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 <[email protected]> > Reviewed-by: Jan Beulich <[email protected]>
Acked-by: Roger Pau Monné <[email protected]> Thanks! One unrelated comment below. > --- > V2: > - init variable to avoid potential compiler warning (Jan Beulich) > --- > drivers/block/xen-blkfront.c | 25 +++++++++++++++---------- > 1 file changed, 15 insertions(+), 10 deletions(-) > > diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c > index 86356014d35e..80701860870a 100644 > --- a/drivers/block/xen-blkfront.c > +++ b/drivers/block/xen-blkfront.c > @@ -546,7 +546,7 @@ static unsigned long blkif_ring_get_request(struct > blkfront_ring_info *rinfo, > rinfo->shadow[id].status = REQ_WAITING; > rinfo->shadow[id].associated_id = NO_ASSOCIATED_ID; > > - (*ring_req)->u.rw.id = id; > + rinfo->shadow[id].req.u.rw.id = id; > > return id; > } > @@ -554,11 +554,12 @@ static unsigned long blkif_ring_get_request(struct > blkfront_ring_info *rinfo, > static int blkif_queue_discard_req(struct request *req, struct > blkfront_ring_info *rinfo) > { > struct blkfront_info *info = rinfo->dev_info; > - struct blkif_request *ring_req; > + struct blkif_request *ring_req, *final_ring_req; > unsigned long id; > > /* Fill out a communications ring structure. */ > - id = blkif_ring_get_request(rinfo, req, &ring_req); > + id = blkif_ring_get_request(rinfo, req, &final_ring_req); > + ring_req = &rinfo->shadow[id].req; > > ring_req->operation = BLKIF_OP_DISCARD; > ring_req->u.discard.nr_sectors = blk_rq_sectors(req); > @@ -569,8 +570,8 @@ static int blkif_queue_discard_req(struct request *req, > struct blkfront_ring_inf > else > ring_req->u.discard.flag = 0; > > - /* Keep a private copy so we can reissue requests when recovering. */ > - rinfo->shadow[id].req = *ring_req; > + /* Copy the request to the ring page. */ > + *final_ring_req = *ring_req; > > return 0; > } > @@ -703,6 +704,7 @@ static int blkif_queue_rw_req(struct request *req, struct > blkfront_ring_info *ri > { > struct blkfront_info *info = rinfo->dev_info; > struct blkif_request *ring_req, *extra_ring_req = NULL; > + struct blkif_request *final_ring_req, *final_extra_ring_req = NULL; > unsigned long id, extra_id = NO_ASSOCIATED_ID; > bool require_extra_req = false; > int i; > @@ -747,7 +749,8 @@ static int blkif_queue_rw_req(struct request *req, struct > blkfront_ring_info *ri > } > > /* Fill out a communications ring structure. */ > - id = blkif_ring_get_request(rinfo, req, &ring_req); > + id = blkif_ring_get_request(rinfo, req, &final_ring_req); > + ring_req = &rinfo->shadow[id].req; > > num_sg = blk_rq_map_sg(req->q, req, rinfo->shadow[id].sg); > num_grant = 0; > @@ -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. Roger.
