[PATCH bpf-next 1/3] bpf: add signature to eBPF instructions

Matteo Croce
2021-12-03T19:19:17Z

From: Matteo Croce <mcroce@microsoft.com>

When loading a BPF program, pass a signature which is used to validate
the instructions.
The signature type is the same used to validate the kernel modules.

This happens when loading a program with, respectively, an invalid and
a valid signature:

# ./core-bad
[ 8524.417567] Invalid BPF signature for '__loader.prog': -EKEYREJECTED
failed to open and/or load BPF object
# ./core-ok

Signed-off-by: Matteo Croce <mcroce@microsoft.com>
---
crypto/asymmetric_keys/asymmetric_type.c | 1 +
crypto/asymmetric_keys/pkcs7_verify.c | 7 +++-
include/linux/verification.h | 1 +
include/uapi/linux/bpf.h | 2 +
kernel/bpf/Kconfig | 8 ++++
kernel/bpf/syscall.c | 47 +++++++++++++++++++++---
6 files changed, 59 insertions(+), 7 deletions(-)

diff --git a/crypto/asymmetric_keys/asymmetric_type.c b/crypto/asymmetric_keys/asymmetric_type.c
index ad8af3d70ac0..e4f2fee19c5f 100644
--- a/crypto/asymmetric_keys/asymmetric_type.c
+++ b/crypto/asymmetric_keys/asymmetric_type.c
@@ -26,6 +26,7 @@ const char *const key_being_used_for[NR__KEY_BEING_USED_FOR] = {
[VERIFYING_KEY_SIGNATURE] = "key sig",
[VERIFYING_KEY_SELF_SIGNATURE] = "key self sig",
[VERIFYING_UNSPECIFIED_SIGNATURE] = "unspec sig",
+ [VERIFYING_BPF_SIGNATURE] = "bpf sig",
};
EXPORT_SYMBOL_GPL(key_being_used_for);

diff --git a/crypto/asymmetric_keys/pkcs7_verify.c b/crypto/asymmetric_keys/pkcs7_verify.c
index 0b4d07aa8811..ab645f23c021 100644
--- a/crypto/asymmetric_keys/pkcs7_verify.c
+++ b/crypto/asymmetric_keys/pkcs7_verify.c
@@ -411,12 +411,15 @@ int pkcs7_verify(struct pkcs7_message *pkcs7,

switch (usage) {
case VERIFYING_MODULE_SIGNATURE:
+ case VERIFYING_BPF_SIGNATURE:
if (pkcs7->data_type != OID_data) {
- pr_warn("Invalid module sig (not pkcs7-data)\n");
+ pr_warn("Invalid %s (not pkcs7-data)\n",
+ key_being_used_for[usage]);
return -EKEYREJECTED;
}
if (pkcs7->have_authattrs) {
- pr_warn("Invalid module sig (has authattrs)\n");
+ pr_warn("Invalid %s (has authattrs)\n",
+ key_being_used_for[usage]);
return -EKEYREJECTED;
}
break;
diff --git a/include/linux/verification.h b/include/linux/verification.h
index a655923335ae..71482644eea0 100644
--- a/include/linux/verification.h
+++ b/include/linux/verification.h
@@ -27,6 +27,7 @@ enum key_being_used_for {
VERIFYING_KEY_SIGNATURE,
VERIFYING_KEY_SELF_SIGNATURE,
VERIFYING_UNSPECIFIED_SIGNATURE,
+ VERIFYING_BPF_SIGNATURE,
NR__KEY_BEING_USED_FOR
};
extern const char *const key_being_used_for[NR__KEY_BEING_USED_FOR];
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index c26871263f1f..bbb4435c7586 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -1346,6 +1346,8 @@ union bpf_attr {
__aligned_u64 fd_array; /* array of FDs */
__aligned_u64 core_relos;
__u32 core_relo_rec_size; /* sizeof(struct bpf_core_relo) */
+ __aligned_u64 signature; /* instruction's signature */
+ __u32 sig_len; /* signature size */
};

struct { /* anonymous struct used by BPF_OBJ_* commands */
diff --git a/kernel/bpf/Kconfig b/kernel/bpf/Kconfig
index d24d518ddd63..735979bb8672 100644
--- a/kernel/bpf/Kconfig
+++ b/kernel/bpf/Kconfig
@@ -79,6 +79,14 @@ config BPF_UNPRIV_DEFAULT_OFF

If you are unsure how to answer this question, answer Y.

+config BPF_SIG
+ bool "BPF signature verification"
+ select SYSTEM_DATA_VERIFICATION
+ depends on BPF_SYSCALL
+ help
+ Check BPF programs for valid signatures upon load: the signature
+ is passed via the bpf() syscall together with the instructions.
+
source "kernel/bpf/preload/Kconfig"

config BPF_LSM
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index b3ada4085f85..5aaa74a72b46 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -32,6 +32,10 @@
#include <linux/rcupdate_trace.h>
#include <linux/memcontrol.h>

+#ifdef CONFIG_BPF_SIG
+#include <linux/verification.h>
+#endif
+
#define IS_FD_ARRAY(map) ((map)->map_type == BPF_MAP_TYPE_PERF_EVENT_ARRAY || \
(map)->map_type == BPF_MAP_TYPE_CGROUP_ARRAY || \
(map)->map_type == BPF_MAP_TYPE_ARRAY_OF_MAPS)
@@ -2184,7 +2188,7 @@ static bool is_perfmon_prog_type(enum bpf_prog_type prog_type)
}

/* last field in 'union bpf_attr' used by this command */
-#define BPF_PROG_LOAD_LAST_FIELD core_relo_rec_size
+#define BPF_PROG_LOAD_LAST_FIELD sig_len

static int bpf_prog_load(union bpf_attr *attr, bpfptr_t uattr)
{
@@ -2302,6 +2306,43 @@ static int bpf_prog_load(union bpf_attr *attr, bpfptr_t uattr)
bpf_prog_insn_size(prog)) != 0)
goto free_prog_sec;

+ err = bpf_obj_name_cpy(prog->aux->name, attr->prog_name,
+ sizeof(attr->prog_name));
+ if (err < 0)
+ goto free_prog_sec;
+
+#ifdef CONFIG_BPF_SIG
+ if (attr->sig_len) {
+ char *signature;
+
+ signature = kmalloc(attr->sig_len, GFP_USER);
+ if (!signature) {
+ err = -ENOMEM;
+ goto free_prog_sec;
+ }
+
+ if (copy_from_user(signature, (char *)attr->signature, attr->sig_len)) {
+ err = -EFAULT;
+ kfree(signature);
+ goto free_prog_sec;
+ }
+
+ err = verify_pkcs7_signature(prog->insns,
+ prog->len * sizeof(struct bpf_insn),
+ signature, attr->sig_len,
+ VERIFY_USE_SECONDARY_KEYRING,
+ VERIFYING_BPF_SIGNATURE,
+ NULL, NULL);
+ kfree(signature);
+
+ if (err) {
+ pr_warn("Invalid BPF signature for '%s': %pe\n",
+ prog->aux->name, ERR_PTR(err));
+ goto free_prog_sec;
+ }
+ }
+#endif
+
prog->orig_prog = NULL;
prog->jited = 0;

@@ -2320,10 +2361,6 @@ static int bpf_prog_load(union bpf_attr *attr, bpfptr_t uattr)
goto free_prog_sec;

prog->aux->load_time = ktime_get_boottime_ns();
- err = bpf_obj_name_cpy(prog->aux->name, attr->prog_name,
- sizeof(attr->prog_name));
- if (err < 0)
- goto free_prog_sec;

/* run eBPF verifier */
err = bpf_check(&prog, attr, uattr);
--
2.33.1