Re: [PATCH v1 5/8] dma: Use size for swiotlb boundary checks

On 6/2/2021 6:48 PM, Konrad Rzeszutek Wilk wrote:

On Wed, Jun 02, 2021 at 05:41:30PM -0700, Andi Kleen wrote:

quoted

swiotlb currently only uses the start address of a DMA to check if something
is in the swiotlb or not. But with virtio and untrusted hosts the host
could give some DMA mapping that crosses the swiotlb boundaries,
potentially leaking or corrupting data. Add size checks to all the swiotlb
checks and reject any DMAs that cross the swiotlb buffer boundaries.

I seem to be only CC-ed on this and #7, so please bear with me.

You weren't cc'ed originally so if you get partial emails it must be 
through some list.

But could you explain to me why please:

commit daf9514fd5eb098d7d6f3a1247cb8cc48fc94155 (swiotlb/stable/for-linus-5.12)
Author: Martin Radev [off-list ref]
Date:   Tue Jan 12 16:07:29 2021 +0100

     swiotlb: Validate bounce size in the sync/unmap path

does not solve the problem as well?

Thanks. I missed that patch, race condition.

One major difference of my patch is that it supports an error return, 
which allows virtio to error out. This is important in virtio because 
otherwise you'll end up with uninitialized memory on the target without 
any indication. This uninitialized memory could be an potential attack 
vector on the guest memory, e.g. if the attacker finds some way to echo 
it out again.

But the error return could be added to your infrastructure too and what 
would make this patch much shorter. I'll take a look at that.

-Andi





_______________________________________________
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization