linux-kernel - Re: [PATCH v2 2/3] tpm: Address !chip->auth in tpm_buf_append

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Message-Id: <D2GK2755HE3O.2IGY7W4280Z90@kernel.org>
Date: Thu, 04 Jul 2024 09:53:40 +0300
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "James Bottomley" <James.Bottomley@...senPartnership.com>,
 <linux-integrity@...r.kernel.org>
Cc: "Thorsten Leemhuis" <regressions@...mhuis.info>, "Linus Torvalds"
 <torvalds@...ux-foundation.org>, <stable@...r.kernel.org>, "Stefan Berger"
 <stefanb@...ux.ibm.com>, "Peter Huewe" <peterhuewe@....de>, "Jason
 Gunthorpe" <jgg@...pe.ca>, "Mimi Zohar" <zohar@...ux.ibm.com>, "David
 Howells" <dhowells@...hat.com>, "Paul Moore" <paul@...l-moore.com>, "James
 Morris" <jmorris@...ei.org>, "Serge E. Hallyn" <serge@...lyn.com>, "Ard
 Biesheuvel" <ardb@...nel.org>, "Mario Limonciello"
 <mario.limonciello@....com>, <linux-kernel@...r.kernel.org>,
 <keyrings@...r.kernel.org>, <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH v2 2/3] tpm: Address !chip->auth in
 tpm_buf_append_name()

On Wed Jul 3, 2024 at 11:11 PM EEST, James Bottomley wrote:
> On Wed, 2024-07-03 at 21:24 +0300, Jarkko Sakkinen wrote:
> [...]
> > diff --git a/include/linux/tpm.h b/include/linux/tpm.h
> > index 21a67dc9efe8..2844fea4a12a 100644
> > --- a/include/linux/tpm.h
> > +++ b/include/linux/tpm.h
> > @@ -211,8 +211,8 @@ struct tpm_chip {
> >         u8 null_key_name[TPM2_NAME_SIZE];
> >         u8 null_ec_key_x[EC_PT_SZ];
> >         u8 null_ec_key_y[EC_PT_SZ];
> > -       struct tpm2_auth *auth;
> >  #endif
> > +       struct tpm2_auth *auth;
> >  };
>
> Since auth should only be present if CONFIG_TCG_TPM2_HMAC this is
> clearly an undesirable thing to do.  I think you did it because in a
> later patch you want to collapse the hmac sessions to use a single
> routine, but you can make that check with the preprocessor __and
> function defined in kconfig.h:
>
> if (__and(IS_ENABLED(CONFIG_TCG_TPM2_HMAC), chip->auth))
>
> Which will become 0 if the config is not enabled and chip->auth if it
> is, thus eliminating the code in the former case while not causing the
> compiler to complain about chip->auth not being defined even if it's
> under the config parameter.

I did not know about '__and()'. Thanks I'll use this!

>
> James

BR, Jarkko