Re: [PATCH v2] tpm: introduce struct tpm_buf

[Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>]

On Mon, Jun 08, 2015 at 10:39:32PM +0200, Peter Hüwe wrote:
> Hi,
> 
> 
> Am Mittwoch, 3. Juni 2015, 18:39:14 schrieb Jarkko Sakkinen:
> > This patch introduces struct tpm_buf that provides a string buffer for
> > constructing TPM commands. This allows to construct variable sized TPM
> > commands. This feature is needed for TPM 2.0 commands in order to allow
> > policy authentication and algorithmic agility.
> > 
> > The commands in the tpm2-cmd.c have been updated to use struct tpm_buf.
> > Lots of awkward length calculations could be dropped because the buffer
> > knows its length.
> > 
> > The code is is along the lines of the string buffer code in
> > security/trusted/trusted.h.
> > 
> > Changes since v1:
> > 
> > - Fixed potential alignment issues in tpm_buf_tag().
> > 
> > Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
> 
> > +static inline void tpm_buf_append(struct tpm_buf *buf,
> > +				  const unsigned char *data,
> > +				  unsigned int len)
> > +{
> > +	struct tpm_input_header *head = (struct tpm_input_header *) buf->data;
> > +
> > +	BUG_ON((len + tpm_buf_length(buf)) > TPM_BUF_SIZE);
> > +
> > +	memcpy(&buf->data[tpm_buf_length(buf)], data, len);
> > +	head->length = cpu_to_be32(tpm_buf_length(buf) + len);
> > +}
> > +
> > +static inline void tpm_buf_store(struct tpm_buf *buf,
> > +				 unsigned int pos,
> > +				 const unsigned char *data,
> > +				 unsigned int len)
> > +{
> > +	BUG_ON((pos + len) > TPM_BUF_SIZE);
> > +
> > +	memcpy(&buf->data[pos], data, len);
> > +}
> 
> Don't you have to update the ->length here?

No. Store is for placing value in position, not appending to the end.

> Thanks,
> Peter

/Jarkko