# CVE-2021-47632: linux: In the Linux kernel, the following vulnerability has been resolved:  powerpc/set_memory: Avoid spinlock recursion in...

CVE-2021-47632 is fixed in linux on 1 platform, first by DEBIAN-CVE-2021-47632, released February 26, 2025. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2021-47632
- Priority: Routine
- CVSS: 5.5 (medium)
- EPSS: 0.0019
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Feb 26, 2025

## Description

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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 5.17.3-1 | [DEBIAN-CVE-2021-47632](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47632.md) | Feb 26, 2025 |
| Linux | linux Debian 13.5 (trixie) | 5.17.3-1 | [DEBIAN-CVE-2021-47632](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47632.md) | Feb 26, 2025 |
| Linux | linux Debian 14 | 5.17.3-1 | [DEBIAN-CVE-2021-47632](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47632.md) | Feb 26, 2025 |

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Data as of 2026-11-08T13:06:02Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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