CVE-2026-45894
iommu/vt-d: Clear Present bit before tearing down PASID entry
Description
In the Linux kernel, the following vulnerability has been resolved: iommu/vt-d: Clear Present bit before tearing down PASID entry The Intel VT-d Scalable Mode PASID table entry consists of 512 bits (64 bytes). When tearing down an entry, the current implementation zeros the entire 64-byte structure immediately using multiple 64-bit writes. Since the IOMMU hardware may fetch these 64 bytes using multiple internal transactions (e.g., four 128-bit bursts), updating or zeroing the entire entry while it is active (P=1) risks a "torn" read. If a hardware fetch occurs simultaneously with the CPU zeroing the entry, the hardware could observe an inconsistent state, leading to unpredictable behavior or spurious faults. Follow the "Guidance to Software for Invalidations" in the VT-d spec (Section 6.5.3.3) by implementing the recommended ownership handshake: 1. Clear only the 'Present' (P) bit of the PASID entry. 2. Use a dma_wmb() to ensure the cleared bit is visible to hardware before proceeding. 3. Execute the required invalidation sequence (PASID cache, IOTLB, and Device-TLB flush) to ensure the hardware has released all cached references. 4. Only after the flushes are complete, zero out the remaining fields of the PASID entry. Also, add a dma_wmb() in pasid_set_present() to ensure that all other fields of the PASID entry are visible to the hardware before the Present bit is set.
INFO
Published Date :
May 27, 2026, 2:17 p.m.
Last Modified :
May 30, 2026, 11:17 a.m.
Remotely Exploit :
No
Source :
416baaa9-dc9f-4396-8d5f-8c081fb06d67
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | HIGH | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 |
Solution
- Clear the 'Present' (P) bit of the PASID entry.
- Use dma_wmb() to ensure the cleared bit is visible to hardware.
- Execute invalidation sequences (PASID cache, IOTLB, Device-TLB flush).
- Zero out the remaining fields of the PASID entry after flushes.
References to Advisories, Solutions, and Tools
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CVE-2026-45894.
CWE - Common Weakness Enumeration
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specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-45894 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
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approaches employed by adversaries to exploit the CVE-2026-45894
weaknesses.
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CVE Modified by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
May. 30, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H -
New CVE Received by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
May. 27, 2026
Action Type Old Value New Value Added Description In the Linux kernel, the following vulnerability has been resolved: iommu/vt-d: Clear Present bit before tearing down PASID entry The Intel VT-d Scalable Mode PASID table entry consists of 512 bits (64 bytes). When tearing down an entry, the current implementation zeros the entire 64-byte structure immediately using multiple 64-bit writes. Since the IOMMU hardware may fetch these 64 bytes using multiple internal transactions (e.g., four 128-bit bursts), updating or zeroing the entire entry while it is active (P=1) risks a "torn" read. If a hardware fetch occurs simultaneously with the CPU zeroing the entry, the hardware could observe an inconsistent state, leading to unpredictable behavior or spurious faults. Follow the "Guidance to Software for Invalidations" in the VT-d spec (Section 6.5.3.3) by implementing the recommended ownership handshake: 1. Clear only the 'Present' (P) bit of the PASID entry. 2. Use a dma_wmb() to ensure the cleared bit is visible to hardware before proceeding. 3. Execute the required invalidation sequence (PASID cache, IOTLB, and Device-TLB flush) to ensure the hardware has released all cached references. 4. Only after the flushes are complete, zero out the remaining fields of the PASID entry. Also, add a dma_wmb() in pasid_set_present() to ensure that all other fields of the PASID entry are visible to the hardware before the Present bit is set. Added Reference https://git.kernel.org/stable/c/75ed00055c059dedc47b5daaaa2f8a7a019138ff Added Reference https://git.kernel.org/stable/c/821807c167b7b48a41b95b6607c6b9f97600f7d9 Added Reference https://git.kernel.org/stable/c/949d71666e9dd19f21e7b4b53a88cd2c5b902858 Added Reference https://git.kernel.org/stable/c/a84d30e8d2bacd21782a6481158b7c9c552f4868