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 0027-bpf-Restrict-kernel-image-access-functions-when-the-.patch

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 5cb783fc8224b3c5acb65bae4d79c0ec74a71c7a..673ac3714edfe2d799e375aef0028e72cc1aa535 100644 (file)
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -1690,6 +1690,9 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz
        if (!capable(CAP_SYS_ADMIN) && sysctl_unprivileged_bpf_disabled)
                return -EPERM;
 
+       if (kernel_is_locked_down("BPF"))
+               return -EPERM;
+
        err = check_uarg_tail_zero(uattr, sizeof(attr), size);
        if (err)
                return err;