CVE-2026-90195riscv, bpf: Fix missing sign-ext for signed 1-byte and 2-byte kfunc args

Official description

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.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/555fc6f1caf00ce7005e732b688da26c0dc3c5c5
• https://git.kernel.org/stable/c/801ae90f8ce099187e6224cec7d72d07a4df0324
• https://git.kernel.org/stable/c/71dbd143be598954ae103feadd12692aeb0f2f88
• https://git.kernel.org/stable/c/f2aaa621591093cfe8224a25ef2f04a3b1e304b0