[PATCH V31 22/25] bpf: Restrict bpf when kernel lockdown is in confidentiality mode

[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. Disable them if the kernel has been locked down in
confidentiality mode.

Suggested-by: Alexei Starovoitov <alexei.starovoitov at gmail.com>
Signed-off-by: David Howells <dhowells at redhat.com>
Signed-off-by: Matthew Garrett <mjg59 at google.com>
cc: netdev at vger.kernel.org
cc: Chun-Yi Lee <jlee at suse.com>
cc: Alexei Starovoitov <alexei.starovoitov at gmail.com>
Cc: Daniel Borkmann <daniel at 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);
@@ -156,6 +159,8 @@ static const struct bpf_func_proto bpf_probe_read_proto = {
 BPF_CALL_3(bpf_probe_write_user, void *, unsafe_ptr, const void *, src,
 	   u32, size)
 {
+	if (kernel_is_locked_down("BPF", LOCKDOWN_CONFIDENTIALITY))
+		return -EINVAL;
 	/*
 	 * Ensure we're in user context which is safe for the helper to
 	 * run. This helper has no business in a kthread.
@@ -207,6 +212,9 @@ BPF_CALL_5(bpf_trace_printk, char *, fmt, u32, fmt_size, u64, arg1,
 	char buf[64];
 	int i;
 
+	if (kernel_is_locked_down("BPF", LOCKDOWN_CONFIDENTIALITY))
+		return -EINVAL;
+
 	/*
 	 * bpf_check()->check_func_arg()->check_stack_boundary()
 	 * guarantees that fmt points to bpf program stack,
@@ -535,6 +543,9 @@ BPF_CALL_3(bpf_probe_read_str, void *, dst, u32, size,
 {
 	int ret;
 
+	if (kernel_is_locked_down("BPF", LOCKDOWN_CONFIDENTIALITY))
+		return -EINVAL;
+
 	/*
 	 * The strncpy_from_unsafe() call will likely not fill the entire
 	 * buffer, but that's okay in this circumstance as we're probing
-- 
2.21.0.392.gf8f6787159e-goog