On Wed, May 28, 2025 at 02:49:03PM -0700, Blaise Boscaccy wrote:
> + if (!attr->signature_maps_size) {
> + sha256((u8 *)prog->insnsi, prog->len * sizeof(struct bpf_insn), (u8 *)&hash);
> + err = verify_pkcs7_signature(hash, sizeof(hash), signature, attr->signature_size,
> + VERIFY_USE_SECONDARY_KEYRING,
> + VERIFYING_EBPF_SIGNATURE,
> + NULL, NULL);
Has this ever been tested?
It looks like it will always return -EINVAL because:
verify_pkcs7_signature()
verify_pkcs7_message_sig()
pkcs7_verify()
... pkcs7_verify() contains a switch statement which you're not
amending with a "case VERIFYING_EBPF_SIGNATURE" but which returns
-EINVAL in the "default" case.
Aside from that, you may want to consider introducing a new ".ebpf"
keyring to allow adding trusted keys specifically for eBPF verification
without having to rely on the system keyring.
Constraining oneself to sha256 doesn't seem future-proof.
Some minor style issues in the commit message caught my eye:
> This introduces signature verification for eBPF programs inside of the
> bpf subsystem. Two signature validation schemes are included, one that
Use imperative mood, avoid repetitive "This ...", e.g.
"Introduce signature verification of eBPF programs..."
> The signature check is performed before the call to
> security_bpf_prog_load. This allows the LSM subsystem to be clued into
> the result of the signature check, whilst granting knowledge of the
> method and apparatus which was employed.
"Perform the signature check before calling security_bpf_prog_load()
to allow..."
Thanks,
Lukas
