| Message ID | 20210513100302.22027-4-jgross@suse.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | xen: harden frontends against malicious backends | expand |
On 13.05.2021 12:02, 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> with one remark/question: > @@ -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; Without setting final_extra_ring_req to NULL just like is done for extra_ring_req, ... > @@ -840,10 +845,10 @@ static int blkif_queue_rw_req(struct request *req, struct blkfront_ring_info *ri > if (setup.segments) > kunmap_atomic(setup.segments); > > - /* Keep a private copy so we can reissue requests when recovering. */ > - rinfo->shadow[id].req = *ring_req; > + /* Copy request(s) to the ring page. */ > + *final_ring_req = *ring_req; > if (unlikely(require_extra_req)) > - rinfo->shadow[extra_id].req = *extra_ring_req; > + *final_extra_ring_req = *extra_ring_req; ... are you sure all supported compilers will recognize the conditional use and not warn about use of a possibly uninitialized variable? Jan
On 17.05.21 16:01, Jan Beulich wrote: > On 13.05.2021 12:02, 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> > with one remark/question: > >> @@ -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; > > Without setting final_extra_ring_req to NULL just like is done for > extra_ring_req, ... > >> @@ -840,10 +845,10 @@ static int blkif_queue_rw_req(struct request *req, struct blkfront_ring_info *ri >> if (setup.segments) >> kunmap_atomic(setup.segments); >> >> - /* Keep a private copy so we can reissue requests when recovering. */ >> - rinfo->shadow[id].req = *ring_req; >> + /* Copy request(s) to the ring page. */ >> + *final_ring_req = *ring_req; >> if (unlikely(require_extra_req)) >> - rinfo->shadow[extra_id].req = *extra_ring_req; >> + *final_extra_ring_req = *extra_ring_req; > > ... are you sure all supported compilers will recognize the > conditional use and not warn about use of a possibly uninitialized > variable? Hmm, probably better safe than sorry. Will change it. Juergen
diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c index a8b56c153330..c6a05de4f15f 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; 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; + /* * Only the first request contains the scatter-gather * list. @@ -840,10 +845,10 @@ static int blkif_queue_rw_req(struct request *req, struct blkfront_ring_info *ri if (setup.segments) kunmap_atomic(setup.segments); - /* Keep a private copy so we can reissue requests when recovering. */ - rinfo->shadow[id].req = *ring_req; + /* Copy request(s) to the ring page. */ + *final_ring_req = *ring_req; if (unlikely(require_extra_req)) - rinfo->shadow[extra_id].req = *extra_ring_req; + *final_extra_ring_req = *extra_ring_req; if (new_persistent_gnts) gnttab_free_grant_references(setup.gref_head);
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> --- drivers/block/xen-blkfront.c | 25 +++++++++++++++---------- 1 file changed, 15 insertions(+), 10 deletions(-)