# CVE-2026-93259: powerpc/irq: Fix missing r2 clobber in PCREL inline assembly

CVE-2026-93259 is fixed in 2 products on 1 platform, first by DEBIAN-CVE-2026-93259, released September 24, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-93259
- Priority: Routine
- CVSS: 4.1 (Moderate)
- EPSS: 0.0019
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Sep 24, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-93259

## Description

In the Linux kernel, the following vulnerability has been resolved:  powerpc/irq: Fix missing r2 clobber in PCREL inline assembly  In CONFIG_PPC_KERNEL_PCREL mode, r2 is no longer reserved for the TOC pointer and is available as a caller-saved register [0].  Both call_do_irq() and call_do_softirq() use inline assembly to call functions with stack switching, but fail to list r2 in their clobber lists. This causes the compiler to assume r2 is preserved across these calls, leading to register corruption when the called functions (__do_irq and __do_softirq) clobber r2.  As a result of this kernel crash during interrupt handling is seen and the kernel fails to boot:  BUG: Unable to handle kernel data access on write at 0xc000000404697638 Faulting instruction address: 0xc0000000000181ec Oops: Kernel access of bad area, sig: 11 [#1] NIP [c0000000000181ec] __do_IRQ+0x6c/0xc0  With older GCC, the compiler would conservatively allocate callee-saved registers (like r31) for values spanning function calls, accidentally avoiding the bug:  <__do_IRQ>: 00 00 00 60 	nop a6 02 08 7c 	mflr    r0 f8 ff e1 fb 	std     r31,-8(r1) f0 ff c1 fb 	std     r30,-16(r1) 2d 03 10 06 	pla     r31,53297316  ...  3d e8 ff 4b 	bl      c0000000000165ac <__do_irq> 00 00 21 e8 	ld      r1,0(r1) 28 00 4d e9 	ld      r10,40(r13) 40 00 21 38 	addi    r1,r1,64 2a f9 aa 7f 	stdx    r29,r10,r31  With newer GCC 14, the compiler uses r2 for such values, exposing the missing clobber specification:  <__do_IRQ>: 00 00 00 60     nop a6 02 08 7c     mflr    r0 f0 ff c1 fb     std     r30,-16(r1) f8 ff e1 fb     std     r31,-8(r1) 29 02 10 06     pla     r2,36252592     # c0000000022aadc0 <__irq_regs>  ...  85 dc ff 4b 	bl      c000000000015ee0 <__do_irq> 00 00 21 e8 	ld      r1,0(r1) 28 00 2d e9 	ld      r9,40(r13) 30 00 21 38 	addi    r1,r1,48 2a 11 c9 7f 	stdx    r30,r9,r2  Fix this by adding r2 to the clobber list for both call_do_irq() and call_do_softirq() when CONFIG_PPC_KERNEL_PCREL is enabled.  [0]: https://www.mail-archive.com/gcc-patches@gcc.gnu.org/msg313226.html

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.12.111-1 | [DEBIAN-CVE-2026-93259](https://patchblox.com/security/data/fix/linux/debian-cve-2026-93259.md) | Sep 24, 2026 |
| Linux | linux Debian 14 | 7.2.6-1 | [DEBIAN-CVE-2026-93259](https://patchblox.com/security/data/fix/linux/debian-cve-2026-93259.md) | Sep 24, 2026 |
| Linux | linux-6.12 Debian 12.15 (bookworm) | 6.12.111-1~deb12u1 | [DEBIAN-CVE-2026-93259](https://patchblox.com/security/data/fix/linux/debian-cve-2026-93259.md) | Sep 24, 2026 |

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Data as of 2026-11-08T06:59:42Z 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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