GHSA-XJXR-6FHH-44VQ
Vulnerability from github – Published: 2026-09-17 18:31 – Updated: 2026-09-17 18:31In 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_reg(). Unlike x86-64 and arm64, s390x does not report arena violations from its exception handler, so there is no access direction to correct here, only the missing register clear.
{
"affected": [],
"aliases": [
"CVE-2026-90211"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-17T17:17:16Z",
"severity": null
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf, s390: Clear fetch destination on faulting arena atomic\n\nSame missing register clear as on riscv64. A RMW atomic on an arena pointer\nis converted to BPF_PROBE_ATOMIC and gets an exception table entry, but\nbpf_jit_probe_atomic_pre() only fills in the arena base and the probe\noffset, leaving probe-\u003ereg at the -1 that bpf_jit_probe_init() set, which\nbpf_jit_probe_post() writes into the entry and ex_handler_bpf() then reads\nback as \"there is nothing to clear\".\n\nThat is right for a plain BPF_{ADD,AND,OR,XOR}, which only writes memory,\nbut an RMW carrying BPF_FETCH also reads the old value into a register:\nsrc_reg for BPF_{ADD,AND,OR,XOR} | BPF_FETCH and BPF_XCHG, and r0 for\nBPF_CMPXCHG. So on a fault over an unmapped arena page the program resumes\nat the landing pad with whatever that register held before the atomic\ninstead of the 0 that every other BPF_PROBE_* access delivers.\n\nFill probe-\u003ereg in from bpf_atomic_load_reg(). Unlike x86-64 and arm64,\ns390x does not report arena violations from its exception handler, so there\nis no access direction to correct here, only the missing register clear.",
"id": "GHSA-xjxr-6fhh-44vq",
"modified": "2026-09-17T18:31:55Z",
"published": "2026-09-17T18:31:55Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-90211"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/1a26541b3f60ce447433a4c4dd56edb10d2cd580"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/44b702fceb4cf3a4ddbfb496f487b034814bf1a3"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/cc3e12330599f097f0e1f792435686ddc276f26d"
}
],
"schema_version": "1.4.0",
"severity": []
}
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