Bug#1019855: Fwd: libc6: immediately crashes with SIGILL on 4th gen Intel Core CPUs (seems related to AVX2 instructions), bricking the whole system
On 2022-09-25 00:35, debian-bug-report@p0358.net wrote:
> Hello, sorry for delayed response, I've managed to collect and analyze a few
> coredump files with valid symbols (I installed libc6-dbg and dpkg-dev, and
> pointed gdb at Debian's debuginfod server, also used apt-get source to get
> the sources for libc6).
Thanks a lot for your work. With more data, it's way easier to
understand the issue.
> It seems there are at least 3-4 distinct places it crashes at, two places at
> memchr-avx2.S, one at strlen-avx2.S, and potentially one at
> syscall-template.S, although that last one may be just some kind of kill
> signal redirect.
The failing places in memchr-avx2.S and strlen-avx2.S points to BMI2
(bit manipulation instructions) which have been introduced in the AVX2
code, which should not have happened. The syscall-template.S is likely
code that catches the signal to display a message and then re-emit it.
> It does seem in case of this SIGILL there's no additional stack trace, also
> the path containing ".." seems to cause the source code resolution to fail,
> but still the debug symbols seem to show the file source and line, so it
> should hopefully help see what exactly fails.
>
> I'm yet to try rebooting with microcode package installed though (I'll soon
> check it and update on whether it helps, but even if it does, one without
> bootable system first won't get a chance to install it; I'm a bit curious
> how these changes did trigger this, given all these years it didn't happen
> to occur before)
I agree with you that this should be fixed without a microcode update, I
am going to report that issue upstream and we'll get the fix in the
Debian package.
Now that we understood the bug, I actually find strange that the
microcode update is fixing this, it looks like that the BMI2
instructions support has been added in a microcode update. Would it be
possible to give the output of /proc/cpuinfo with and without the
microcode update applied?
Regards
Aurelien
--
Aurelien Jarno GPG: 4096R/1DDD8C9B
aurelien@aurel32.net http://www.aurel32.net
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