CVE-2026-93167

/// Technical description

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

csky: Fix a4/a5 restoration in syscall trace path

The syscall trace path reloads syscall arguments from pt_regs before

calling the syscall handler. On C-SKY ABIv2, the 5th and 6th syscall

arguments are prepared as stack arguments before invoking syscallid.

The current code adjusts sp before loading LSAVE_A4 and LSAVE_A5. Since

those offsets are relative to the original pt_regs base, loading them

after changing sp fetches the wrong slots. As a result, traced syscalls

that use the 5th or 6th argument may receive corrupted arguments.

This is visible with mmap2(), which takes six arguments. A small

PTRACE_SYSCALL reproducer opens a file and maps one page with:

mmap(NULL, 4096, PROT_READ | PROT_EXEC, MAP_PRIVATE, fd, 0)

Before the fix, the traced child fails the mmap and exits with 12.

After the fix, the mapping succeeds and the child exits with 0.

Fix the trace path by loading a4/a5 from pt_regs before changing sp

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References