linux-kernel - Re: [RFC PATCH 01/25] PCI: endpoint: pci-epf-vntb: Use array_index_nospec() on mws

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Message-ID: <iskqrcn6z2bnfnzrfc7kyy3x3ng7djn4ygral5cjtz3xiet4or@ktapppsfpzo7>
Date: Sat, 25 Oct 2025 01:24:29 +0900
From: Koichiro Den <den@...inux.co.jp>
To: Frank Li <Frank.li@....com>
Cc: ntb@...ts.linux.dev, linux-pci@...r.kernel.org, 
	dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org, mani@...nel.org, 
	kwilczynski@...nel.org, kishon@...nel.org, bhelgaas@...gle.com, corbet@....net, 
	vkoul@...nel.org, jdmason@...zu.us, dave.jiang@...el.com, allenbh@...il.com, 
	Basavaraj.Natikar@....com, Shyam-sundar.S-k@....com, kurt.schwemmer@...rosemi.com, 
	logang@...tatee.com, jingoohan1@...il.com, lpieralisi@...nel.org, robh@...nel.org, 
	jbrunet@...libre.com, fancer.lancer@...il.com, arnd@...db.de, pstanner@...hat.com, 
	elfring@...rs.sourceforge.net
Subject: Re: [RFC PATCH 01/25] PCI: endpoint: pci-epf-vntb: Use
 array_index_nospec() on mws_size[] access

On Thu, Oct 23, 2025 at 08:06:40PM -0400, Frank Li wrote:
> On Thu, Oct 23, 2025 at 04:18:52PM +0900, Koichiro Den wrote:
> > Follow common kernel idioms for indices derived from configfs attributes
> > and suppress Smatch warnings:
> >
> >   epf_ntb_mw1_show() warn: potential spectre issue 'ntb->mws_size' [r]
> >   epf_ntb_mw1_store() warn: potential spectre issue 'ntb->mws_size' [w]
> >
> > No functional changes.
> >
> > Signed-off-by: Koichiro Den <den@...inux.co.jp>
> > ---
> >  drivers/pci/endpoint/functions/pci-epf-vntb.c | 23 +++++++++++--------
> >  1 file changed, 14 insertions(+), 9 deletions(-)
> >
> > diff --git a/drivers/pci/endpoint/functions/pci-epf-vntb.c b/drivers/pci/endpoint/functions/pci-epf-vntb.c
> > index 83e9ab10f9c4..55307cd613c9 100644
> > --- a/drivers/pci/endpoint/functions/pci-epf-vntb.c
> > +++ b/drivers/pci/endpoint/functions/pci-epf-vntb.c
> > @@ -876,17 +876,19 @@ static ssize_t epf_ntb_##_name##_show(struct config_item *item,		\
> >  	struct config_group *group = to_config_group(item);		\
> >  	struct epf_ntb *ntb = to_epf_ntb(group);			\
> >  	struct device *dev = &ntb->epf->dev;				\
> > -	int win_no;							\
> > +	int win_no, idx;						\
> >  									\
> >  	if (sscanf(#_name, "mw%d", &win_no) != 1)			\
> >  		return -EINVAL;						\
> >  									\
> > -	if (win_no <= 0 || win_no > ntb->num_mws) {			\
> > -		dev_err(dev, "Invalid num_nws: %d value\n", ntb->num_mws); \
> > +	idx = win_no - 1;						\
> > +	if (idx < 0 || idx >= ntb->num_mws) {				\
> > +		dev_err(dev, "MW%d out of range (num_mws=%d)\n",	\
> > +			win_no, ntb->num_mws);				\
> >  		return -EINVAL;						\
> >  	}								\
> > -									\
> > -	return sprintf(page, "%lld\n", ntb->mws_size[win_no - 1]);	\
> > +	idx = array_index_nospec(idx, ntb->num_mws);			\
> > +	return sprintf(page, "%lld\n", ntb->mws_size[idx]);		\
> 
> keep original check if (win_no <= 0 || win_no > ntb->num_mws)
> 
> just
> 	idx = array_index_nospec(win_no - 1, ntb->num_mws);
> 	return sprintf(page, "%lld\n", ntb->mws_size[idx]);
> 
> It should be more simple.

Thanks for the review.

For minimal changes, that makes sense. I'd also like to update the dev_err
message (the "num_nws" typo, and I think what's invalid is win_no, not
num_mws). So how about combining your suggestion with the log message
update?

-Koichiro

> 
> Frank
> >  }
> >
> >  #define EPF_NTB_MW_W(_name)						\
> > @@ -896,7 +898,7 @@ static ssize_t epf_ntb_##_name##_store(struct config_item *item,	\
> >  	struct config_group *group = to_config_group(item);		\
> >  	struct epf_ntb *ntb = to_epf_ntb(group);			\
> >  	struct device *dev = &ntb->epf->dev;				\
> > -	int win_no;							\
> > +	int win_no, idx;						\
> >  	u64 val;							\
> >  	int ret;							\
> >  									\
> > @@ -907,12 +909,15 @@ static ssize_t epf_ntb_##_name##_store(struct config_item *item,	\
> >  	if (sscanf(#_name, "mw%d", &win_no) != 1)			\
> >  		return -EINVAL;						\
> >  									\
> > -	if (win_no <= 0 || win_no > ntb->num_mws) {			\
> > -		dev_err(dev, "Invalid num_nws: %d value\n", ntb->num_mws); \
> > +	idx = win_no - 1;						\
> > +	if (idx < 0 || idx >= ntb->num_mws) {				\
> > +		dev_err(dev, "MW%d out of range (num_mws=%d)\n",	\
> > +			win_no, ntb->num_mws);				\
> >  		return -EINVAL;						\
> >  	}								\
> >  									\
> > -	ntb->mws_size[win_no - 1] = val;				\
> > +	idx = array_index_nospec(idx, ntb->num_mws);			\
> > +	ntb->mws_size[idx] = val;					\
> >  									\
> >  	return len;							\
> >  }
> > --
> > 2.48.1
> >