linux-kernel - Re: [PATCH v2] tpm: Opt-in in disable PCR integrity protection

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Message-ID: <10296fd8b0fcbf1d813577ef41738ffea12b70d1.camel@HansenPartnership.com>
Date: Thu, 07 Nov 2024 08:52:02 -0500
From: James Bottomley <James.Bottomley@...senPartnership.com>
To: Jarkko Sakkinen <jarkko@...nel.org>, linux-integrity@...r.kernel.org, 
 Jonathan Corbet <corbet@....net>, Peter Huewe <peterhuewe@....de>, Jason
 Gunthorpe <jgg@...pe.ca>
Cc: Roberto Sassu <roberto.sassu@...wei.com>, Mimi Zohar
 <zohar@...ux.ibm.com>,  linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] tpm: Opt-in in disable PCR integrity protection

On Thu, 2024-11-07 at 15:49 +0200, Jarkko Sakkinen wrote:
> On Thu Nov 7, 2024 at 3:20 PM EET, James Bottomley wrote:
> > On Thu, 2024-11-07 at 11:51 +0200, Jarkko Sakkinen wrote:
> > [...]
> > > +void tpm_buf_append_auth(struct tpm_chip *chip, struct tpm_buf
> > > *buf,
> > > +                        u8 attributes, u8 *passphrase, int
> > > passphrase_len)
> > > +{
> > > +       /* offset tells us where the sessions area begins */
> > > +       int offset = buf->handles * 4 + TPM_HEADER_SIZE;
> > > +       u32 len = 9 + passphrase_len;
> > > +
> > > +       if (tpm_buf_length(buf) != offset) {
> > > +               /* not the first session so update the existing
> > > length */
> > > +               len += get_unaligned_be32(&buf->data[offset]);
> > > +               put_unaligned_be32(len, &buf->data[offset]);
> > > +       } else {
> > > +               tpm_buf_append_u32(buf, len);
> > > +       }
> > > +       /* auth handle */
> > > +       tpm_buf_append_u32(buf, TPM2_RS_PW);
> > > +       /* nonce */
> > > +       tpm_buf_append_u16(buf, 0);
> > > +       /* attributes */
> > > +       tpm_buf_append_u8(buf, 0);
> > > +       /* passphrase */
> > > +       tpm_buf_append_u16(buf, passphrase_len);
> > > +       tpm_buf_append(buf, passphrase, passphrase_len);
> > > +}
> > > +
> > 
> > The rest of the code looks fine, but if you're going to extract
> > this as a separate function instead of doing the open coded struct
> > tpm2_null_auth that was there originally, you should probably
> > extract and use the tpm2_buf_append_auth() function in
> > trusted_tpm2.c
> 
> So this was straight up from Mimi's original patch :-)

Yes, I had the same comment prepped for that too.

> Hmm... was there duplicate use for this in the patch? I'll check
> this.

The original open coded the empty auth append with struct
tpm2_null_auth since it's the only user.  However, since we do have
another user in trusted keys, it might make sense to consolidate.

James