There are some bpf functions can be used to read kernel memory:
bpf_probe_read, bpf_probe_write_user and bpf_trace_printk.  These allow
private keys in kernel memory (e.g. the hibernation image signing key) to
be read by an eBPF program and kernel memory to be altered without
restriction. Disable them if the kernel has been locked down in
confidentiality mode.

Suggested-by: Alexei Starovoitov <redacted>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Matthew Garrett <redacted>
cc: netdev@vger.kernel.org
cc: Chun-Yi Lee <jlee@suse.com>
cc: Alexei Starovoitov <redacted>
Cc: Daniel Borkmann <daniel@iogearbox.net>
---
 kernel/trace/bpf_trace.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 8b068adb9da1..9e8eda605b5e 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c

@@ -137,6 +137,9 @@ BPF_CALL_3(bpf_probe_read, void *, dst, u32, size, const void *, unsafe_ptr)
 {
        int ret;

+       if (kernel_is_locked_down("BPF", LOCKDOWN_CONFIDENTIALITY))
+               return -EINVAL;
+
        ret = probe_kernel_read(dst, unsafe_ptr, size);
        if (unlikely(ret < 0))
                memset(dst, 0, size);