linux-kernel - Re: [PATCH v7 4/5] keys: asymmetric: Add tpm2_key

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Date: Thu, 20 Jun 2024 03:23:20 +0300
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Herbert Xu" <herbert@...dor.apana.org.au>
Cc: <linux-integrity@...r.kernel.org>, <keyrings@...r.kernel.org>,
 <Andreas.Fuchs@...ineon.com>, "James Prestwood" <prestwoj@...il.com>,
 "David Woodhouse" <dwmw2@...radead.org>, "Eric Biggers"
 <ebiggers@...nel.org>, "James Bottomley"
 <James.Bottomley@...senpartnership.com>, <linux-crypto@...r.kernel.org>,
 "Stefan Berger" <stefanb@...ux.ibm.com>, "Lennart Poettering"
 <lennart@...ttering.net>, "David S. Miller" <davem@...emloft.net>, "open
 list" <linux-kernel@...r.kernel.org>, "David Howells"
 <dhowells@...hat.com>, "Ard Biesheuvel" <ardb@...nel.org>, "Mario
 Limonciello" <mario.limonciello@....com>
Subject: Re: [PATCH v7 4/5] keys: asymmetric: Add tpm2_key_rsa

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