diff mbox series

[v10,6/9] bpf: Add bpf_verify_pkcs7_signature() kfunc

Message ID 20220810165932.2143413-7-roberto.sassu@huawei.com (mailing list archive)
State Accepted
Commit 865b0566d8f1a0c3937e5eb4bd6ba4ef03e7e98c
Headers show
Series bpf: Add kfuncs for PKCS#7 signature verification | expand

Commit Message

Roberto Sassu Aug. 10, 2022, 4:59 p.m. UTC
Add the bpf_verify_pkcs7_signature() kfunc, to give eBPF security modules
the ability to check the validity of a signature against supplied data, by
using user-provided or system-provided keys as trust anchor.

The new kfunc makes it possible to enforce mandatory policies, as eBPF
programs might be allowed to make security decisions only based on data
sources the system administrator approves.

The caller should provide the data to be verified and the signature as eBPF
dynamic pointers (to minimize the number of parameters) and a bpf_key
structure containing a reference to the keyring with keys trusted for
signature verification, obtained from bpf_lookup_user_key() or
bpf_lookup_system_key().

For bpf_key structures obtained from the former lookup function,
bpf_verify_pkcs7_signature() completes the permission check deferred by
that function by calling key_validate(). key_task_permission() is already
called by the PKCS#7 code.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 kernel/trace/bpf_trace.c | 45 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

Comments

KP Singh Aug. 12, 2022, 12:54 a.m. UTC | #1
On Wed, Aug 10, 2022 at 7:01 PM Roberto Sassu <roberto.sassu@huawei.com> wrote:
>
> Add the bpf_verify_pkcs7_signature() kfunc, to give eBPF security modules
> the ability to check the validity of a signature against supplied data, by
> using user-provided or system-provided keys as trust anchor.
>
> The new kfunc makes it possible to enforce mandatory policies, as eBPF
> programs might be allowed to make security decisions only based on data
> sources the system administrator approves.
>
> The caller should provide the data to be verified and the signature as eBPF
> dynamic pointers (to minimize the number of parameters) and a bpf_key
> structure containing a reference to the keyring with keys trusted for
> signature verification, obtained from bpf_lookup_user_key() or
> bpf_lookup_system_key().
>
> For bpf_key structures obtained from the former lookup function,
> bpf_verify_pkcs7_signature() completes the permission check deferred by
> that function by calling key_validate(). key_task_permission() is already
> called by the PKCS#7 code.
>
> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>

Acked-by: KP Singh <kpsingh@kernel.org>
diff mbox series

Patch

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index a607bb0be738..d575e026e698 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1298,12 +1298,57 @@  void bpf_key_put(struct bpf_key *bkey)
 	kfree(bkey);
 }
 
+#ifdef CONFIG_SYSTEM_DATA_VERIFICATION
+/**
+ * bpf_verify_pkcs7_signature - verify a PKCS#7 signature
+ * @data_ptr: data to verify
+ * @sig_ptr: signature of the data
+ * @trusted_keyring: keyring with keys trusted for signature verification
+ *
+ * Verify the PKCS#7 signature *sig_ptr* against the supplied *data_ptr*
+ * with keys in a keyring referenced by *trusted_keyring*.
+ *
+ * Return: 0 on success, a negative value on error.
+ */
+int bpf_verify_pkcs7_signature(struct bpf_dynptr_kern *data_ptr,
+			       struct bpf_dynptr_kern *sig_ptr,
+			       struct bpf_key *trusted_keyring)
+{
+	int ret;
+
+	if (trusted_keyring->has_ref) {
+		/*
+		 * Do the permission check deferred in bpf_lookup_user_key().
+		 * See bpf_lookup_user_key() for more details.
+		 *
+		 * A call to key_task_permission() here would be redundant, as
+		 * it is already done by keyring_search() called by
+		 * find_asymmetric_key().
+		 */
+		ret = key_validate(trusted_keyring->key);
+		if (ret < 0)
+			return ret;
+	}
+
+	return verify_pkcs7_signature(data_ptr->data,
+				      bpf_dynptr_get_size(data_ptr),
+				      sig_ptr->data,
+				      bpf_dynptr_get_size(sig_ptr),
+				      trusted_keyring->key,
+				      VERIFYING_UNSPECIFIED_SIGNATURE, NULL,
+				      NULL);
+}
+#endif /* CONFIG_SYSTEM_DATA_VERIFICATION */
+
 __diag_pop();
 
 BTF_SET8_START(key_sig_kfunc_set)
 BTF_ID_FLAGS(func, bpf_lookup_user_key, KF_ACQUIRE | KF_RET_NULL | KF_SLEEPABLE)
 BTF_ID_FLAGS(func, bpf_lookup_system_key, KF_ACQUIRE | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_key_put, KF_RELEASE)
+#ifdef CONFIG_SYSTEM_DATA_VERIFICATION
+BTF_ID_FLAGS(func, bpf_verify_pkcs7_signature, KF_SLEEPABLE)
+#endif
 BTF_SET8_END(key_sig_kfunc_set)
 
 static const struct btf_kfunc_id_set bpf_key_sig_kfunc_set = {