VYPR
← All advisories
Unrated severityNVD Advisory· Published Feb 28, 2024· Updated May 4, 2025

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

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.

Affected products

90

Patches

0

No patches discovered yet.

Vulnerability mechanics

AI mechanics synthesis has not run for this CVE yet.

References

9

News mentions

0

No linked articles in our index yet.