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

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Message-Id: <D1HD3CW2C38O.3DTAGBUHF8AO9@kernel.org>
Date: Fri, 24 May 2024 01:02:45 +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 12:52 AM EEST, Jarkko Sakkinen wrote:
> 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_key.c.
> > > +	 */
> > > +	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.

That said, zero issues with the interface, just pointing out the
part that is not right, and should be fixed.

I mean I have three layers: this, rsa-pcks1 and rsa. How I can be
sure that either of two layers below never ever up until sun melts
will do any changes that would break, with the data that I put
there? Is this a contract that will hold forever?

This is concerning so I have to point this out.

BR, Jarkko