This patch extends the BPF_PROG_LOAD command by adding three new fields
to `union bpf_attr` in the user-space API:

  - signature: A pointer to the signature blob.
  - signature_size: The size of the signature blob.
  - keyring_id: The serial number of a loaded kernel keyring (e.g.,
    the user or session keyring) containing the trusted public keys.

When a BPF program is loaded with a signature, the kernel:

1.  Retrieves the trusted keyring using the provided `keyring_id`.
2.  Verifies the supplied signature against the BPF program's
    instruction buffer.
3.  If the signature is valid and was generated by a key in the trusted
    keyring, the program load proceeds.
4.  If no signature is provided, the load proceeds as before, allowing
    for backward compatibility. LSMs can chose to restrict unsigned
    programs and implement a security policy.
5.  If signature verification fails for any reason,
    the program is not loaded.

Signed-off-by: KP Singh <kpsingh@kernel.org>
---
 include/linux/bpf.h            |  9 +++++++-
 include/uapi/linux/bpf.h       | 10 +++++++++
 kernel/bpf/syscall.c           | 39 +++++++++++++++++++++++++++++++++-
 kernel/trace/bpf_trace.c       |  6 ++++--
 tools/include/uapi/linux/bpf.h | 10 +++++++++
 tools/lib/bpf/bpf.c            |  2 +-
 6 files changed, 71 insertions(+), 5 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 35f1a633d87a..32a41803d61c 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h

@@ -2778,7 +2778,14 @@ bpf_jit_find_kfunc_model(const struct bpf_prog *prog,
 int bpf_get_kfunc_addr(const struct bpf_prog *prog, u32 func_id,
                       u16 btf_fd_idx, u8 **func_addr);

-struct bpf_core_ctx {
+__bpf_kfunc struct bpf_key *bpf_lookup_user_key(u32 serial, u64 flags);