CVE-2026-90211

/// Technical description

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

bpf, s390: Clear fetch destination on faulting arena atomic

Same missing register clear as on riscv64. A RMW atomic on an arena pointer

is converted to BPF_PROBE_ATOMIC and gets an exception table entry, but

bpf_jit_probe_atomic_pre() only fills in the arena base and the probe

offset, leaving probe->reg at the -1 that bpf_jit_probe_init() set, which

bpf_jit_probe_post() writes into the entry and ex_handler_bpf() then reads

back as "there is nothing to clear".

That is right for a plain BPF_{ADD,AND,OR,XOR}, which only writes memory,

but an RMW carrying BPF_FETCH also reads the old value into a register:

src_reg for BPF_{ADD,AND,OR,XOR} | BPF_FETCH and BPF_XCHG, and r0 for

BPF_CMPXCHG. So on a fault over an unmapped arena page the program resumes

at the landing pad with whatever that register held before the atomic

instead of the 0 that every other BPF_PROBE_* access delivers.

Fill probe->reg in from bpf_atomic_load_

/// 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