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

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Message-Id: <D5FZT0QPHL0O.231WD6VUHC48X@kernel.org>
Date: Thu, 07 Nov 2024 15:49:14 +0200
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "James Bottomley" <James.Bottomley@...senPartnership.com>,
 <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 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 :-)

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

>
> James

BR, Jarkko