linux-kernel - [PATCH V33 24/30] bpf: Restrict bpf when kernel lockdown is in confidentiality mode

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Date:   Thu, 20 Jun 2019 18:19:35 -0700
From:   Matthew Garrett <matthewgarrett@...gle.com>
To:     jmorris@...ei.org
Cc:     linux-security@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-api@...r.kernel.org, David Howells <dhowells@...hat.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Matthew Garrett <mjg59@...gle.com>, netdev@...r.kernel.org,
        Chun-Yi Lee <jlee@...e.com>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: [PATCH V33 24/30] bpf: Restrict bpf when kernel lockdown is in
 confidentiality mode

From: David Howells <dhowells@...hat.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@...il.com>
Signed-off-by: David Howells <dhowells@...hat.com>
Signed-off-by: Matthew Garrett <mjg59@...gle.com>
cc: netdev@...r.kernel.org
cc: Chun-Yi Lee <jlee@...e.com>
cc: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Daniel Borkmann <daniel@...earbox.net>
---
 include/linux/security.h     |  1 +
 kernel/trace/bpf_trace.c     | 11 +++++++++++
 security/lockdown/lockdown.c |  1 +
 3 files changed, 13 insertions(+)

diff --git a/include/linux/security.h b/include/linux/security.h
index dae4aa83352c..8bf426cdd151 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -97,6 +97,7 @@ enum lockdown_reason {
 	LOCKDOWN_INTEGRITY_MAX,
 	LOCKDOWN_KCORE,
 	LOCKDOWN_KPROBES,
+	LOCKDOWN_BPF,
 	LOCKDOWN_CONFIDENTIALITY_MAX,
 };
 
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index d64c00afceb5..6f57485df840 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 (security_is_locked_down(LOCKDOWN_BPF))
+		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 (security_is_locked_down(LOCKDOWN_BPF))
+		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 (security_is_locked_down(LOCKDOWN_BPF))
+		return -EINVAL;
+
 	/*
 	 * bpf_check()->check_func_arg()->check_stack_boundary()
 	 * guarantees that fmt points to bpf program stack,
@@ -534,6 +542,9 @@ BPF_CALL_3(bpf_probe_read_str, void *, dst, u32, size,
 {
 	int ret;
 
+	if (security_is_locked_down(LOCKDOWN_BPF))
+		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
diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
index 89ad853daec2..0a3bbf1ba01d 100644
--- a/security/lockdown/lockdown.c
+++ b/security/lockdown/lockdown.c
@@ -33,6 +33,7 @@ static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
 	[LOCKDOWN_INTEGRITY_MAX] = "integrity",
 	[LOCKDOWN_KCORE] = "/proc/kcore access",
 	[LOCKDOWN_KPROBES] = "use of kprobes",
+	[LOCKDOWN_BPF] = "use of bpf",
 	[LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
 };
 
-- 
2.22.0.410.gd8fdbe21b5-goog