CVE-2026-74573: iommu/arm-smmu-v3-iommufd: Require exactly one Stream ID for a vDEVICE

CVE-2026-74573: iommu/arm-smmu-v3-iommufd: Require exactly one Stream ID for a vDEVICE

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

iommu/arm-smmu-v3-iommufd: Require exactly one Stream ID for a vDEVICE

arm_vsmmu_vsid_to_sid() maps a guest's vSID to a single physical Stream ID
taken from master->streams[0], assuming a device has exactly one stream. A
device with several streams gets only its first one mapped, so a guest vSID
invalidation cannot reach the others' ATC and IOTLB entries; a device with
none makes master->streams a ZERO_SIZE_PTR, read out of bounds.

Add an arm_vsmmu_vdevice_init() op to reject the vDEVICE with -EOPNOTSUPP
when master->num_streams is not one, rather than mapping it silently.

The Linux kernel CVE team has assigned CVE-2026-74573 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.13 with commit d68beb276ba26cec47350a6d468e967673ee0c56 and fixed in 6.18.44 with commit 3808bab5d95ae79e333e11f6a73d178e084c645d
	Issue introduced in 6.13 with commit d68beb276ba26cec47350a6d468e967673ee0c56 and fixed in 7.1.8 with commit 0acbc621341aca4eb94d9c2f43e1ab273ff088f0
	Issue introduced in 6.13 with commit d68beb276ba26cec47350a6d468e967673ee0c56 and fixed in 7.2-rc6 with commit c3b8ee84a965058b41275069d4696f37a8b14bf6

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-74573
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/3808bab5d95ae79e333e11f6a73d178e084c645d
	https://git.kernel.org/stable/c/0acbc621341aca4eb94d9c2f43e1ab273ff088f0
	https://git.kernel.org/stable/c/c3b8ee84a965058b41275069d4696f37a8b14bf6