Re: [RFC][PATCH 4/6] bpf: Introduce bpf_verify_umd_signature() kfunc

[Yonghong Song]

On 4/25/23 10:35 AM, Roberto Sassu wrote:
> From: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
>
> Introduce the bpf_verify_umd_signature() kfunc, to verify UMD-parsed
> signatures. The parameters and usage are the same as for
> bpf_verify_pkcs7_signature().
>
> Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
> ---
>   kernel/trace/bpf_trace.c | 69 ++++++++++++++++++++++++++++++++--------
>   1 file changed, 55 insertions(+), 14 deletions(-)
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index e8da032bb6f..c9cae337596 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -1271,7 +1271,7 @@ __bpf_kfunc struct bpf_key *bpf_lookup_user_key(u32 serial, u64 flags)
>    * The key pointer is marked as invalid, to prevent bpf_key_put() from
>    * attempting to decrement the key reference count on that pointer. The key
>    * pointer set in such way is currently understood only by
> - * verify_pkcs7_signature().
> + * verify_pkcs7_signature() and verify_umd_signature().
>    *
>    * Set *id* to one of the values defined in include/linux/verification.h:
>    * 0 for the primary keyring (immutable keyring of system keys);
> @@ -1317,6 +1317,27 @@ __bpf_kfunc void bpf_key_put(struct bpf_key *bkey)
>   }
>   
>   #ifdef CONFIG_SYSTEM_DATA_VERIFICATION
> +static int validate_key(struct bpf_key *trusted_keyring)
> +{
> +	int ret = 0;
> +
> +	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;

The above
	if (ret < 0)
		return ret;
can be removed.

> +	}
> +
> +	return ret;
> +}
> +
>   /**
>    * bpf_verify_pkcs7_signature - verify a PKCS#7 signature
>    * @data_ptr: data to verify
> @@ -1334,19 +1355,9 @@ __bpf_kfunc int bpf_verify_pkcs7_signature(struct bpf_dynptr_kern *data_ptr,
>   {
>   	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;
> -	}
> +	ret = validate_key(trusted_keyring);
> +	if (ret < 0)
> +		return ret;
>   
>   	return verify_pkcs7_signature(data_ptr->data,
>   				      bpf_dynptr_get_size(data_ptr),
> @@ -1356,6 +1367,35 @@ __bpf_kfunc int bpf_verify_pkcs7_signature(struct bpf_dynptr_kern *data_ptr,
>   				      VERIFYING_UNSPECIFIED_SIGNATURE, NULL,
>   				      NULL);
>   }
> +
> +/**
> + * bpf_verify_umd_signature - Verify a UMD-parsed signature
> + * @data_ptr: Data to verify
> + * @sig_ptr: Signature of the data
> + * @trusted_keyring: Keyring with keys trusted for signature verification
> + *
> + * Verify the UMD-parsed 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.
> + */
> +__bpf_kfunc int bpf_verify_umd_signature(struct bpf_dynptr_kern *data_ptr,
> +					 struct bpf_dynptr_kern *sig_ptr,
> +					 struct bpf_key *trusted_keyring)
> +{
> +	int ret;
> +
> +	ret = validate_key(trusted_keyring);
> +	if (ret < 0)
> +		return ret;
> +
> +	return verify_umd_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();
> @@ -1366,6 +1406,7 @@ 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)
> +BTF_ID_FLAGS(func, bpf_verify_umd_signature, KF_SLEEPABLE)
>   #endif
>   BTF_SET8_END(key_sig_kfunc_set)
>