Re: [PATCH v7 4/5] keys: asymmetric: Add tpm2_key_rsa

["Jarkko Sakkinen" <jarkko@kernel.org>]

On Fri Jun 7, 2024 at 1:58 PM EEST, Herbert Xu wrote:
> On Wed, May 29, 2024 at 12:08:09AM +0300, Jarkko Sakkinen wrote:
> >
> > +/*
> > + * Sign operation is an encryption using the TPM's private key. With RSA the
> > + * only difference between encryption and decryption is where the padding goes.
> > + * Since own padding can be used, TPM2_RSA_Decrypt can be repurposed to do
> > + * encryption.
> > + */
> > +static int tpm2_key_rsa_sign(struct tpm_chip *chip, struct tpm2_key *key,
> > +			     struct kernel_pkey_params *params,
> > +			     const void *in, void *out)
> > +{
> > +	const off_t o = key->priv_len + 2 + sizeof(*key->desc);
> > +	const struct tpm2_rsa_parms *p =
> > +		(const struct tpm2_rsa_parms *)&key->data[o];
> > +	const u16 mod_size = be16_to_cpu(p->modulus_size);
> > +	const struct rsa_asn1_template *asn1;
> > +	u32 in_len = params->in_len;
> > +	void *asn1_wrapped = NULL;
> > +	u8 *padded;
> > +	int ret;
> > +
> > +	if (strcmp(params->encoding, "pkcs1") != 0) {
> > +		ret = -ENOPKG;
> > +		goto err;
> > +	}
> > +
> > +	if (params->hash_algo) {
> > +		asn1 = rsa_lookup_asn1(params->hash_algo);
>
> Could you please explain why this can't be done through pkcs1pad
> instead of going to raw RSA?

Sorry was away couple of weeks from here. I replace this with TPM2_Sign
as is done already in the ECDSA module, so I guess that is a "yes".

BR, Jarkko