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
next prev parent 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
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