[PATCH 24/27] bpf: Restrict kernel image access functions when the kernel is locked down

[Matthew Garrett]

From: David Howells <dhowells at redhat.com>

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 at gmail.com>
Signed-off-by: David Howells <dhowells at redhat.com>
cc: netdev at vger.kernel.org
cc: Chun-Yi Lee <jlee at suse.com>
cc: Alexei Starovoitov <alexei.starovoitov at gmail.com>
---
 kernel/bpf/syscall.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 8577bb7f8be6..e78dbe5473c9 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2593,6 +2593,9 @@ 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;
-- 
2.21.0.352.gf09ad66450-goog