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

[Roberto Sassu]

On Tue, 2023-04-25 at 14:25 -0700, Yonghong Song wrote:
> 
> 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.

Right, thanks!

Roberto

> > +	}
> > +
> > +	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)
> >