linux-kernel - question about iommu_need

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-next>] [day] [month] [year] [list]

Message-ID: <20200219235516.zl44y7ydgqqja6x5@cantor>
Date:   Wed, 19 Feb 2020 16:55:16 -0700
From:   Jerry Snitselaar <jsnitsel@...hat.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: question about iommu_need_mapping

Is it possible for a device to end up with dev->archdata.iommu == NULL
on iommu_need_mapping in the following instance:

1. iommu_group has dma domain for default
2. device gets private identity domain in intel_iommu_add_device
3. iommu_need_mapping gets called with that device.
4. dmar_remove_one_dev_info sets dev->archdata.iommu = NULL via unlink_domain_info.
5. request_default_domain_for_dev exits after checking that group->default_domain
    exists, and group->default_domain->type is dma.
6. iommu_request_dma_domain_for_dev returns 0 from request_default_domain_for_dev
    and a private dma domain isn't created for the device.

The case I was seeing went away with commit 9235cb13d7d1 ("iommu/vt-d:
Allow devices with RMRRs to use identity domain"), because it changed
which domain the group and devices were using, but it seems like it is
still a possibility with the code. Baolu, you mentioned possibly
removing the domain switch. Commit 98b2fffb5e27 ("iommu/vt-d: Handle
32bit device with identity default domain") makes it sound like the
domain switch is required.

Regards,
Jerry