bpf: Restrict kernel image access functions when the kernel is locked down

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.

Completely prohibit the use of BPF when the kernel is locked down.

Suggested-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: netdev@vger.kernel.org
cc: Chun-Yi Lee <jlee@suse.com>
cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>

Gbp-Pq: Topic features/all/lockdown
Gbp-Pq: Name 0025-bpf-Restrict-kernel-image-access-functions-when-the-.patch

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 42d17f7307802a0c2196e59ee5d5abcb37184258..19633a810f5ebaa965a2c8297f738bf78860cf77 100644 (file)
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2777,6 +2777,9 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz
        if (sysctl_unprivileged_bpf_disabled && !capable(CAP_SYS_ADMIN))
                return -EPERM;
 
+       if (kernel_is_locked_down("BPF"))
+               return -EPERM;
+
        err = bpf_check_uarg_tail_zero(uattr, sizeof(attr), size);
        if (err)
                return err;