linux-kernel - Re: [RFC 1/2] virtio_console: Add support for DMA memory allocation

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: <CAJK669bhVfgnxuF6wVtdnzs2bgiJ2HzgwfWw4uZ=EqTdm43Jow@mail.gmail.com>
Date:	Wed, 5 Sep 2012 20:15:36 +0200
From:	Sjur Brændeland <sjurbren@...il.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Ohad Ben-Cohen <ohad@...ery.com>
Cc:	Amit Shah <amit.shah@...hat.com>, linux-kernel@...r.kernel.org,
	Linus Walleij <linus.walleij@...aro.org>,
	virtualization@...ts.linux-foundation.org,
	Sjur Brændeland <sjur.brandeland@...ricsson.com>
Subject: Re: [RFC 1/2] virtio_console: Add support for DMA memory allocation

Hi Michael.

>> If the device then asks for VIRTIO_CONSOLE_F_DMA_MEM
>> when DMA is not supported, virtio will do BUG_ON() from
>> virtio_check_driver_offered_feature().
>>
>> Is this acceptable or should we add a check in virtcons_probe()
>> and let the probing fail instead?
>>
>> E.g:
>>       /* Refuse to bind if F_DMA_MEM request cannot be met */
>>       if (!VIRTIO_CONSOLE_HAS_DMA &&
>>           (vdev->config->get_features(vdev) & (1 << VIRTIO_CONSOLE_F_DMA_MEM))){
>>               dev_err(&vdev->dev,
>>                       "DMA_MEM requested, but arch does not support DMA\n");
>>               err = -EINVAL;
>>               goto fail;
>>       }
>>
>> Regards,
>> Sjur
>
> Failing probe would be cleaner. But there is still a problem:
> old driver will happily bind to that device and then
> fail to work, right?

Not just fail to work, the kernel will panic on the BUG_ON().
Remoteproc gets the virtio configuration from firmware loaded
from user space. So this type of problem might be triggered
for other virtio drivers as well.

> virtio pci has revision id for this, but remoteproc doesn't
> seem to have anything similar. Or did I miss it?

No there are currently no sanity check of
virtio type and feature bits in remoteproc.
One option may be to add this...

> If not -
> we probably need to use a different
> device id, and not a feature bit.

But if I create a new virtio console type, remoteproc
could still call the existing virtio_console with random
bad feature bits, causing kernel panic.

Even if we fix this particular problem, the general problem
still exists: bogus virtio declarations in remoteproc's firmware
may cause BUG_ON(). (Note the fundamental difference
between visualizations and remoteproc. For remoteproc
the virtio configuration comes from binaries loaded from
user space).

So maybe we should look for a more generic solution, e.g.
changing virtio probe functionality so that devices with
bad feature bits will not trigger BUG_ON(), but rather refuse
to bind the driver.

Regards,
Sjur
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/