On Fri, Sep 9, 2022 at 2:09 PM Roberto Sassu roberto.sassu@huaweicloud.com wrote:
From: Roberto Sassu roberto.sassu@huawei.com
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
kernel/trace/bpf_trace.c | 45 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 45 insertions(+)
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index ab183dbaa8d1..9df53c40cffd 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -1294,12 +1294,57 @@ 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);+}
This seems to work if the data that needs to be verified and the signature is allocated onto the map.
For BPF program signing, the signature will be void * pointer (and length) in a struct in the kernel
+++ b/include/uapi/linux/bpf.h @@ -1383,6 +1383,8 @@ 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; + __u32 signature_size; };
Something like this in the bpf_prog_aux struct which is passed to security_bpf_prog_alloc.
Now creating a dynptr to use with this kfunc does not work:
bpf_dynptr_from_mem(aux->signature, aux->signature_size, 0, &sig_ptr);
So one has to copy kernel data into a map and then create dynptrs. Would you be able to update the dynptr logic to handle this case too? (follow up is okay too).
- KP
+#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 = {
2.25.1