Messages in this thread | | | Subject | Re: [PATCH v2 2/3] xen/blkfront: don't take local copy of a request from the ring page | From | Juergen Gross <> | Date | Fri, 9 Jul 2021 15:54:19 +0200 |
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On 09.07.21 10:55, Roger Pau Monné wrote: > On Thu, Jul 08, 2021 at 02:43:44PM +0200, Juergen Gross wrote: >> In order to avoid a malicious backend being able to influence the local >> copy of a request build the request locally first and then copy it to >> the ring page instead of doing it the other way round as today. >> >> Signed-off-by: Juergen Gross <jgross@suse.com> >> Reviewed-by: Jan Beulich <jbeulich@suse.com> > > Acked-by: Roger Pau Monné <roger.pau@citrx.com> > > Thanks! > > One unrelated comment below. >
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>> @@ -798,7 +801,9 @@ static int blkif_queue_rw_req(struct request *req, struct blkfront_ring_info *ri >> ring_req->u.rw.nr_segments = num_grant; >> if (unlikely(require_extra_req)) { >> extra_id = blkif_ring_get_request(rinfo, req, >> - &extra_ring_req); >> + &final_extra_ring_req); >> + extra_ring_req = &rinfo->shadow[extra_id].req; > > I'm slightly confused about this extra request stuff because I cannot > find any check that asserts we have two empty slots on the ring before > getting here (I only see a RING_FULL check in blkif_queue_rq). > > This is AFAIK only used on Arm when guest page size > 4KB.
I agree that this is a bug and should be fixed.
Juergen [unhandled content-type:application/pgp-keys][unhandled content-type:application/pgp-signature] | |