bpf: Restrict bpf when kernel lockdown is in confidentiality mode

bpf: Restrict bpf when kernel lockdown is in confidentiality mode

bpf_read() and bpf_read_str() could potentially be abused to (eg) allow
private keys in kernel memory to be leaked. Disable them if the kernel
has been locked down in confidentiality mode.

Suggested-by: Alexei Starovoitov <[email protected]>
Signed-off-by: Matthew Garrett <[email protected]>
Reviewed-by: Kees Cook <[email protected]>
cc: [email protected]
cc: Chun-Yi Lee <[email protected]>
cc: Alexei Starovoitov <[email protected]>
Cc: Daniel Borkmann <[email protected]>
Signed-off-by: James Morris <[email protected]>