linux-kernel - Re: [PATCH] cxl: core: Initialize eiw and eig to fix potential uninitialized use

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Message-ID: <680682dabbd09_71fe29462@dwillia2-xfh.jf.intel.com.notmuch>
Date: Mon, 21 Apr 2025 10:39:38 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Purva Yeshi <purvayeshi550@...il.com>, <dave@...olabs.net>,
	<jonathan.cameron@...wei.com>, <dave.jiang@...el.com>,
	<alison.schofield@...el.com>, <vishal.l.verma@...el.com>,
	<ira.weiny@...el.com>, <dan.j.williams@...el.com>
CC: <ming.li@...omail.com>, <huang.ying.caritas@...il.com>,
	<linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>, Purva Yeshi
	<purvayeshi550@...il.com>
Subject: Re: [PATCH] cxl: core: Initialize eiw and eig to fix potential
 uninitialized use

Purva Yeshi wrote:
> Fix Smatch-detected issue:
> 
> drivers/cxl/core/region.c:1292 check_interleave_cap()
> error: uninitialized symbol 'eiw'.
> drivers/cxl/core/region.c:1297 check_interleave_cap()
> error: uninitialized symbol 'eig'.
> drivers/cxl/core/region.c:1299 check_interleave_cap()
> error: uninitialized symbol 'eig'.
> 
> Smatch reports possible uninitialized usage of these variables if
> the helper functions ways_to_eiw() or granularity_to_eig() fail to
> assign values under certain conditions.
> 
> Initialize the eiw and eig variables to zero when they are declared
> in check_interleave_cap() to prevent potential use of uninitialized
> values.
> 
> Signed-off-by: Purva Yeshi <purvayeshi550@...il.com>
> ---
>  drivers/cxl/core/region.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index c3f4dc244df7..edf8636f190a 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -1266,8 +1266,8 @@ static int check_interleave_cap(struct cxl_decoder *cxld, int iw, int ig)
>  	struct cxl_port *port = to_cxl_port(cxld->dev.parent);
>  	struct cxl_hdm *cxlhdm = dev_get_drvdata(&port->dev);
>  	unsigned int interleave_mask;
> -	u8 eiw;
> -	u16 eig;
> +	u8 eiw = 0;
> +	u16 eig = 0;

I appreciate that this quiets the warning, but it is leaving a trip
hazard for future code refactoring. I would prefer to make this scenario
harder to repeat in the future with something like:

diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
index be8a7dc77719..5f20919207ae 100644
--- a/drivers/cxl/cxl.h
+++ b/drivers/cxl/cxl.h
@@ -107,6 +107,7 @@ static inline int eiw_to_ways(u8 eiw, unsigned int *ways)
 
 static inline int granularity_to_eig(int granularity, u16 *eig)
 {
+	*eig = 0;
 	if (granularity > SZ_16K || granularity < CXL_DECODER_MIN_GRANULARITY ||
 	    !is_power_of_2(granularity))
 		return -EINVAL;
@@ -116,6 +117,7 @@ static inline int granularity_to_eig(int granularity, u16 *eig)
 
 static inline int ways_to_eiw(unsigned int ways, u8 *eiw)
 {
+	*eiw = 0;
 	if (ways > 16)
 		return -EINVAL;
 	if (is_power_of_2(ways)) {