CVE-2026-89489: openrisc: fix arbitrary kernel memory access via or1k_atomic syscall
In the Linux kernel, the following vulnerability has been resolved:
openrisc: fix arbitrary kernel memory access via or1katomic syscall
sysor1katomic() (syscall 244 in the "or1k" ABI) takes two user pointers, v1 and v2, and swaps the words they point to in hand-written assembly.
l.lwz r29,0(r4) l.lwz r27,0(r5) l.sw 0(r4),r27 l.sw 0(r5),r29
The pointers are not checked with accessok(). The four memory accesses also have no exception table entries.
A caller passes a kernel address as either pointer, and the syscall reads from and writes to it directly.
This gives an unprivileged process a kernel read/write primitive. It overwrites kernel data such as the syscalltable, gaining code execution in kernel context.
Check both pointers before entering the critical section. Add fixups for the four memory accesses so faults on valid but unmapped user addresses return -EFAULT.
[shorne@gmail.com: fix comment style]
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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ubuntu/linux-riscvto a version that resolves this vulnerability.Fixed in 7.0.0-42.42.1 - Compensating control
In sys_or1k_atomic() (syscall 244 in the or1k ABI), check both user pointers with access_ok() before entering the critical section, and add exception-table fixups for all four memory accesses so faults on valid but unmapped user addresses return -EFAULT.
Event History
Frequently Asked Questions
Which systems are exposed to this issue?
Systems running the Linux kernel on the OpenRISC architecture using the "or1k" ABI are exposed if they include the vulnerable or1k_atomic syscall implementation. The issue is reachable by an unprivileged local process.
What does an attacker need to exploit it?
An attacker needs the ability to execute a local unprivileged process and invoke syscall 244, sys_or1k_atomic(). They can supply a kernel address as either syscall pointer argument to read from or write to kernel memory.
Is exploitation limited to a crash or denial of service?
No. The vulnerable syscall provides a kernel read/write primitive, and the description states that an attacker can overwrite kernel data such as sys_call_table to gain code execution in kernel context.
What behavior indicates that the fix is present?
The corrected implementation checks both user pointers with access_ok() before the critical section. It also includes exception-table fixups so accesses to valid but unmapped user addresses return -EFAULT rather than faulting without recovery.