Re: [PATCH v8 2/3] tpm_crb_ffa:Introduce memzero macro to replace memset

[Jarkko Sakkinen <jarkko@kernel.org>]

On Fri, Jul 04, 2025 at 05:45:11AM +0300, Jarkko Sakkinen wrote:
> On Wed, Jul 02, 2025 at 10:58:56PM -0500, Prachotan Bathi wrote:
> > On 7/2/25 5:16 PM, Jarkko Sakkinen wrote:
> > 
> > > On Thu, Jun 26, 2025 at 01:45:20PM -0500, Prachotan Bathi wrote:
> > > > Add a memzero macro to simplify and standardize zeroing
> > > > FF-A data args, replacing direct uses of memset for
> > > > improved readability and maintainability.
> > > > 
> > > > Signed-off-by: Prachotan Bathi <prachotan.bathi@arm.com>
> > > > ---
> > > >   drivers/char/tpm/tpm_crb_ffa.c | 6 ++++--
> > > >   1 file changed, 4 insertions(+), 2 deletions(-)
> > > > 
> > > > diff --git a/drivers/char/tpm/tpm_crb_ffa.c b/drivers/char/tpm/tpm_crb_ffa.c
> > > > index 089d1e54bb46..397cc3b0a478 100644
> > > > --- a/drivers/char/tpm/tpm_crb_ffa.c
> > > > +++ b/drivers/char/tpm/tpm_crb_ffa.c
> > > > @@ -12,6 +12,8 @@
> > > >   #include <linux/arm_ffa.h>
> > > >   #include "tpm_crb_ffa.h"
> > > > +#define memzero(s, n) memset((s), 0, (n))
> > > > +
> > > >   /* TPM service function status codes */
> > > >   #define CRB_FFA_OK			0x05000001
> > > >   #define CRB_FFA_OK_RESULTS_RETURNED	0x05000002
> > > > @@ -192,7 +194,7 @@ static int __tpm_crb_ffa_send_receive(unsigned long func_id,
> > > >   	msg_ops = tpm_crb_ffa->ffa_dev->ops->msg_ops;
> > > >   	if (ffa_partition_supports_direct_req2_recv(tpm_crb_ffa->ffa_dev)) {
> > > > -		memset(&tpm_crb_ffa->direct_msg_data2, 0x00,
> > > > +		memzero(&tpm_crb_ffa->direct_msg_data2,
> > > >   		       sizeof(struct ffa_send_direct_data2));
> > > >   		tpm_crb_ffa->direct_msg_data2.data[0] = func_id;
> > > > @@ -205,7 +207,7 @@ static int __tpm_crb_ffa_send_receive(unsigned long func_id,
> > > >   		if (!ret)
> > > >   			ret = tpm_crb_ffa_to_linux_errno(tpm_crb_ffa->direct_msg_data2.data[0]);
> > > >   	} else {
> > > > -		memset(&tpm_crb_ffa->direct_msg_data, 0x00,
> > > > +		memzero(&tpm_crb_ffa->direct_msg_data,
> > > >   		       sizeof(struct ffa_send_direct_data));
> > > >   		tpm_crb_ffa->direct_msg_data.data1 = func_id;
> > > > -- 
> > > > 2.43.0
> > > > 
> > > It adds a ross-reference to the source code, meaning that you have to
> > > jump back and forth in the source code just to see that there is a
> > > function that wraps up a single memset() call.
> > > 
> > > How does that map to "readability"?
> > > 
> > > BR, Jarkko
> > 
> > Hi Jarkko
> > 
> > I've implemented this change post your feedback on v4 of the initial patch
> > series, maybe this should've been a question at that point, but what was the
> > reasoning for recommending that I use memzero instead? I'll use the same
> > reasoning to rephrase the commit message.
> 
> OK I found what you were referring to:
> 
> https://lore.kernel.org/linux-integrity/aFF-WNSolTdV9PZG@kernel.org/
> 
> Well, that was some truly misguided advice from my side so all the shame
> here is on me :-) There's no global memzero() and neither explicit
> version makes much sense here. Sorry about that.
> 
> I gave it now (actual) thought, and here's what I'd propose:
> 
> diff --git a/drivers/char/tpm/tpm_crb_ffa.c b/drivers/char/tpm/tpm_crb_ffa.c
> index 96746d5b03e3..e769f6143a7c 100644
> --- a/drivers/char/tpm/tpm_crb_ffa.c
> +++ b/drivers/char/tpm/tpm_crb_ffa.c
> @@ -203,26 +203,20 @@ static int __tpm_crb_ffa_try_send_receive(unsigned long func_id,
>  	msg_ops = tpm_crb_ffa->ffa_dev->ops->msg_ops;
>  
>  	if (ffa_partition_supports_direct_req2_recv(tpm_crb_ffa->ffa_dev)) {
> -		memzero(&tpm_crb_ffa->direct_msg_data2,
> -		       sizeof(struct ffa_send_direct_data2));
> -
> -		tpm_crb_ffa->direct_msg_data2.data[0] = func_id;
> -		tpm_crb_ffa->direct_msg_data2.data[1] = a0;
> -		tpm_crb_ffa->direct_msg_data2.data[2] = a1;
> -		tpm_crb_ffa->direct_msg_data2.data[3] = a2;
> +		tpm_crb_ffa->direct_msg_data2 = (struct ffa_send_direct_data2){
> +			.data = { func_id, a0, a1, a2 },
> +		};
>  
>  		ret = msg_ops->sync_send_receive2(tpm_crb_ffa->ffa_dev,
>  				&tpm_crb_ffa->direct_msg_data2);
>  		if (!ret)
>  			ret = tpm_crb_ffa_to_linux_errno(tpm_crb_ffa->direct_msg_data2.data[0]);
>  	} else {
> -		memzero(&tpm_crb_ffa->direct_msg_data,
> -		       sizeof(struct ffa_send_direct_data));
> -
> -		tpm_crb_ffa->direct_msg_data.data1 = func_id;
> -		tpm_crb_ffa->direct_msg_data.data2 = a0;
> -		tpm_crb_ffa->direct_msg_data.data3 = a1;
> -		tpm_crb_ffa->direct_msg_data.data4 = a2;
> +		tpm_crb_ffa->direct_msg_data = (struct ffa_send_direct_data){
> +			.data1 = func_id,
> +			.data2 = a0,
> +			.data3 = a1,

Oops, lacks a2 but you probably get the idea :-)

BR, Jarkko