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

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Message-ID: <76d9ae11c339b589a8ec94f010e7439b7ce7d283.camel@HansenPartnership.com>
Date: Thu, 07 Nov 2024 08:20:53 -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 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

James