linux-kernel - Re: [PATCH v2] vhost: block speculation of translated descriptors

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Date:   Wed, 11 Sep 2019 09:03:10 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Jason Wang <jasowang@...hat.com>,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH v2] vhost: block speculation of translated descriptors

On Wed, Sep 11, 2019 at 02:33:16PM +0200, Michal Hocko wrote:
> On Wed 11-09-19 08:25:03, Michael S. Tsirkin wrote:
> > On Wed, Sep 11, 2019 at 02:16:28PM +0200, Michal Hocko wrote:
> > > On Wed 11-09-19 08:10:00, Michael S. Tsirkin wrote:
> > > > iovec addresses coming from vhost are assumed to be
> > > > pre-validated, but in fact can be speculated to a value
> > > > out of range.
> > > > 
> > > > Userspace address are later validated with array_index_nospec so we can
> > > > be sure kernel info does not leak through these addresses, but vhost
> > > > must also not leak userspace info outside the allowed memory table to
> > > > guests.
> > > > 
> > > > Following the defence in depth principle, make sure
> > > > the address is not validated out of node range.
> > > > 
> > > > Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> > > > Acked-by: Jason Wang <jasowang@...hat.com>
> > > > Tested-by: Jason Wang <jasowang@...hat.com>
> > > 
> > > no need to mark fo stable? Other spectre fixes tend to be backported
> > > even when the security implications are not really clear. The risk
> > > should be low and better to be covered in case.
> > 
> > This is not really a fix - more a defence in depth thing,
> > quite similar to e.g.  commit b3bbfb3fb5d25776b8e3f361d2eedaabb0b496cd
> > x86: Introduce __uaccess_begin_nospec() and uaccess_try_nospec
> > in scope.
> >
> > That one doesn't seem to be tagged for stable. Was it queued
> > there in practice?
> 
> not marked for stable but it went in. At least to 4.4.

So I guess the answer is I don't know. If you feel it's
justified, then sure, feel free to forward.

-- 
MST