linux-kernel - Re: [PATCH v2 1/1] vfio/type1: Respect IOMMU reserved regions in vfio_test_domain

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: <dcd428a4-aaed-060e-34e0-69f931986ae6@linux.ibm.com>
Date:   Thu, 5 Jan 2023 11:06:31 -0500
From:   Matthew Rosato <mjrosato@...ux.ibm.com>
To:     Niklas Schnelle <schnelle@...ux.ibm.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>
Cc:     Jason Gunthorpe <jgg@...pe.ca>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        Pierre Morel <pmorel@...ux.ibm.com>,
        Christian Bornträger <borntraeger@...ux.ibm.com>
Subject: Re: [PATCH v2 1/1] vfio/type1: Respect IOMMU reserved regions in
 vfio_test_domain_fgsp()

On 1/4/23 10:42 AM, Niklas Schnelle wrote:
> Since commit cbf7827bc5dc ("iommu/s390: Fix potential s390_domain
> aperture shrinking") the s390 IOMMU driver uses reserved regions for the
> system provided DMA ranges of PCI devices. Previously it reduced the
> size of the IOMMU aperture and checked it on each mapping operation.
> On current machines the system denies use of DMA addresses below 2^32 for
> all PCI devices.
> 
> Usually mapping IOVAs in a reserved regions is harmless until a DMA
> actually tries to utilize the mapping. However on s390 there is
> a virtual PCI device called ISM which is implemented in firmware and
> used for cross LPAR communication. Unlike real PCI devices this device
> does not use the hardware IOMMU but inspects IOMMU translation tables
> directly on IOTLB flush (s390 RPCIT instruction). If it detects IOVA
> mappings outside the allowed ranges it goes into an error state. This
> error state then causes the device to be unavailable to the KVM guest.
> 
> Analysing this we found that vfio_test_domain_fgsp() maps 2 pages at DMA
> address 0 irrespective of the IOMMUs reserved regions. Even if usually
> harmless this seems wrong in the general case so instead go through the
> freshly updated IOVA list and try to find a range that isn't reserved,
> and fits 2 pages, is PAGE_SIZE * 2 aligned. If found use that for
> testing for fine grained super pages.
> 
> Fixes: 6fe1010d6d9c ("vfio/type1: DMA unmap chunking")
> Reported-by: Matthew Rosato <mjrosato@...ux.ibm.com>
> Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>

Thanks, this fixes the issue I'm seeing with ISM.

Reviewed-by: Matthew Rosato <mjrosato@...ux.ibm.com>