[PATCH bpf-next v2 10/11] selftests/bpf: Add tests for bpf keyring in signed loader

[Daniel Borkmann <daniel@iogearbox.net>]

bpf_keyring_provisioned walks the keyring through its whole lifecycle in
one boot for ease of testing. It enrolls a freshly generated key into the
bpf keyring, confirms a load is still refused with -ENOKEY while the keyring
carries no restriction, then restricts it, and only then does the same
signed BPF program load with the bpf keyring. A caller-supplied keyring is
asserted to be refused both before and after the restriction, since what
refuses it is bpf.keyring_unsealed=1 rather than the state of the keyring.

Unsealing is a boot-time decision which also refuses the session keyring
that every other subtest here signs against, so such a boot goes straight
to this test and a regular run covers the rest. Without bpf.keyring_unsealed=1
on the vmtest guest command line the subtest is not registered at all, since
a sealed keyring can never be provisioned.

Regular run:

  # LDLIBS=-static PKG_CONFIG='pkg-config --static' ./vmtest.sh -- ./test_progs -t signed_loader
  [...]
  #425/12  signed_loader/signature_zero_size:OK
  #425/13  signed_loader/signature_bad_keyring:OK
  #425/14  signed_loader/bpf_keyring_sealed:OK
  [...]
  #425/30  signed_loader/signed_map_by_fd_rejected:OK
  #425/31  signed_loader/signed_sparse_fd_array_rejected:OK
  #425     signed_loader:OK
  Summary: 1/31 PASSED, 0 SKIPPED, 0/0 FAILED

Unsealed run:

  # KERNEL_CMDLINE_EXTRA="bpf.keyring_unsealed=1" \
    LDLIBS=-static PKG_CONFIG='pkg-config --static' ./vmtest.sh -- ./test_progs -t signed_loader
  #425/1   signed_loader/bpf_keyring_provisioned:OK
  #425     signed_loader:OK
  Summary: 1/1 PASSED, 0 SKIPPED, 0/0 FAILED

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
---
 .../selftests/bpf/prog_tests/signed_loader.c  | 244 ++++++++++++++++--
 1 file changed, 217 insertions(+), 27 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/signed_loader.c b/tools/testing/selftests/bpf/prog_tests/signed_loader.c
index b467221d3e58..620a6d22a759 100644
--- a/tools/testing/selftests/bpf/prog_tests/signed_loader.c
+++ b/tools/testing/selftests/bpf/prog_tests/signed_loader.c
@@ -43,9 +43,9 @@ enum {
 /* FIPS-204 ML-DSA-87 signature size, see include/crypto/mldsa.h. */
 #define MLDSA87_SIGNATURE_SIZE	4627
 
-static int load_loader(const void *insns, __u32 insns_sz, int map_fd,
-		       const void *sig, __u32 sig_sz, __s32 keyring_id,
-		       __u32 fd_array_cnt)
+static int load_loader_log(const void *insns, __u32 insns_sz, int map_fd,
+			   const void *sig, __u32 sig_sz, __s32 keyring_id,
+			   __u32 fd_array_cnt, char *log_buf, __u32 log_sz)
 {
 	union bpf_attr attr;
 	int fd;
@@ -57,18 +57,31 @@ static int load_loader(const void *insns, __u32 insns_sz, int map_fd,
 	attr.license = ptr_to_u64("Dual BSD/GPL");
 	attr.prog_flags = BPF_F_SLEEPABLE;
 	attr.fd_array = ptr_to_u64(&map_fd);
+	attr.fd_array_cnt = fd_array_cnt;
 	if (sig) {
 		attr.signature = ptr_to_u64(sig);
 		attr.signature_size = sig_sz;
 		attr.keyring_id = keyring_id;
 	}
-	attr.fd_array_cnt = fd_array_cnt;
+	if (log_buf) {
+		attr.log_level = 1;
+		attr.log_buf = ptr_to_u64(log_buf);
+		attr.log_size = log_sz;
+	}
 	memcpy(attr.prog_name, "__loader.prog", sizeof("__loader.prog"));
 	fd = syscall(__NR_bpf, BPF_PROG_LOAD, &attr,
 		     offsetofend(union bpf_attr, keyring_id));
 	return fd < 0 ? -errno : fd;
 }
 
+static int load_loader(const void *insns, __u32 insns_sz, int map_fd,
+		       const void *sig, __u32 sig_sz, __s32 keyring_id,
+		       __u32 fd_array_cnt)
+{
+	return load_loader_log(insns, insns_sz, map_fd, sig, sig_sz, keyring_id,
+			       fd_array_cnt, NULL, 0);
+}
+
 static int run_gen_loader(const void *insns, __u32 insns_sz,
 			  const void *data, __u32 data_sz,
 			  const void *excl, __u32 excl_sz,
@@ -203,6 +216,7 @@ static int sign_buf_digest(const char *dir, const void *buf, __u32 len,
 	fd = mkstemp(data_tmpl);
 	if (fd < 0)
 		return -errno;
+	snprintf(sigpath, sizeof(sigpath), "%s.p7s", data_tmpl);
 	if (write(fd, buf, len) != (ssize_t)len) {
 		close(fd);
 		ret = -EIO;
@@ -227,30 +241,28 @@ static int sign_buf_digest(const char *dir, const void *buf, __u32 len,
 		goto out;
 	}
 
-	snprintf(sigpath, sizeof(sigpath), "%s.p7s", data_tmpl);
 	if (stat(sigpath, &st) < 0) {
 		ret = -errno;
 		goto out;
 	}
 	if (st.st_size > (off_t)*sig_sz) {
 		ret = -E2BIG;
-		goto out_sig;
+		goto out;
 	}
 	fd = open(sigpath, O_RDONLY);
 	if (fd < 0) {
 		ret = -errno;
-		goto out_sig;
+		goto out;
 	}
 	if (read(fd, sig, st.st_size) != st.st_size) {
 		close(fd);
 		ret = -EIO;
-		goto out_sig;
+		goto out;
 	}
 	close(fd);
 	*sig_sz = st.st_size;
-out_sig:
-	unlink(sigpath);
 out:
+	unlink(sigpath);
 	unlink(data_tmpl);
 	return ret;
 }
@@ -562,7 +574,6 @@ static void signature_failure_logs(void)
 	static const __u8 junk[64] = { 0x30, 0x42, 0x13, 0x37, };
 	char log_buf[1024] = {};
 	struct gen_loader_fixture f;
-	union bpf_attr attr;
 	int fd;
 
 	if (gen_loader_fixture_init(&f) == 0) {
@@ -571,22 +582,9 @@ static void signature_failure_logs(void)
 		 * failure is reported through the verifier log. A present-but-
 		 * invalid signature is rejected and the log says why.
 		 */
-		memset(&attr, 0, sizeof(attr));
-		attr.prog_type = BPF_PROG_TYPE_SYSCALL;
-		attr.insns = ptr_to_u64(f.gopts.insns);
-		attr.insn_cnt = f.gopts.insns_sz / sizeof(struct bpf_insn);
-		attr.license = ptr_to_u64("Dual BSD/GPL");
-		attr.prog_flags = BPF_F_SLEEPABLE;
-		attr.signature = ptr_to_u64(junk);
-		attr.signature_size = sizeof(junk);
-		attr.keyring_id = KEY_SPEC_SESSION_KEYRING;
-		attr.log_level = 1;
-		attr.log_buf = ptr_to_u64(log_buf);
-		attr.log_size = sizeof(log_buf);
-		memcpy(attr.prog_name, "__loader.prog", sizeof("__loader.prog"));
-
-		fd = syscall(__NR_bpf, BPF_PROG_LOAD, &attr,
-			     offsetofend(union bpf_attr, keyring_id));
+		fd = load_loader_log(f.gopts.insns, f.gopts.insns_sz, -1, junk,
+				     sizeof(junk), KEY_SPEC_SESSION_KEYRING, 0,
+				     log_buf, sizeof(log_buf));
 		ASSERT_LT(fd, 0, "invalid signature rejected at load");
 		if (fd >= 0)
 			close(fd);
@@ -706,6 +704,23 @@ static int bpf_keyring_lookup(int *nr_keys)
 	return serial;
 }
 
+static long keyctl_ret(int cmd, unsigned long arg2, unsigned long arg3)
+{
+	long ret = syscall(__NR_keyctl, cmd, arg2, arg3);
+
+	return ret < 0 ? -errno : ret;
+}
+
+/*
+ * What the bpf keyring still needs once it got provisioned: KEY_POS_SEARCH
+ * for the in-kernel search during verification, and the user view/read bits
+ * so it stays visible in /proc/keys, rest is dropped so the enrolled is
+ * therefore final.
+ */
+#define BPF_KEYRING_PERM_LOCKED		0x08030000
+/* What bpf_keyring_init() grants at boot. */
+#define BPF_KEYRING_PERM_INITIAL	0x082f0000
+
 static void bpf_keyring_sealed(void)
 {
 	static const __u8 junk[64] = {};
@@ -735,6 +750,176 @@ static void bpf_keyring_sealed(void)
 	gen_loader_fixture_fini(&f);
 }
 
+static int try_load(const struct gen_loader_fixture *f, const void *sig,
+		    __u32 sig_sz, __s32 keyring_id, char *log_buf, __u32 log_sz)
+{
+	int map_fd, prog_fd;
+
+	map_fd = setup_meta_map(f);
+	if (!ASSERT_OK_FD(map_fd, "meta_map"))
+		return map_fd;
+	prog_fd = load_loader_log(f->gopts.insns, f->gopts.insns_sz, map_fd,
+				  sig, sig_sz, keyring_id, 1, log_buf, log_sz);
+	close(map_fd);
+	if (prog_fd >= 0)
+		close(prog_fd);
+	return prog_fd;
+}
+
+/*
+ * This needs bpf.keyring_unsealed=1 on the guest kernel command line, which
+ * vmtest.sh can pass via KERNEL_CMDLINE_EXTRA. There is no way to unseal the
+ * keyring from here, so without it the test skips. It also only works once
+ * per boot, as restricting a keyring cannot be undone.
+ */
+static void bpf_keyring_provisioned(void)
+{
+	char dir_tmpl[] = "/tmp/bpfkeyringXXXXXX";
+	char bad_tmpl[] = "/tmp/bpfkeyringbadXXXXXX";
+	__u8 *sig = NULL, *bad = NULL, *buf = NULL;
+	int serial, err;
+	int nr_keys = 0, der_fd = -1;
+	struct gen_loader_fixture f;
+	__u32 sig_sz = 8192, bad_sz;
+	bool have_fixture = false;
+	char *dir, *bad_dir = NULL;
+	char log_buf[1024] = {};
+	char path[PATH_MAX];
+	__u8 der[4096];
+	ssize_t der_sz;
+
+	serial = bpf_keyring_lookup(&nr_keys);
+	if (serial < 0) {
+		printf("%s:SKIP:no bpf keyring (needs CONFIG_KEYS)\n", __func__);
+		test__skip();
+		return;
+	}
+	if (nr_keys != 0) {
+		printf("%s:SKIP:the bpf keyring has already been provisioned\n",
+		       __func__);
+		test__skip();
+		return;
+	}
+
+	dir = mkdtemp(dir_tmpl);
+	if (!ASSERT_OK_PTR(dir, "mkdtemp"))
+		return;
+	if (!ASSERT_OK(run_setup("genkey", dir), "verify_sig_setup genkey"))
+		goto rmdir;
+
+	snprintf(path, sizeof(path), "%s/signing_key.der", dir);
+	der_fd = open(path, O_RDONLY);
+	if (!ASSERT_OK_FD(der_fd, "open signing_key.der"))
+		goto rmdir;
+	der_sz = read(der_fd, der, sizeof(der));
+	close(der_fd);
+	if (!ASSERT_GT(der_sz, 0, "read signing_key.der"))
+		goto rmdir;
+
+	err = syscall(__NR_add_key, "asymmetric", "", der, (size_t)der_sz,
+		      serial);
+	if (err < 0 && errno == EPERM) {
+		printf("%s:SKIP:the bpf keyring is sealed, need bpf.keyring_unsealed=1\n",
+		       __func__);
+		test__skip();
+		goto rmdir;
+	}
+	if (!ASSERT_GE(err, 0, "add the signing key to the bpf keyring"))
+		goto rmdir;
+
+	sig = malloc(sig_sz);
+	if (!ASSERT_OK_PTR(sig, "sig buf"))
+		goto out;
+	have_fixture = true;
+	if (gen_loader_fixture_init(&f) != 0)
+		goto out;
+
+	buf = malloc((size_t)f.gopts.insns_sz + f.data_sz);
+	if (!ASSERT_OK_PTR(buf, "signbuf"))
+		goto out;
+	memcpy(buf, f.gopts.insns, f.gopts.insns_sz);
+	memcpy(buf + f.gopts.insns_sz, f.blob, f.data_sz);
+	if (!ASSERT_OK(sign_buf(dir, buf, f.gopts.insns_sz + f.data_sz, sig,
+				&sig_sz), "sign insns||metadata"))
+		goto out;
+
+	ASSERT_EQ(try_load(&f, sig, sig_sz, BPF_KEYRING_BPF, NULL, 0), -ENOKEY,
+		  "unrestricted keyring still not consulted");
+
+	ASSERT_EQ(try_load(&f, sig, sig_sz, KEY_SPEC_SESSION_KEYRING, NULL, 0),
+		  -EPERM, "caller-supplied keyring refused before provisioning");
+
+	if (!ASSERT_OK(syscall(__NR_keyctl, KEYCTL_RESTRICT_KEYRING, serial,
+			       NULL, NULL), "restrict bpf keyring"))
+		goto out;
+
+	if (!ASSERT_OK_FD(try_load(&f, sig, sig_sz, BPF_KEYRING_BPF, NULL, 0),
+			  "load signed by a key in the .bpf keyring"))
+		goto out;
+
+	bad_dir = mkdtemp(bad_tmpl);
+	if (!ASSERT_OK_PTR(bad_dir, "mkdtemp unenrolled"))
+		goto out;
+	if (!ASSERT_OK(run_setup("genkey", bad_dir), "verify_sig_setup genkey unenrolled"))
+		goto out;
+	bad_sz = 8192;
+	bad = malloc(bad_sz);
+	if (!ASSERT_OK_PTR(bad, "bad sig buf"))
+		goto out;
+	if (!ASSERT_OK(sign_buf(bad_dir, buf, f.gopts.insns_sz + f.data_sz, bad,
+				&bad_sz), "sign with an unenrolled key"))
+		goto out;
+
+	ASSERT_EQ(try_load(&f, bad, bad_sz, BPF_KEYRING_BPF, log_buf,
+			   sizeof(log_buf)), -ENOKEY,
+		  "key outside the bpf keyring refused");
+	ASSERT_HAS_SUBSTR(log_buf, "signature verification failed",
+			  "the bpf keyring was consulted");
+
+	f.blob[0] ^= 0xff;
+	err = try_load(&f, sig, sig_sz, BPF_KEYRING_BPF, NULL, 0);
+	f.blob[0] ^= 0xff;
+	ASSERT_EQ(err, -EKEYREJECTED, "tampered metadata refused");
+
+	ASSERT_EQ(try_load(&f, sig, sig_sz, KEY_SPEC_SESSION_KEYRING, NULL, 0),
+		  -EPERM, "caller-supplied keyring refused once .bpf is in use");
+
+	err = keyctl_ret(KEYCTL_UNLINK, KEY_SPEC_SESSION_KEYRING, serial);
+	ASSERT_EQ(err, -ENOENT, "keyring writable while the user bits are there");
+
+	err = keyctl_ret(KEYCTL_SETPERM, serial, BPF_KEYRING_PERM_LOCKED);
+	if (!ASSERT_OK(err, "drop the user bits on the bpf keyring"))
+		goto out;
+
+	ASSERT_OK_FD(try_load(&f, sig, sig_sz, BPF_KEYRING_BPF, NULL, 0),
+		     "load still verified against the locked keyring");
+
+	err = keyctl_ret(KEYCTL_UNLINK, KEY_SPEC_SESSION_KEYRING, serial);
+	ASSERT_EQ(err, -EACCES, "unlink refused");
+	err = keyctl_ret(KEYCTL_CLEAR, serial, 0);
+	ASSERT_EQ(err, -EACCES, "clear refused");
+	err = keyctl_ret(KEYCTL_REVOKE, serial, 0);
+	ASSERT_EQ(err, -EACCES, "revoke refused");
+	err = keyctl_ret(KEYCTL_INVALIDATE, serial, 0);
+	ASSERT_EQ(err, -EACCES, "invalidate refused");
+	err = keyctl_ret(KEYCTL_SET_TIMEOUT, serial, 1);
+	ASSERT_EQ(err, -EACCES, "timeout refused");
+	err = keyctl_ret(KEYCTL_SETPERM, serial, BPF_KEYRING_PERM_INITIAL);
+	ASSERT_EQ(err, -EACCES, "the bits cannot be granted back");
+
+	ASSERT_EQ(bpf_keyring_lookup(&nr_keys), serial, "keyring still there");
+	ASSERT_EQ(nr_keys, 1, "the enrolled key survived");
+out:
+	if (have_fixture)
+		gen_loader_fixture_fini(&f);
+	genkey_dir_fini(bad_dir);
+	free(buf);
+	free(bad);
+	free(sig);
+rmdir:
+	genkey_dir_fini(dir);
+}
+
 /*
  * A signed loader must ignore ctx-supplied map dimensions: the host cannot
  * resize a signed program's maps via the loader ctx. Drive a one-map program
@@ -1971,6 +2156,11 @@ static void signed_module_kfunc_rejected(void)
 
 void test_signed_loader(void)
 {
+	if (keyring_unsealed_boot()) {
+		if (test__start_subtest("bpf_keyring_provisioned"))
+			bpf_keyring_provisioned();
+		return;
+	}
 	if (test__start_subtest("loadtime_no_map"))
 		loadtime_no_map();
 	if (test__start_subtest("loadtime_with_map"))
-- 
2.43.0