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Fencer Vulns
medium 5.5

CVE-2021-47632 json

powerpc/set_memory: Avoid spinlock recursion in change_page_attr()

published 2025-02-26 20 mo ago modified 2026-06-17 4 mo ago also EUVD-2021-34672

cvss
5.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 8%
public exploits
0
none known

Summary

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

powerpc/set_memory: Avoid spinlock recursion in change_page_attr()

Commit 1f9ad21c3b38 ("powerpc/mm: Implement set_memory() routines") included a spin_lock() to change_page_attr() in order to safely perform the three step operations. But then commit 9f7853d7609d ("powerpc/mm: Fix set_memory_*() against concurrent accesses") modify it to use pte_update() and do the operation safely against concurrent access.

In the meantime, Maxime reported some spinlock recursion.

[ 15.351649] BUG: spinlock recursion on CPU#0, kworker/0:2/217 [ 15.357540] lock: init_mm+0x3c/0x420, .magic: dead4ead, .owner: kworker/0:2/217, .owner_cpu: 0 [ 15.366563] CPU: 0 PID: 217 Comm: kworker/0:2 Not tainted 5.15.0+ #523 [ 15.373350] Workqueue: events do_free_init [ 15.377615] Call Trace: [ 15.380232] [e4105ac0] [800946a4] do_raw_spin_lock+0xf8/0x120 (unreliable) [ 15.387340] [e4105ae0] [8001f4ec] change_page_attr+0x40/0x1d4 [ 15.393413] [e4105b10] [801424e0] __apply_to_page_range+0x164/0x310 [ 15.400009] [e4105b60] [80169620] free_pcp_prepare+0x1e4/0x4a0 [ 15.406045] [e4105ba0] [8016c5a0] free_unref_page+0x40/0x2b8 [ 15.411979] [e4105be0] [8018724c] kasan_depopulate_vmalloc_pte+0x6c/0x94 [ 15.418989] [e4105c00] [801424e0] __apply_to_page_range+0x164/0x310 [ 15.425451] [e4105c50] [80187834] kasan_release_vmalloc+0xbc/0x134 [ 15.431898] [e4105c70] [8015f7a8] __purge_vmap_area_lazy+0x4e4/0xdd8 [ 15.438560] [e4105d30] [80160d10] _vm_unmap_aliases.part.0+0x17c/0x24c [ 15.445283] [e4105d60] [801642d0] __vunmap+0x2f0/0x5c8 [ 15.450684] [e4105db0] [800e32d0] do_free_init+0x68/0x94 [ 15.456181] [e4105dd0] [8005d094] process_one_work+0x4bc/0x7b8 [ 15.462283] [e4105e90] [8005d614] worker_thread+0x284/0x6e8 [ 15.468227] [e4105f00] [8006aaec] kthread+0x1f0/0x210 [ 15.473489] [e4105f40] [80017148] ret_from_kernel_thread+0x14/0x1c

Remove the read / modify / write sequence to make the operation atomic and remove the spin_lock() in change_page_attr().

To do the operation atomically, we can't use pte modification helpers anymore. Because all platforms have different combination of bits, it is not easy to use those bits directly. But all have the _PAGE_KERNEL_{RO/ROX/RW/RWX} set of flags. All we need it to compare two sets to know which bits are set or cleared.

For instance, by comparing _PAGE_KERNEL_ROX and _PAGE_KERNEL_RO you know which bit gets cleared and which bit get set when changing exec permission.

Patch / fix

  • Linux Linux 5.15.34, 5.16.20, 5.17.3, 5.18
  • linux Debian 14, Debian 13, Debian 12 5.17.3-1

debian advisories DEBIAN-CVE-2021-47632

  • linux Ubuntu 22.04 LTS 5.15.0-37.39
  • linux-aws Ubuntu 22.04 LTS 5.15.0-1011.14
  • linux-gcp Ubuntu 22.04 LTS 5.15.0-1008.12
  • linux-gke Ubuntu 22.04 LTS 5.15.0-1008.10
  • linux-ibm Ubuntu 22.04 LTS 5.15.0-1007.8
  • linux-kvm Ubuntu 22.04 LTS 5.15.0-1010.11
  • linux-azure Ubuntu 22.04 LTS 5.15.0-1010.12
  • linux-raspi Ubuntu 22.04 LTS 5.15.0-1011.13

ubuntu advisories UBUNTU-CVE-2021-47632

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • kernel-64kb SLES 15 SP5-LTSS, SLE High Performance Computing 15 SP5-LTSS, SLE High Performance Computing 15 SP5-ESPOS 5.14.21-150500.55.100.1
  • kernel-syms SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE High Performance Computing 15 SP5-LTSS +1 more 5.14.21-150500.55.100.1
  • kernel-source SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE Micro 5.5 +2 more 5.14.21-150500.55.100.1
  • kernel-default SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE Micro 5.5 +3 more 5.14.21-150500.55.100.1
  • kernel-obs-build SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE High Performance Computing 15 SP5-LTSS +1 more 5.14.21-150500.55.100.1
  • kernel-default-base SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE Micro 5.5 +2 more 5.14.21-150500.55.100.1.150500.6.47.1
  • kernel-rt SLE Micro 5.4, SLE Micro 5.3 5.14.21-150400.15.115.1
  • kernel-source-rt SLE Micro 5.4, SLE Micro 5.3 5.14.21-150400.15.115.1

suse advisories SUSE-SU-2025:1241-1SUSE-SU-2025:1183-1SUSE-SU-2025:1176-1SUSE-SU-2025:1027-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-47632 updated cvss 5.5

kernel: powerpc/set_memory: Avoid spinlock recursion in change_page_attr()

  • Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more
    affected: no fix available “Fix deferred”
  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more Red Hat Enterprise Linux 10 kernel
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
13 mo ago

Exploit prediction

0.19% chance of exploitation in the next 30 days, higher than 8% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CISA ADP 3.1 5.5 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
NVD 3.1 5.5 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
CNA 3.1 5.5 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected products

  • Linux Linux

Classification

Weakness
Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.