CVE-2026-68329

Received Received - Intake

Race Condition in AMD IOMMU Completion Handling

Publication date: 2026-08-10

Last updated on: 2026-08-17

Assigner: kernel.org

Description

In the Linux kernel, the following vulnerability has been resolved: iommu/amd: Wait for completion instead of returning early in iommu_completion_wait() need_sync is a per-IOMMU flag shared by all domains and devices behind that IOMMU. It is set whenever a command is queued with sync == true and cleared when a completion-wait (CWAIT) command is queued. However, a cleared need_sync only means that a covering CWAIT has been queued, not that all previously queued commands have actually completed in hardware. iommu_completion_wait() read need_sync locklessly and returned early when it was false. This breaks the "block until all previously queued commands have completed" contract in a multi-CPU scenario: CPU2: queue inv-B => need_sync = true CPU1: queue CWAIT(N); need_sync = false; then wait_on_sem(N) CPU2: read need_sync == false => return 0 (no wait!) CPU2 returns without waiting for any sequence number even though its inv-B may not have completed yet (CWAIT(N), queued after inv-B, has not been signaled). CPU2 then proceeds to, for example, free page-table pages while the IOMMU can still walk stale translations, opening a use-after-free window. This is a logical race in the meaning of the flag, not a memory-visibility issue, so barriers alone do not help. Fix it without losing the optimization of avoiding redundant CWAIT commands: take iommu->lock before testing need_sync, and when it is false do not return early but wait for the last allocated sequence number (cmd_sem_val). Since need_sync == false implies no sync command was queued after the last CWAIT, that CWAIT is FIFO-ordered after every not-yet-completed command, so waiting for its sequence number guarantees all prior commands (possibly queued by another CPU) have completed. The common path with pending work is unchanged and no extra hardware command is issued.

CVSS Scores

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Meta Information

Published

2026-08-10

Last Modified

2026-08-17

Generated

2026-08-30

AI Q&A

2026-08-10

EPSS Evaluated

2026-08-29

NVD

CVE-2026-68329

EUVD

EUVD-2026-55430

Affected Vendors & Products

Vendor	Product	Version / Range
linux	linux_kernel	*

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-UNKNOWN

Attack-Flow Graph

Executive Summary

This is a race condition in the Linux kernel's IOMMU (Input-Output Memory Management Unit) driver for AMD systems. The issue occurs in the iommu_completion_wait() function, which is supposed to wait for all previously queued commands to complete before proceeding. However, due to a flawed check of the need_sync flag, the function may return early without waiting, allowing subsequent operations to proceed while the IOMMU is still processing older commands. This creates a use-after-free vulnerability where memory can be freed while the IOMMU is still using it.

Detection Guidance

This vulnerability is specific to the Linux kernel's IOMMU subsystem and requires kernel-level detection. There are no direct network or system commands to detect it as it is a race condition in the AMD IOMMU driver. Monitoring kernel logs for IOMMU-related errors or crashes may indicate exploitation or instability. Kernel developers recommend updating to a patched kernel version to resolve this issue.

Impact Analysis

This vulnerability could allow an attacker with local access to trigger a use-after-free condition, potentially leading to system crashes, privilege escalation, or arbitrary code execution. It affects systems using AMD IOMMU, particularly those running virtualized environments or with hardware virtualization enabled.

Compliance Impact

This vulnerability does not directly affect compliance with standards like GDPR or HIPAA as it pertains to a race condition in the Linux kernel's IOMMU subsystem, which could lead to use-after-free scenarios. Compliance implications would depend on how the affected system is used in a specific environment.

Mitigation Strategies

Update the Linux kernel to a patched version that resolves CVE-2026-68329. This vulnerability is specific to the AMD IOMMU driver in the Linux kernel, so applying the official kernel patch is the primary mitigation step.

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