ webkit-dev mailing list webkit-dev@lists.webkit.org https://lists.webkit.org/mailman/listinfo/webkit-dev
