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Date: Tue, 25 Jul 2023 18:55:11 +0000
From: "alice" <alice@...ya.dev>
To: <oss-security@...ts.openwall.com>
Subject: Re: CVE-2023-20593: A use-after-free in AMD Zen2
Processors
On Tue Jul 25, 2023 at 6:30 PM UTC, Jeffrey Walton wrote:
> On Tue, Jul 25, 2023 at 2:14 PM Demi Marie Obenour
> <demi@...isiblethingslab.com> wrote:
> >
> > On Tue, Jul 25, 2023 at 06:12:44PM +0100, Eddie Chapman wrote:
> > > alice wrote:
> > > > this is a disaster of a security announcement from AMD. nothing is fixed
> > > > except for epyc. the only workaround anyone really has is the chicken bit,
> > > > thankfully.
> > >
> > > Yes, very disappointing. Pure speculation; perhaps they were planning on
> > > disclosing at the end of the year with full set of Microcode ready but
> > > something we don't know (yet) forced them to disclose early. Who knows.
> >
> > Does AMD make OS-loadable μcode patches available for client platforms,
> > or must all μcode loading on clients be done by the firmware? If the
> > latter, then it will take a very long time for clients to get patched,
> > even if AMD released the updates promptly. Also, server platforms can
> > usually reflash the firmware via the BMC, but client platforms do not
> > have this option.
>
> Related, Ubuntu released an updated amd64-microcode around (or before)
> 1:45 PM EST today. My Ubuntu machines have already been patched.
>
> I was kind of surprised to see how quickly it landed.
the updated amd64-microcode only contains the fixes published to linux-firmware,
which only affects epyc cpus, as noted. unless you're running epyc cpus (which
is slightly unlikely so i thought i'd mention it, but apologies if that is
indeed the case) you didn't actually receive any fix.
the latest kernel released today sets the chicken bit if no patched ucode is
loaded which also works to mitigate the issue.
(https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=522b1d69219d8f083173819fde04f994aa051a98)
you can test this by running the zenbleed reproduction, from
https://cmpxchg8b.com/files/zenbleed-v5.tar.gz
(if it outputs anything, you're vulnerable)
>
> Jeff
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