cxl: core: Initialize eiw and eig to fix potential uninitialized use

[PATCH] cxl: core: Initialize eiw and eig to fix potential uninitialized use

Posted by Purva Yeshi 7 months, 4 weeks ago

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@gmail.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;
 	int high_pos, low_pos;
 
 	if (!test_bit(iw, &cxlhdm->iw_cap_mask))
-- 
2.34.1

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

Posted by Dan Williams 7 months, 3 weeks ago

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@gmail.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)) {

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

Posted by Alison Schofield 7 months ago

On Mon, Apr 21, 2025 at 10:39:38AM -0700, Dan Williams wrote:
> 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.
> > 

Hi Purva,

We'd like to see this patch revised and resubmitted. It is a
good cleanup!

Go ahead and send a v2 with Dan's suggestion as the solution.
There's a couple of options for the tags. Here I think it is
good to add this tag: 

Suggested-by: Dan Williams <dan.j.williams@intel.com>

followed by your Signed-off-by tag.


> > Signed-off-by: Purva Yeshi <purvayeshi550@gmail.com>
> > ---
You'll add a changelog in v2 here, below the ---,  something like:
Changes in v2:
- init eiw and eig in their helper functions (Dan)


Thanks,
Alison

> >  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)) {

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

Posted by Gregory Price 7 months, 3 weeks ago

On Sun, Apr 20, 2025 at 02:05:30AM +0530, 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@gmail.com>

Reviewed-by: Gregory Price <gourry@gourry.net>

> ---
>  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;
>  	int high_pos, low_pos;
>  
>  	if (!test_bit(iw, &cxlhdm->iw_cap_mask))
> -- 
> 2.34.1
>

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

Posted by Li Ming 7 months, 4 weeks ago

On 4/20/2025 4:35 AM, 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.

I also met them during checking cxl drivers code with code inspection tools. But they are not real issues, because both iw and ig are checked before calling check_interleave_cap(). That means check_interleave_cap() will always get a eiw and a eig correctly.

they are checked in cxl_port_setup_targets() in auto-assembly case, otherwise checked in interleave_ways_store() and interleave_guranularity_store().

I am not sure if we need this patch, let's see if other reviewers have more comments.


Ming

>
> Signed-off-by: Purva Yeshi <purvayeshi550@gmail.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;
>  	int high_pos, low_pos;
>  
>  	if (!test_bit(iw, &cxlhdm->iw_cap_mask))

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

Posted by Gregory Price 7 months, 3 weeks ago

On Sun, Apr 20, 2025 at 06:43:37PM +0800, Li Ming wrote:
> On 4/20/2025 4:35 AM, 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.
> 
> I also met them during checking cxl drivers code with code inspection tools. But they are not real issues, because both iw and ig are checked before calling check_interleave_cap(). That means check_interleave_cap() will always get a eiw and a eig correctly.
> 
> they are checked in cxl_port_setup_targets() in auto-assembly case, otherwise checked in interleave_ways_store() and interleave_guranularity_store().
>

unlikely, but things can change and if we know about this now we should
just fix it to avoid someone tripping over it in the future

~Gregory