CVE-2023-52499 powerpc/47x: Fix 47x syscall return crash

Medium 5.5 Published 2 Mar 2024 Updated 11 May 2026

A flaw in the Linux kernel's PowerPC 47x syscall return logic causes a crash or potential code execution due to incorrect register usage during instruction cache flushes.

Exploited in the wild: Not known
Login needed: Any signed-in user
Attackable: Local or same network only
Victim action needed: Not needed
Fix: Available

What is CVE-2023-52499?

CVE-2023-52499 is a medium-severity memory corruption vulnerability in Linux kernel, published on 2 Mar 2024. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

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

powerpc/47x: Fix 47x syscall return crash

Eddie reported that newer kernels were crashing during boot on his 476 FSP2 system:

kernel tried to execute user page (b7ee2000) - exploit attempt? (uid: 0) BUG: Unable to handle kernel instruction fetch Faulting instruction address: 0xb7ee2000 Oops: Kernel access of bad area, sig: 11 [#1] BE PAGE_SIZE=4K FSP-2 Modules linked in: CPU: 0 PID: 61 Comm: mount Not tainted 6.1.55-d23900f.ppcnf-fsp2 #1 Hardware name: ibm,fsp2 476fpe 0x7ff520c0 FSP-2 NIP: b7ee2000 LR: 8c008000 CTR: 00000000 REGS: bffebd83 TRAP: 0400 Not tainted (6.1.55-d23900f.ppcnf-fs p2) MSR: 00000030 <IR,DR> CR: 00001000 XER: 20000000 GPR00: c00110ac bffebe63 bffebe7e bffebe88 8c008000 00001000 00000d12 b7ee2000 GPR08: 00000033 00000000 00000000 c139df10 48224824 1016c314 10160000 00000000 GPR16: 10160000 10160000 00000008 00000000 10160000 00000000 10160000 1017f5b0 GPR24: 1017fa50 1017f4f0 1017fa50 1017f740 1017f630 00000000 00000000 1017f4f0 NIP [b7ee2000] 0xb7ee2000 LR [8c008000] 0x8c008000 Call Trace: Instruction dump: XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX ---[ end trace 0000000000000000 ]---

The problem is in ret_from_syscall where the check for icache_44x_need_flush is done. When the flush is needed the code jumps out-of-line to do the flush, and then intends to jump back to continue the syscall return.

However the branch back to label 1b doesn't return to the correct location, instead branching back just prior to the return to userspace, causing bogus register values to be used by the rfi.

The breakage was introduced by commit 6f76a01173cc ("powerpc/syscall: implement system call entry/exit logic in C for PPC32") which inadvertently removed the "1" label and reused it elsewhere.

Fix it by adding named local labels in the correct locations. Note that the return label needs to be outside the ifdef so that CONFIG_PPC_47x=n compiles.

Which versions are affected by CVE-2023-52499?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2023-52499?

Apply the vendor's patch.

Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.

Is CVE-2023-52499 being exploited?

There is no known exploitation of CVE-2023-52499 in the wild and no public exploit code.

All Linux kernel vulnerabilities

Sources

Also known as BELL-CVE-2023-52499, DEBIAN-CVE-2023-52499, GHSA-8w3f-mchr-v6jh, UBUNTU-CVE-2023-52499.