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Date: Tue, 5 Jan 2021 16:00:27 +0800
From: Xichen Lin <linxichen.01@...edance.com>
To: ast@...nel.org, daniel@...earbox.net, andrii@...nel.org
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
bpf@...r.kernel.org, netdev@...r.kernel.org,
wangdongdong.6@...edance.com, cong.wang@...edance.com,
Xichen Lin <linxichen.01@...edance.com>
Subject: [PATCH] bpf: Add signature checking for BPF programs
From: Xichen Lin <linxichen.01@...edance.com>
Check the signature of a BPF program against the same set of keys for
module signature checking.
Currently the format of a signed BPF program is similar to that of
a signed kernel module, composed of BPF bytecode, signature,
module_signature structure and a magic string, in order, aligned to
struct sock_filter.
Signed-off-by: Xichen Lin <linxichen.01@...edance.com>
---
include/linux/bpf_sig.h | 26 ++++++++++++++++++
init/Kconfig | 10 +++++++
kernel/bpf/Makefile | 3 +++
kernel/bpf/bpf_sig.c | 70 +++++++++++++++++++++++++++++++++++++++++++++++++
kernel/bpf/syscall.c | 5 ++++
kernel/sysctl.c | 14 ++++++++++
6 files changed, 128 insertions(+)
create mode 100644 include/linux/bpf_sig.h
create mode 100644 kernel/bpf/bpf_sig.c
diff --git a/include/linux/bpf_sig.h b/include/linux/bpf_sig.h
new file mode 100644
index 000000000000..da87ba50f340
--- /dev/null
+++ b/include/linux/bpf_sig.h
@@ -0,0 +1,26 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * Copyright (C) 2020 Bytedance
+ */
+
+#ifndef _LINUX_BPF_SIG_H
+#define _LINUX_BPF_SIG_H
+
+#include <linux/bpf.h>
+
+#define BPF_PROG_SIG_STRING "~BPF signature appended~\n"
+
+#ifdef CONFIG_BPF_SIGNATURE
+extern int sysctl_bpf_signature_enable;
+#endif /* CONFIG_BPF_SIGNATURE */
+
+#ifdef CONFIG_BPF_SIGNATURE
+int bpf_check_prog_sig(struct bpf_prog *prog);
+#else
+static inline int bpf_check_prog_sig(struct bpf_prog *prog)
+{
+ return 0;
+}
+#endif /* CONFIG_BPF_SIGNATURE */
+#endif /* _LINUX_BPF_SIG_H */
diff --git a/init/Kconfig b/init/Kconfig
index b77c60f8b963..24225c966803 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -2212,6 +2212,16 @@ config MODULE_SIG_HASH
default "sha384" if MODULE_SIG_SHA384
default "sha512" if MODULE_SIG_SHA512
+config BPF_SIGNATURE
+ bool "BPF program signature verification"
+ depends on MODULE_SIG
+ help
+ Check BPF programs for valid signatures upon load: the signature
+ is appended to the end of the BPF program similar to module signing.
+
+ BPF signature checking will use the same kernel facilities as
+ module signature checking as well as the keys and hash functions.
+
config MODULE_COMPRESS
bool "Compress modules on installation"
help
diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
index d1249340fd6b..c6d2b200e795 100644
--- a/kernel/bpf/Makefile
+++ b/kernel/bpf/Makefile
@@ -37,3 +37,6 @@ obj-$(CONFIG_BPF_SYSCALL) += bpf_struct_ops.o
obj-${CONFIG_BPF_LSM} += bpf_lsm.o
endif
obj-$(CONFIG_BPF_PRELOAD) += preload/
+ifeq ($(CONFIG_BPF_SIGNATURE),y)
+obj-$(CONFIG_BPF_SIGNATURE) += bpf_sig.o
+endif
diff --git a/kernel/bpf/bpf_sig.c b/kernel/bpf/bpf_sig.c
new file mode 100644
index 000000000000..7fcfc1b5d5d8
--- /dev/null
+++ b/kernel/bpf/bpf_sig.c
@@ -0,0 +1,70 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2021 Bytedance */
+
+#include <linux/bpf.h>
+#include <linux/filter.h>
+#include <linux/bpf_sig.h>
+#include <linux/module_signature.h>
+#include <linux/verification.h>
+
+int sysctl_bpf_signature_enable;
+
+static bool bpf_strip_prog_ms(struct bpf_prog *prog, unsigned int *sig_len_ptr)
+{
+ void *data = (void *) prog->insns;
+ unsigned int prog_len = bpf_prog_size(prog->len) - sizeof(struct bpf_prog);
+ unsigned int rounded_ms_len = round_up(sizeof(struct module_signature),
+ sizeof(struct sock_filter));
+ struct module_signature *ms = (struct module_signature *)
+ (data + prog_len - rounded_ms_len);
+ unsigned int rounded_sig_len;
+
+ *sig_len_ptr = be32_to_cpu(ms->sig_len);
+ rounded_sig_len = round_up(*sig_len_ptr, sizeof(struct sock_filter));
+
+ if (mod_check_sig(ms, prog_len, "bpf"))
+ return false;
+
+ if (prog_len > rounded_ms_len + rounded_sig_len) {
+ prog->len -= rounded_ms_len / sizeof(struct sock_filter);
+ prog->len -= rounded_sig_len / sizeof(struct sock_filter);
+ return true;
+ }
+
+ return false;
+}
+
+static bool bpf_strip_prog_sig(struct bpf_prog *prog, unsigned int *sig_len_ptr)
+{
+ void *data = (void *) prog->insns;
+ const unsigned int marker_len = sizeof(BPF_PROG_SIG_STRING) - 1;
+ const unsigned int rounded_marker_len = round_up(marker_len,
+ sizeof(struct sock_filter));
+ unsigned int prog_len = bpf_prog_size(prog->len) - sizeof(struct bpf_prog);
+
+ if (prog_len > rounded_marker_len &&
+ memcmp(data + prog_len - rounded_marker_len,
+ BPF_PROG_SIG_STRING, marker_len) == 0) {
+ prog->len -= rounded_marker_len / sizeof(struct sock_filter);
+ return bpf_strip_prog_ms(prog, sig_len_ptr);
+ }
+
+ return false;
+}
+
+int bpf_check_prog_sig(struct bpf_prog *prog)
+{
+ bool stripped;
+ unsigned int sig_len;
+
+ stripped = bpf_strip_prog_sig(prog, &sig_len);
+ if (!sysctl_bpf_signature_enable)
+ return 0;
+ if (!stripped)
+ return -ENODATA;
+ return verify_pkcs7_signature(prog->insns, prog->len * sizeof(struct sock_filter),
+ prog->insns + prog->len,
+ sig_len, VERIFY_USE_SECONDARY_KEYRING,
+ VERIFYING_MODULE_SIGNATURE,
+ NULL, NULL);
+}
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 4caf06fe4152..2ce0afb12248 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -32,6 +32,7 @@
#include <linux/bpf-netns.h>
#include <linux/rcupdate_trace.h>
#include <linux/memcontrol.h>
+#include <linux/bpf_sig.h>
#define IS_FD_ARRAY(map) ((map)->map_type == BPF_MAP_TYPE_PERF_EVENT_ARRAY || \
(map)->map_type == BPF_MAP_TYPE_CGROUP_ARRAY || \
@@ -2201,6 +2202,10 @@ static int bpf_prog_load(union bpf_attr *attr, union bpf_attr __user *uattr)
if (err < 0)
goto free_prog_sec;
+ err = bpf_check_prog_sig(prog);
+ if (err < 0)
+ goto free_prog;
+
/* run eBPF verifier */
err = bpf_check(&prog, attr, uattr);
if (err < 0)
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index c9fbdd848138..d447d26dd0eb 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -103,6 +103,9 @@
#ifdef CONFIG_LOCKUP_DETECTOR
#include <linux/nmi.h>
#endif
+#ifdef CONFIG_BPF_SIGNATURE
+#include <linux/bpf_sig.h>
+#endif /* CONFIG_BPF_SIGNATURE */
#if defined(CONFIG_SYSCTL)
@@ -2621,6 +2624,17 @@ static struct ctl_table kern_table[] = {
},
#endif
#ifdef CONFIG_BPF_SYSCALL
+#ifdef CONFIG_BPF_SIGNATURE
+ {
+ .procname = "bpf_signature_enable",
+ .data = &sysctl_bpf_signature_enable,
+ .maxlen = sizeof(sysctl_bpf_signature_enable),
+ .mode = 0644,
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = SYSCTL_ONE,
+ .extra2 = SYSCTL_ONE,
+ },
+#endif /* CONFIG_BPF_SIGNATURE */
{
.procname = "unprivileged_bpf_disabled",
.data = &sysctl_unprivileged_bpf_disabled,
--
2.11.0
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