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

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Message-ID: <20190911123316.GX4023@dhcp22.suse.cz>
Date:   Wed, 11 Sep 2019 14:33:16 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     "Michael S. Tsirkin" <mst@...hat.com>
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 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.

-- 
Michal Hocko
SUSE Labs