Re: [PATCH V5 1/4] virtio_ring: validate used buffer length

From: Halil Pasic <pasic@linux.ibm.com>
To: Jason Wang <jasowang@redhat.com>
Cc: mst <mst@redhat.com>,
	virtualization <virtualization@lists.linux-foundation.org>,
	"Hetzelt, Felicitas" <f.hetzelt@tu-berlin.de>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	"kaplan, david" <david.kaplan@amd.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Stefan Hajnoczi <stefanha@redhat.com>,
	Stefano Garzarella <sgarzare@redhat.com>,
	Halil Pasic <pasic@linux.ibm.com>
Subject: Re: [PATCH V5 1/4] virtio_ring: validate used buffer length
Date: Mon, 22 Nov 2021 21:23:52 +0100	[thread overview]
Message-ID: <20211122212352.4a76232d.pasic@linux.ibm.com> (raw)
In-Reply-To: <CACGkMEu+9FvMsghyi55Ee5BxetP-YK9wh2oaT8OgLiY5+tV0QQ@mail.gmail.com>

On Mon, 22 Nov 2021 14:25:26 +0800
Jason Wang <jasowang@redhat.com> wrote:

> I think the fixes are:
> 
> 1) fixing the vhost vsock
> 2) use suppress_used_validation=true to let vsock driver to validate
> the in buffer length
> 3) probably a new feature so the driver can only enable the validation
> when the feature is enabled.

I'm not sure, I would consider a F_DEV_Y_FIXED_BUG_X a perfectly good
feature. Frankly the set of such bugs is device implementation
specific and it makes little sense to specify a feature bit
that says the device implementation claims to adhere to some
aspect of the specification. Also what would be the semantic
of not negotiating F_DEV_Y_FIXED_BUG_X?

On the other hand I see no other way to keep the validation
permanently enabled for fixed implementations, and get around the problem
with broken implementations. So we could have something like
VHOST_USED_LEN_STRICT.

Maybe, we can also think of 'warn and don't alter behavior' instead of
'warn' and alter behavior. Or maybe even not having such checks on in
production, but only when testing.

Regards,
Halil