xen-devel.lists.xenproject.org archive mirror
 help / color / mirror / Atom feed
From: Jan Beulich <jbeulich@suse.com>
To: Juergen Gross <jgross@suse.com>
Cc: "Konrad Rzeszutek Wilk" <konrad.wilk@oracle.com>,
	"Roger Pau Monné" <roger.pau@citrix.com>,
	"Boris Ostrovsky" <boris.ostrovsky@oracle.com>,
	"Stefano Stabellini" <sstabellini@kernel.org>,
	"Jens Axboe" <axboe@kernel.dk>,
	xen-devel@lists.xenproject.org, linux-block@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/8] xen/blkfront: don't trust the backend response data blindly
Date: Mon, 17 May 2021 17:12:12 +0200	[thread overview]
Message-ID: <a19a13ba-a386-2808-ad85-338d47085fa6@suse.com> (raw)
In-Reply-To: <6095c4b9-a9bb-8a38-fb6c-a5483105b802@suse.com>

On 17.05.2021 16:23, Juergen Gross wrote:
> On 17.05.21 16:11, Jan Beulich wrote:
>> On 13.05.2021 12:02, Juergen Gross wrote:
>>> @@ -1574,10 +1580,16 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
>>>   	spin_lock_irqsave(&rinfo->ring_lock, flags);
>>>    again:
>>>   	rp = rinfo->ring.sring->rsp_prod;
>>> +	if (RING_RESPONSE_PROD_OVERFLOW(&rinfo->ring, rp)) {
>>> +		pr_alert("%s: illegal number of responses %u\n",
>>> +			 info->gd->disk_name, rp - rinfo->ring.rsp_cons);
>>> +		goto err;
>>> +	}
>>>   	rmb(); /* Ensure we see queued responses up to 'rp'. */
>>
>> I think you want to insert after the barrier.
> 
> Why? The relevant variable which is checked is "rp". The result of the
> check is in no way depending on the responses themselves. And any change
> of rsp_cons is protected by ring_lock, so there is no possibility of
> reading an old value here.

But this is a standard double read situation: You might check a value
and then (via a separate read) use a different one past the barrier.

Jan


  reply	other threads:[~2021-05-17 15:12 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-13 10:02 [PATCH 0/8] xen: harden frontends against malicious backends Juergen Gross
2021-05-13 10:02 ` [PATCH 1/8] xen: sync include/xen/interface/io/ring.h with Xen's newest version Juergen Gross
2021-05-13 10:02 ` [PATCH 2/8] xen/blkfront: read response from backend only once Juergen Gross
2021-05-17 13:50   ` Jan Beulich
2021-05-13 10:02 ` [PATCH 3/8] xen/blkfront: don't take local copy of a request from the ring page Juergen Gross
2021-05-17 14:01   ` Jan Beulich
2021-05-17 14:11     ` Juergen Gross
2021-05-13 10:02 ` [PATCH 4/8] xen/blkfront: don't trust the backend response data blindly Juergen Gross
2021-05-17 14:11   ` Jan Beulich
2021-05-17 14:23     ` Juergen Gross
2021-05-17 15:12       ` Jan Beulich [this message]
2021-05-17 15:22         ` Juergen Gross
2021-05-17 15:33           ` Jan Beulich
2021-07-08  5:47             ` Juergen Gross
2021-07-08  6:37               ` Jan Beulich
2021-07-08  6:40                 ` Juergen Gross
2021-07-08  6:52                   ` Jan Beulich
2021-07-08  6:56                     ` Juergen Gross
2021-05-13 10:02 ` [PATCH 5/8] xen/netfront: read response from backend only once Juergen Gross
2021-05-17 14:20   ` Jan Beulich
2021-05-17 14:24     ` Juergen Gross
2021-05-13 10:03 ` [PATCH 6/8] xen/netfront: don't read data from request on the ring page Juergen Gross
2021-05-17 15:08   ` Jan Beulich
2021-05-13 10:03 ` [PATCH 7/8] xen/netfront: don't trust the backend response data blindly Juergen Gross
2021-05-17 15:31   ` Jan Beulich
2021-05-13 10:03 ` [PATCH 8/8] xen/hvc: replace BUG_ON() with negative return value Juergen Gross
2021-05-13 10:16   ` Christophe Leroy
2021-05-13 10:20     ` Juergen Gross
2021-05-13 10:25   ` Greg Kroah-Hartman
2021-05-13 10:35     ` Juergen Gross
2021-05-21 10:43 ` [PATCH 0/8] xen: harden frontends against malicious backends Marek Marczykowski-Górecki

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=a19a13ba-a386-2808-ad85-338d47085fa6@suse.com \
    --to=jbeulich@suse.com \
    --cc=axboe@kernel.dk \
    --cc=boris.ostrovsky@oracle.com \
    --cc=jgross@suse.com \
    --cc=konrad.wilk@oracle.com \
    --cc=linux-block@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=roger.pau@citrix.com \
    --cc=sstabellini@kernel.org \
    --cc=xen-devel@lists.xenproject.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).