CVE-2026-90195

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

riscv, bpf: Fix missing sign-ext for signed 1-byte and 2-byte kfunc args

On RV64, the ABI requires sign-extension for signed 1-byte and 2-byte kfunc

args. However, the RV64 JIT currently does not perform sign-extension for

such kfunc args.

Before commit 7ce090afbf72 ("bpf: Infer zext_dst based on static register

liveness analysis"), state pruning could potentially omit zero-extension

of 32-bit subregisters, which inadvertently masked the above issue by making

the args appear as if they had been properly sign-extended. After that

commit, the problem is exposed, causing the kfunc_call/kfunc_call_test4

selftest to fail.

Fix this by extending the existing sign-extension logic to handle signed

1-byte and 2-byte kfunc args as well.