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From: Juergen Gross <jgross@suse.com>
To: "Roger Pau Monné" <roger.pau@citrix.com>
Cc: xen-devel@lists.xenproject.org, linux-block@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	Stefano Stabellini <sstabellini@kernel.org>,
	Jens Axboe <axboe@kernel.dk>, Jan Beulich <jbeulich@suse.com>
Subject: Re: [PATCH v2 2/3] xen/blkfront: don't take local copy of a request from the ring page
Date: Fri, 9 Jul 2021 15:54:19 +0200	[thread overview]
Message-ID: <57f50e6f-4fc4-7318-9f7f-c5b4e0e63487@suse.com> (raw)
In-Reply-To: <YOgPCZbEF+t5DN+G@Air-de-Roger>


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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.
> 

...

>> @@ -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

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  reply	other threads:[~2021-07-09 13:54 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-08 12:43 [PATCH v2 0/3] xen: harden blkfront against malicious backends Juergen Gross
2021-07-08 12:43 ` [PATCH v2 1/3] xen/blkfront: read response from backend only once Juergen Gross
2021-07-09  8:33   ` Roger Pau Monné
2021-07-08 12:43 ` [PATCH v2 2/3] xen/blkfront: don't take local copy of a request from the ring page Juergen Gross
2021-07-09  8:55   ` Roger Pau Monné
2021-07-09 13:54     ` Juergen Gross [this message]
2021-07-08 12:43 ` [PATCH v2 3/3] xen/blkfront: don't trust the backend response data blindly Juergen Gross
2021-07-08 13:11   ` Jan Beulich
2021-07-08 13:14     ` Juergen Gross
2021-07-09  9:42   ` Roger Pau Monné
2021-07-09 13:58     ` Juergen Gross
2021-07-09 11:09   ` kernel test robot
2021-07-30 10:08   ` Juergen Gross
2021-07-30 10:31     ` Juergen Gross
2021-07-08 14:22 ` [PATCH v2 0/3] xen: harden blkfront against malicious backends Konrad Rzeszutek Wilk
2021-07-08 14:39   ` Juergen Gross
2021-07-10  1:18     ` Marek Marczykowski-Górecki

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