linux-kernel - Re: [PATCH v5 5/5] keys: asymmetric: ASYMMETRIC_TPM2_KEY_RSA

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Message-Id: <D1HCVOZ1IN7S.1SUZ75QRE8QUZ@kernel.org>
Date: Fri, 24 May 2024 00:52:44 +0300
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Jarkko Sakkinen" <jarkko@...nel.org>, "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>,
 "David S. Miller" <davem@...emloft.net>, "open list"
 <linux-kernel@...r.kernel.org>, "David Howells" <dhowells@...hat.com>,
 "James Bottomley" <James.Bottomley@...senPartnership.com>, "Stefan Berger"
 <stefanb@...ux.ibm.com>, "Ard Biesheuvel" <ardb@...nel.org>, "Mario
 Limonciello" <mario.limonciello@....com>
Subject: Re: [PATCH v5 5/5] keys: asymmetric:
 ASYMMETRIC_TPM2_KEY_RSA_SUBTYPE

On Fri May 24, 2024 at 12:39 AM EEST, Jarkko Sakkinen wrote:
> On Fri May 24, 2024 at 12:25 AM EEST, Jarkko Sakkinen wrote:
> > +	/*
> > +	 * ABI requires this according include/crypto/akcipher.h, which says
> > +	 * that there is epilogue with algorithm OID and parameters length.
> > +	 * Neither size nor semantics is documented *anywhere*, and there's no
> > +	 * struct to hold them.
> > +	 *
> > +	 * So zeroing out the last eight bytes after the key blob seems like the
> > +	 * best bet, given no better (or any) information. The size of the
> > +	 * parameters (two u32's) was found from crypto/asymmetric/public_keyc.
> > +	 */
> > +	memset(work, 0, 8);
>
> This is a mystery (or nightmare).

This is from akchiper_alg documentation:

 * @set_pub_key: Function invokes the algorithm specific set public key
 *		function, which knows how to decode and interpret
 *		the BER encoded public key and parameters

No struct, no size information and no description what they are used for.

Can we get these properly documented? My documentation at the moment
is grep and kprobes, literally.

BR, Jarkko