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From:   Yi He <clangllvm@126.com>
To:     yhs@meta.com
Cc:     andrii@kernel.org, ast@kernel.org, bpf@vger.kernel.org,
        clangllvm@126.com, daniel@iogearbox.net, haoluo@google.com,
        john.fastabend@gmail.com, jolsa@kernel.org, kpsingh@kernel.org,
        linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org,
        martin.lau@linux.dev, mhiramat@kernel.org, rostedt@goodmis.org,
        sdf@google.com, song@kernel.org, yhs@fb.com
Subject: [PATCH V2] bpf: security enhancement by limiting the offensive eBPF helpers
Date:   Wed, 18 Jan 2023 08:54:32 +0800
Message-Id: <20230118005432.634229-1-clangllvm@126.com>
In-Reply-To: <f539bfef-c098-5ff0-51ef-bfa8fd0c4661@meta.com>
References: <f539bfef-c098-5ff0-51ef-bfa8fd0c4661@meta.com>
MIME-Version: 1.0
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The bpf_send_singal, bpf_send_singal_thread and bpf_override_return
is similar to bpf_write_user and can affect userspace processes.
Thus, these three helpers should also be restricted by security lockdown.

Signed-off-by: Yi He <clangllvm@126.com>
---
 V1 -> V2: add security lockdown to bpf_send_singal_thread and remove 
	the unused LOCKDOWN_OFFENSIVE_BPF_MAX.

 include/linux/security.h | 2 ++
 kernel/trace/bpf_trace.c | 9 ++++++---
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/include/linux/security.h b/include/linux/security.h
index 5b67f208f..42420e620 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -123,6 +123,8 @@ enum lockdown_reason {
 	LOCKDOWN_DEBUGFS,
 	LOCKDOWN_XMON_WR,
 	LOCKDOWN_BPF_WRITE_USER,
+	LOCKDOWN_BPF_SEND_SIGNAL,
+	LOCKDOWN_BPF_OVERRIDE_RETURN,
 	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..fdb94868d 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1463,9 +1463,11 @@ 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;
+		return security_locked_down(LOCKDOWN_BPF_SEND_SIGNAL) < 0 ?
+		       NULL : &bpf_send_signal_thread_proto;
 	case BPF_FUNC_perf_event_read_value:
 		return &bpf_perf_event_read_value_proto;
 	case BPF_FUNC_get_ns_current_pid_tgid:
@@ -1531,7 +1533,8 @@ 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