CVE-2021-46928: parisc: Clear stale IIR value on instruction access rights trap

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2024-02-27 · updated 2026-06-17
Weakness: CWE-755

Description

In the Linux kernel, the following vulnerability has been resolved: parisc: Clear stale IIR value on instruction access rights trap When a trap 7 (Instruction access rights) occurs, this means the CPU couldn't execute an instruction due to missing execute permissions on the memory region. In this case it seems the CPU didn't even fetched the instruction from memory and thus did not store it in the cr19 (IIR) register before calling the trap handler. So, the trap handler will find some random old stale value in cr19. This patch simply overwrites the stale IIR value with a constant magic "bad food" value (0xbaadf00d), in the hope people don't start to try to understand the various random IIR values in trap 7 dumps.

Affected products

Linux kernel: before 5.10.90; from 5.11.0 before 5.15.13 — fixed in 5.10.90, 5.15.13

How to fix

Upgrade to a fixed version: Linux kernel 5.10.90, 5.15.13. Check the vendor advisory for mitigations.

References

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