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

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Date: Fri, 7 Jun 2024 18:58:18 +0800
From: Herbert Xu <herbert@...dor.apana.org.au>
To: Jarkko Sakkinen <jarkko@...nel.org>
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 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?

Thanks,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt