VYPR
← All advisories
Medium severity5.5NVD Advisory· Published Feb 28, 2024· Updated Jun 17, 2026

CVE-2021-46990

CVE-2021-46990

Description

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

powerpc/64s: Fix crashes when toggling entry flush barrier

The entry flush mitigation can be enabled/disabled at runtime via a debugfs file (entry_flush), which causes the kernel to patch itself to enable/disable the relevant mitigations.

However depending on which mitigation we're using, it may not be safe to do that patching while other CPUs are active. For example the following crash:

sleeper[15639]: segfault (11) at c000000000004c20 nip c000000000004c20 lr c000000000004c20

Shows that we returned to userspace with a corrupted LR that points into the kernel, due to executing the partially patched call to the fallback entry flush (ie. we missed the LR restore).

Fix it by doing the patching under stop machine. The CPUs that aren't doing the patching will be spinning in the core of the stop machine logic. That is currently sufficient for our purposes, because none of the patching we do is to that code or anywhere in the vicinity.

AI Insight

LLM-synthesized narrative grounded in this CVE's description and references.

Affected products

91

Patches

Vulnerability mechanics

References

9

News mentions

0

No linked articles in our index yet.