[PATCH] bpf: security enhancement by limiting the offensive eBPF helpers

[WritePaper]

The bpf_send_singal and bpf_override_return is similar to
bpf_write_user and can affect userspace processes. Thus, these two
helpers should also be constraint by security lockdown.

Signed-off-by: WritePaper <clangllvm@xxxxxxx>
---
 include/linux/security.h | 3 +++
 kernel/trace/bpf_trace.c | 6 ++++--
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/include/linux/security.h b/include/linux/security.h
index 5b67f208f..cb90b2860 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -123,6 +123,9 @@ enum lockdown_reason {
 	LOCKDOWN_DEBUGFS,
 	LOCKDOWN_XMON_WR,
 	LOCKDOWN_BPF_WRITE_USER,
+	LOCKDOWN_BPF_SEND_SIGNAL,
+	LOCKDOWN_BPF_OVERRIDE_RETURN,
+	LOCKDOWN_OFFENSIVE_BPF_MAX,
 	LOCKDOWN_DBG_WRITE_KERNEL,
 	LOCKDOWN_RTAS_ERROR_INJECTION,
 	LOCKDOWN_INTEGRITY_MAX,
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 3bbd3f0c8..3a80f4b6f 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1463,7 +1463,8 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_cgrp_storage_delete_proto;
 #endif
 	case BPF_FUNC_send_signal:
-		return &bpf_send_signal_proto;
+		return security_locked_down(LOCKDOWN_BPF_SEND_SIGNAL) < 0 ?
+		       NULL : &bpf_send_signal_proto;
 	case BPF_FUNC_send_signal_thread:
 		return &bpf_send_signal_thread_proto;
 	case BPF_FUNC_perf_event_read_value:
@@ -1531,7 +1532,8 @@ kprobe_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_get_stack_proto;
 #ifdef CONFIG_BPF_KPROBE_OVERRIDE
 	case BPF_FUNC_override_return:
-		return &bpf_override_return_proto;
+		return security_locked_down(LOCKDOWN_BPF_OVERRIDE_RETURN) < 0 ?
+		       NULL : &bpf_override_return_proto;
 #endif
 	case BPF_FUNC_get_func_ip:
 		return prog->expected_attach_type == BPF_TRACE_KPROBE_MULTI ?
-- 
2.25.1