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Date: Wed, 4 Oct 2023 00:51:56 +0200
From: Solar Designer <>
Subject: Re: Xen Security Advisory 439 v1 (CVE-2023-20588) - x86/AMD: Divide speculative information leak

On Tue, Oct 03, 2023 at 03:02:41PM -0700, Jean Luc Picard wrote:
> Hi, just dropping in, is this the kind of thing to where the userspace &
> kernel layers need mitigation until there's microcode mitigation?

In general, kind of yes - it could have been that kind of thing.

More specifically, no - in this case, only kernel and hypervisor
and system configuration (disable SMT) mitigations are expected.  No
userspace mitigations, other than maybe specific algorithms avoiding
integer divide operations based on secrets where they can.  While AMD
maybe could fix this in microcode (or maybe not, or maybe with
unacceptable performance penalty), they expressed no plans to do so.

> On Tue, Oct 3, 2023 at 2:46???PM Jeremy Stanley <> wrote:
> > On 2023-10-03 22:37:08 +0100 (+0100), Andrew Cooper wrote:
> > [...]
> > > If you have a proposal for how you'd prefer it to be done, I'll see what
> > > I can do.  Perhaps BCC oss-security, or just send out a second mail?
> >
> > When I send advisories, I prepare two basically identical E-mail
> > messages: one to the project's announcement list and one to
> > oss-security (signing both of them). It seems like this is the most
> > common approach to avoiding cross-posting between lists.

Andrew, sending a second message like Jeremy suggests works best.
Bcc currently isn't expected to work at all.  Thank you!

BTW, in this case I think the problem was actually for Xen's lists more
than for oss-security - you included xen-announce among the CC'ed lists,
and this means e.g. Demi Marie's reply was attempted to be posted to
there, while certainly not being a valid Xen announcement.  However, I
guess external messages to the announcement list are very easy to reject
on your side.  It's not so easy for us on oss-security because we've
setup some senders to bypass moderation, yet those people participate in
threads on other lists that might just happen to be CC'ed in here and
they might not notice that the rest of the sub-thread is moderated-out.

I'm not too concerned about this issue with Xen announcements in
particular - things have worked pretty well with these so far.


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