linux-kernel - Re: [PATCH v1 2/6] virtio console: Harden port adding

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <87k018p4xs.fsf@ubik.fi.intel.com>
Date:   Fri, 27 Jan 2023 13:55:43 +0200
From:   Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        jasowang@...hat.com, virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, elena.reshetova@...el.com,
        kirill.shutemov@...ux.intel.com, Andi Kleen <ak@...ux.intel.com>,
        Amit Shah <amit@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        alexander.shishkin@...ux.intel.com
Subject: Re: [PATCH v1 2/6] virtio console: Harden port adding

"Michael S. Tsirkin" <mst@...hat.com> writes:

> On Thu, Jan 19, 2023 at 10:13:18PM +0200, Alexander Shishkin wrote:
>> When handling control messages, instead of peeking at the device memory
>> to obtain bits of the control structure,
>
> Except the message makes it seem that we are getting data from
> device memory, when we do nothing of the kind.

We can be, see below.

>> take a snapshot of it once and
>> use it instead, to prevent it from changing under us. This avoids races
>> between port id validation and control event decoding, which can lead
>> to, for example, a NULL dereference in port removal of a nonexistent
>> port.
>> 
>> The control structure is small enough (8 bytes) that it can be cached
>> directly on the stack.
>
> I still have no real idea why we want a copy here.
> If device can poke anywhere at memory then it can crash kernel anyway.
> If there's a bounce buffer or an iommu or some other protection
> in place, then this memory can no longer change by the time
> we look at it.

We can have shared pages between the host and guest without bounce
buffers in between, so they can be both looking directly at the same
page.

Regards,
--
Alex