CVE-2026-98049

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

bpf: zero extend the result of an arena 32-bit cmpxchg

bpf convert ctx accesses() rewrites an atomic on an arena pointer from BPF STX | BPF ATOMIC to BPF STX | BPF PROBE ATOMIC, and it runs before bpf opt subreg zext lo32 rnd hi32().

That pass emits an explicit zero extension for a 32-bit cmpxchg even when bpf jit needs zext() is false. This is done because on some architectures 32-bit cmpxchg requires explicit zero extension for the dst register. E.g. on x86-64 'lock cmpxchg' does not change the %eax if comparison is successful, while BPF semantics declare that each operation on a 32-bit register zero extends it's upper half.

is cmpxchg insn() matches BPF MODE == BPF ATOMIC only, so an arena cmpxchg misses said zero extension adjustment. This patch adjusts is cmpxchg insn() to match BPF PROBE ATOMIC alongside BPF ATOMIC.