CVE-2026-68438: In the Linux kernel, the following vulnerability has been resolved: smp: Make CSD lock acquisition atomic for debug mode Commit b0473dcd4b1d ("smp: ...

Description

In the Linux kernel, the following vulnerability has been resolved: smp: Make CSD lock acquisition atomic for debug mode Commit b0473dcd4b1d ("smp: Improve smp_call_function_single() CSD-lock diagnostics") changed smp_call_function_single() so that, when CSD lock debugging is enabled, async !wait calls use the destination CPU csd_data. That improves diagnostics, but it also removes the single-writer property that made the old csd_lock() safe: multiple CPUs can now prepare the same destination CPU CSD concurrently. csd_lock() currently waits for CSD_FLAG_LOCK to clear and then sets the bit with a non-atomic read-modify-write. Two senders can both see an unlocked CSD, set the bit, overwrite the callback fields, and enqueue the same llist node. Re-adding a node that is already the queue head can make node->next point to itself, leaving the target CPU stuck walking call_single_queue. Later synchronous work, such as a TLB shootdown, can then remain queued and trigger soft-lockup warnings or panics. Keep the single csd_lock() implementation, but when CSD lock debugging is enabled, acquire CSD_FLAG_LOCK with try_cmpxchg_acquire(). This makes the destination CPU CSD a real atomic lock in the only configuration where it can be shared by multiple remote senders, while preserving the existing non-debug fast path.

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

Vendor	Product	Versions
Linux	Linux	>= b0473dcd4b1d7e2e44947e7ac1820c73a268821a, < 282d220bae5fbfc90cf0e3d5b5e42c00ad79f989; >= b0473dcd4b1d7e2e44947e7ac1820c73a268821a, < 35551efb155e3b83445a6c3f66cb498d5efc182c
Linux	Linux	7.1

References

Timeline

Published: Aug 12, 2026
Last Modified: Aug 12, 2026
Status: Received

Frequently Asked Questions

What is CVE-2026-68438?

In the Linux kernel, the following vulnerability has been resolved: smp: Make CSD lock acquisition atomic for debug mode Commit b0473dcd4b1d ("smp: Improve smp_call_function_single() CSD-lock diagnostics") changed smp_call_function_single() so that, when CSD lock debugging is enabled, async !wait calls use the destination CPU csd_data. That improves diagnostics, but it also removes the single-writer property that made the old csd_lock() safe: multiple CPUs can now prepare the same destination CPU CSD concurrently. csd_lock() currently waits for CSD_FLAG_LOCK to clear and then sets the bit with a non-atomic read-modify-write. Two senders can both see an unlocked CSD, set the bit, overwrite the callback fields, and enqueue the same llist node. Re-adding a node that is already the queue head can make node->next point to itself, leaving the target CPU stuck walking call_single_queue. Later synchronous work, such as a TLB shootdown, can then remain queued and trigger soft-lockup warnings or panics. Keep the single csd_lock() implementation, but when CSD lock debugging is enabled, acquire CSD_FLAG_LOCK with try_cmpxchg_acquire(). This makes the destination CPU CSD a real atomic lock in the only configuration where it can be shared by multiple remote senders, while preserving the existing non-debug fast path.

How severe is CVE-2026-68438?

Severity scoring for CVE-2026-68438 is pending analysis.

How do I fix CVE-2026-68438?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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