Linux Kernel Unaligned Access Vulnerability in PARISC Architecture Stack Unwinding

A vulnerability in the Linux kernel's stack unwinding process for the PARISC architecture can lead to a system crash. This issue arises from unaligned memory access, which triggers a trap handler for unalignment, causing a spinlock recursion that ultimately results in a deadlock. The problem was reported by Guenter Roeck on an emulated B160L machine, where the network management tool 'udhcpc' was running. The crash occurred during the stack unwinding process, as the unwinder attempted to read from unaligned memory without proper alignment checks, leading to a failure in the memory access and a subsequent system hang.

Impact

Exploitation of this vulnerability causes a kernel crash, leading to a deadlock situation where the system becomes unresponsive. This occurs due to a spinlock recursion triggered by the unaligned memory access, which interrupts normal process scheduling and handling.

Reproduction

The vulnerability can be reproduced on a PARISC architecture machine, particularly in an emulated environment using the B160L machine model. The 'udhcpc' network management tool can be used to trigger the issue. During the execution of 'udhcpc', the kernel's stack unwinding process will encounter unaligned memory accesses, leading to a crash and a deadlock situation.

Remediation

Users can upgrade to the latest version of the Linux kernel where this vulnerability has been addressed. The specific commit that resolves this issue is available in the Linux kernel stable tree.