Re: [PATCH v4 06/13] tpm: add buffer function to point to returned parameters

["Jarkko Sakkinen" <jarkko@kernel.org>]

On Tue May 2, 2023 at 5:09 PM EEST, Stefan Berger wrote:
>
>
> On 4/3/23 17:39, James Bottomley wrote:
> > Introducing encryption sessions changes where the return parameters

s/Introducing/Introduce/

Commit messages should always be in the imperative form.

> > are located in the buffer because if a return session is present
> > they're 4 bytes beyond the header with those 4 bytes showing the
> > parameter length.  If there is no return session, then they're in the
> > usual place immediately after the header.  The tpm_buf_parameters()
> > encapsulates this calculation and should be used everywhere
> > &buf.data[TPM_HEADER_SIZE] is used now.
> > 
> > Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
> > 
> > ---
> > v4: add kdoc
> > ---
> >   drivers/char/tpm/tpm-buf.c | 27 +++++++++++++++++++++++++++
> >   include/linux/tpm.h        |  2 ++
> >   2 files changed, 29 insertions(+)
> > 
> > diff --git a/drivers/char/tpm/tpm-buf.c b/drivers/char/tpm/tpm-buf.c
> > index da0f6e725c3f..d107321bcdff 100644
> > --- a/drivers/char/tpm/tpm-buf.c
> > +++ b/drivers/char/tpm/tpm-buf.c
> > @@ -277,3 +277,30 @@ u32 tpm_get_inc_u32(const u8 **ptr)
> >   	return val;
> >   }
> >   EXPORT_SYMBOL_GPL(tpm_get_inc_u32);
> > +
> > +static u16 tpm_buf_tag(struct tpm_buf *buf)
> > +{
> > +	struct tpm_header *head = (struct tpm_header *)buf->data;
> > +
> > +	return be16_to_cpu(head->tag);
> > +}
> > +
> > +/**
> > + * tpm_buf_parameters - return the parameters area of the tpm_buf
>
> in a TPM response
>
>
> > + * @buf: tpm_buf to use
> > + *
> > + * Where the parameters are located depends on the tag of a TPM
> > + * command. Evaluate this and return a pointer to the first byte of
> > + * the parameters area.
>
> I would also describe here what the non-obvious 4 bytes are that you are skipping over in case of TPM2_ST_SESSIONS.
>
> With this:
>
> Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
>
> > + *
> > + * @return: pointer to parameters area
> > + */
> > +u8 *tpm_buf_parameters(struct tpm_buf *buf)
> > +{
> > +	int offset = TPM_HEADER_SIZE;
> > +
> > +	if (tpm_buf_tag(buf) == TPM2_ST_SESSIONS)
> > +		offset += 4;
> > +
> > +	return &buf->data[offset];
> > +}
> > diff --git a/include/linux/tpm.h b/include/linux/tpm.h
> > index 845eadfed715..d2fea2afd37c 100644
> > --- a/include/linux/tpm.h
> > +++ b/include/linux/tpm.h
> > @@ -340,6 +340,8 @@ u8 tpm_get_inc_u8(const u8 **ptr);
> >   u16 tpm_get_inc_u16(const u8 **ptr);
> >   u32 tpm_get_inc_u32(const u8 **ptr);
> >   
> > +u8 *tpm_buf_parameters(struct tpm_buf *buf);
> > +
> >   /*
> >    * Check if TPM device is in the firmware upgrade mode.
> >    */

BR, Jarkko