# CVE-2022-49955: powerpc/rtas: Fix RTAS MSR[HV] handling for Cell

Status: published. Published: 2025-06-18. Updated: 2026-11-05.

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

powerpc/rtas: Fix RTAS MSR[HV] handling for Cell

The semi-recent changes to MSR handling when entering RTAS (firmware)
cause crashes on IBM Cell machines. An example trace:

  kernel tried to execute user page (2fff01a8) - exploit attempt? (uid: 0)
  BUG: Unable to handle kernel instruction fetch
  Faulting instruction address: 0x2fff01a8
  Oops: Kernel access of bad area, sig: 11 [#1]
  BE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=4 NUMA Cell
  Modules linked in:
  CPU: 0 PID: 0 Comm: swapper/0 Tainted: G        W          6.0.0-rc2-00433-gede0a8d3307a #207
  NIP:  000000002fff01a8 LR: 0000000000032608 CTR: 0000000000000000
  REGS: c0000000015236b0 TRAP: 0400   Tainted: G        W           (6.0.0-rc2-00433-gede0a8d3307a)
  MSR:  0000000008001002 <ME,RI>  CR: 00000000  XER: 20000000
  ...
  NIP 0x2fff01a8
  LR  0x32608
  Call Trace:
    0xc00000000143c5f8 (unreliable)
    .rtas_call+0x224/0x320
    .rtas_get_boot_time+0x70/0x150
    .read_persistent_clock64+0x114/0x140
    .read_persistent_wall_and_boot_offset+0x24/0x80
    .timekeeping_init+0x40/0x29c
    .start_kernel+0x674/0x8f0
    start_here_common+0x1c/0x50

Unlike PAPR platforms where RTAS is only used in guests, on the IBM Cell
machines Linux runs with MSR[HV] set but also uses RTAS, provided by
SLOF.

Fix it by copying the MSR[HV] bit from the MSR value we've just read
using mfmsr into the value used for RTAS.

It seems like we could also fix it using an #ifdef CELL to set MSR[HV],
but that doesn't work because it's possible to build a single kernel
image that runs on both Cell native and pseries.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- Linux / Linux: ≥ b6b1c3ce06ca438eb24e0f45bf0e63ecad0369f5; < 8b08d4f97233d8e58fff2fd9d5f86397a49733c5 (affected, git); ≥ b6b1c3ce06ca438eb24e0f45bf0e63ecad0369f5; < 91926d8b7e71aaf5f84f0cf208fc5a8b7a761050 (affected, git); 5ca40fcf0da0ce2b5bc44e7d8b036535955f2e3d (affected, git); 5f4367448f6817c8a0e94dc9736ed84fa8eee4a3 (affected, git); c9c41f0273826a13ac93124e66a4ff45df281ba0 (affected, git); ≥ 5.15.46; < 5.16 (affected, semver); ≥ 5.17.14; < 5.18 (affected, semver); ≥ 5.18.3; < 5.19 (affected, semver). Source: CNA: Linux
- Linux / Linux: 5.19 (affected); ≥ 0; < 5.19 (unaffected, semver); ≥ 5.19.8; ≤ 5.19.* (unaffected, semver); ≥ 6.0; ≤ * (unaffected, original_commit_for_fix). Source: CNA: Linux

## Severity and prioritization

- CISA KEV: No listing in collected sources

- EPSS: 0.21% as of 2026-11-05; percentile 11.14%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: Not reported

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://git.kernel.org/stable/c/8b08d4f97233d8e58fff2fd9d5f86397a49733c5 (CNA: Linux)

- https://git.kernel.org/stable/c/91926d8b7e71aaf5f84f0cf208fc5a8b7a761050 (CNA: Linux)

## Provenance

- CNA: Linux: https://www.cve.org/CVERecord?id=CVE-2022-49955; retrieved 2026-11-05; source updated 2026-11-05

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2022-49955; retrieved 2026-11-05; source updated Not reported

Revision: 62fb29b34a3edeb36e2903f53f1e689a16cece4e7ff4fa6759a7d45ee81d12fe

Canonical: https://y2.dev/cve/CVE-2022-49955

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