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CVE-2026-90243
iommu/vt-d: Clear Present bit before tearing down copied context entry
Published 2026-09-17 (31 days ago) by the Linux kernel CNA. Subsystem drivers/iommu. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-90243 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | fixedDSA-6528-1 · 2026-09-29 · text | 6.12.111-1 | Update the kernel and reboot. DSA-6528-1 shipped the fix on 2026-09-29, in 6.12.111-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4817-1 · 2026-10-04 · text | 6.12.111-1~deb12u1 | Update the kernel and reboot. DLA-4817-1 shipped the fix on 2026-10-04, in 6.12.111-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
copied_context_tear_down() zeroes the 128-bit context entry with context_clear_entry() while the Present bit is still set, and only then issues the context-cache and IOTLB invalidations. This leaves a window in which hardware can fetch a torn entry, with some fields already zeroed while Present is still set, leading to unpredictable behaviour or spurious faults. While x86 provides strong write ordering, the compiler may reorder the writes to the two 64-bit halves of the entry, and the hardware fetch is not guaranteed to be atomic with respect to multiple CPU writes. There is no cacheline flush before the invalidation either, so on an IOMMU without coherent access to the context table the zeroed entry may not be visible to hardware at the point the invalidation is submitted. Apply the same ownership handshake described in the VT-d spec, Section 6.5.3.3 ("Guidance to Software for Invalidations"): clear only the Present bit, flush it out to the IOMMU, perform the invalidations, and only then zero the remainder of the entry.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
drivers/iommu/intel/iommu.c
- What this is
- INTEL IOMMU (VT-d)MAINTAINERS section matched on drivers/iommu/intel/ · iommu@lists.linux.dev · Supported
Check it on the machine
grep -w CONFIG_INTEL_IOMMU /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
Show whether Debian builds this, per release
Debian builds this, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed.
- bookwormYnot built on arm64/arm64, arm64/cloud-arm64, arm64/rt/arm64, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, i386/686, i386/686-pae, i386/rt/686-pae, ppc64el/powerpc64le
- trixieYnot built on arm64/arm64, arm64/arm64-16k, arm64/cloud-arm64, arm64/rt/arm64, armel/rpi, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, riscv64/riscv64, s390x/s390x
- forky, sidYnot built on arm64/arm64, arm64/arm64-16k, arm64/cloud-arm64, arm64/rt-arm64, armhf/armmp, armhf/armmp-lpae, loong64/loong64, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, riscv64/riscv64, s390x/s390x
- bookworm · linux-6.12Ynot built on arm64/arm64, arm64/arm64-16k, arm64/cloud-arm64, arm64/rt/arm64, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, ppc64el/powerpc64le, ppc64el/powerpc64le-64k
- Y
- built in where it is built at all; some flavours do not build it
- Build switch
- CONFIG_INTEL_IOMMU
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-09-17 (31 days ago)source
- CVSS
- 8.1 high
CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.16%, higher than 4.9% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- drivers/iommu
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.12 | 6.12.110 | 97750a8dce79 |
| 6.12 | 6.18.52 | 3c88cfedc776 |
| 6.12 | 7.2.6 | 6b822d18c33a |
| 6.12 | 7.3 | f532c57985b1 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4817-1 | 2026-10-04 | bookworm 6.12.111-1~deb12u1 | tracker |
| DSA-6528-1 | 2026-09-29 | trixie 6.12.111-1 | tracker |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:LAttack vector, local
- copied_context_tear_down() runs only from domain_context_mapping_one() and context_setup_pass_through() on crash-kernel attach (__iommu_probe_device → iommu_setup_default_domain → intel_iommu_attach_device or identity_domain_attach_dev). The trigger is in-flight PCIe DMA against a copied VT-d context, not a network protocol message.
- AC:HAttack complexity, high
- context_clear_entry() does two unordered 64-bit stores (context->lo=0, context->hi=0) while Present is still set, then flush_context/flush_iotlb. Hitting a torn Present=1 fetch depends on compiler store order, a non-atomic IOMMU 128-bit read, and/or a non-coherent IOMMU seeing unflushed writes—timing the attacker cannot reliably force.
- PR:NPrivileges required, none
- copy_translation_tables() in init_dmars() sets copied_tables only when is_kdump_kernel() and translation_pre_enabled(); copied_context_tear_down() then runs from __iommu_probe_device() with no capable() check. A DMA-capable PCIe device with leftover in-flight DMA needs no host account.
- UI:NUser interaction, none
- Crash-kernel PCI/IOMMU probing calls iommu_setup_default_domain() and then copied_context_tear_down() before the device driver probe/reset; no victim must mount a filesystem, open a file, or otherwise cooperate.
- S:CScope, changed
- A torn Present=1 copied context (old lo with ASR/TT intact, hi already zeroed so DID=0 and AW=0) lets VT-d translate that device’s DMA through the wrong domain-id and address-width against the copied page-table root, crossing the IOMMU DMA isolation boundary.
- C:HConfidentiality impact, high
- Hardware walking that torn copied context can map in-flight DMA reads to host physical pages outside the device’s intended domain, including crash-kernel memory beside the old tables copied by copy_translation_tables(), yielding cross-domain disclosure.
- I:HIntegrity impact, high
- The same Present=1 / DID=0 / AW=0 mix with the leftover ASR from the copied entry lets the device DMA-write host memory outside its assigned domain, an arbitrary write across the VT-d isolation boundary.
- A:HAvailability impact, high
- The fix documents unpredictable VT-d behaviour and spurious faults when hardware fetches the torn copied context in copied_context_tear_down(); those DMAR faults can oops, panic, or abort the crash dump.