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

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Message-ID: <aPrDEE80hSLbL57a@lizhi-Precision-Tower-5810>
Date: Thu, 23 Oct 2025 20:06:40 -0400
From: Frank Li <Frank.li@....com>
To: Koichiro Den <den@...inux.co.jp>
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 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.

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
>