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

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Message-ID: <20250704114010.0d210c31@pumpkin>
Date: Fri, 4 Jul 2025 11:40:10 +0100
From: David Laight <david.laight.linux@...il.com>
To: Jarkko Sakkinen <jarkko@...nel.org>
Cc: Prachotan Bathi <prachotan.bathi@....com>, Peter Huewe
 <peterhuewe@....de>, Jason Gunthorpe <jgg@...pe.ca>, Stuart Yoder
 <stuart.yoder@....com>, linux-integrity@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 2/3] tpm_crb_ffa:Introduce memzero macro to replace
 memset

On Fri, 4 Jul 2025 05:56:50 +0300
Jarkko Sakkinen <jarkko@...nel.org> wrote:

> On Fri, Jul 04, 2025 at 05:45:11AM +0300, Jarkko Sakkinen wrote:
...
> > 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 },
> > +		};

clang has a habit of compiling that as an un-named on-stack structure that
is initialised and then memcpy() used to copy it into place.
Often not was intended and blows the stack when the structure is large.

So probably not a pattern that should be encouraged.

	David