[PATCH v3] gpio: prevent potential speculation leaks in gpio_device_get_desc()

[PATCH v3] gpio: prevent potential speculation leaks in gpio_device_get_desc()

[Hagar Hemdan]

Userspace may trigger a speculative read of an address outside the gpio
descriptor array.
Users can do that by calling gpio_ioctl() with an offset out of range.
Offset is copied from user and then used as an array index to get
the gpio descriptor without sanitization in gpio_device_get_desc().

This change ensures that the offset is sanitized by using
array_index_nospec() to mitigate any possibility of speculative
information leaks.

This bug was discovered and resolved using Coverity Static Analysis
Security Testing (SAST) by Synopsys, Inc.

Fixes: aad955842d1c ("gpiolib: cdev: support GPIO_V2_GET_LINEINFO_IOCTL and GPIO_V2_GET_LINEINFO_WATCH_IOCTL")
Signed-off-by: Hagar Hemdan <hagarhem@amazon.com>
---
v3: update the commit mesg
---
 drivers/gpio/gpiolib.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index fa50db0c3605..b58e4fe78cec 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -17,6 +17,7 @@
 #include <linux/list.h>
 #include <linux/lockdep.h>
 #include <linux/module.h>
+#include <linux/nospec.h>
 #include <linux/of.h>
 #include <linux/pinctrl/consumer.h>
 #include <linux/seq_file.h>
@@ -201,7 +202,7 @@ gpio_device_get_desc(struct gpio_device *gdev, unsigned int hwnum)
 	if (hwnum >= gdev->ngpio)
 		return ERR_PTR(-EINVAL);
 
-	return &gdev->descs[hwnum];
+	return &gdev->descs[array_index_nospec(hwnum, gdev->ngpio)];
 }
 EXPORT_SYMBOL_GPL(gpio_device_get_desc);
 
-- 
2.40.1

Re: [PATCH v3] gpio: prevent potential speculation leaks in gpio_device_get_desc()

[Kent Gibson]

On Fri, May 17, 2024 at 10:12:27AM +0000, Hagar Hemdan wrote:
> Userspace may trigger a speculative read of an address outside the gpio
> descriptor array.
> Users can do that by calling gpio_ioctl() with an offset out of range.
> Offset is copied from user and then used as an array index to get
> the gpio descriptor without sanitization in gpio_device_get_desc().
>
> This change ensures that the offset is sanitized by using
> array_index_nospec() to mitigate any possibility of speculative
> information leaks.
>
> This bug was discovered and resolved using Coverity Static Analysis
> Security Testing (SAST) by Synopsys, Inc.
>
> Fixes: aad955842d1c ("gpiolib: cdev: support GPIO_V2_GET_LINEINFO_IOCTL and GPIO_V2_GET_LINEINFO_WATCH_IOCTL")

I still don't think this Fixes commit is right, and that would impact
where this gets backported to, but Bart can weigh in on that.

Cheers,
Kent.


> Signed-off-by: Hagar Hemdan <hagarhem@amazon.com>
> ---
> v3: update the commit mesg
> ---
>  drivers/gpio/gpiolib.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index fa50db0c3605..b58e4fe78cec 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -17,6 +17,7 @@
>  #include <linux/list.h>
>  #include <linux/lockdep.h>
>  #include <linux/module.h>
> +#include <linux/nospec.h>
>  #include <linux/of.h>
>  #include <linux/pinctrl/consumer.h>
>  #include <linux/seq_file.h>
> @@ -201,7 +202,7 @@ gpio_device_get_desc(struct gpio_device *gdev, unsigned int hwnum)
>  	if (hwnum >= gdev->ngpio)
>  		return ERR_PTR(-EINVAL);
>
> -	return &gdev->descs[hwnum];
> +	return &gdev->descs[array_index_nospec(hwnum, gdev->ngpio)];
>  }
>  EXPORT_SYMBOL_GPL(gpio_device_get_desc);
>
> --
> 2.40.1
>

Re: [PATCH v3] gpio: prevent potential speculation leaks in gpio_device_get_desc()

[Hagar Hemdan]

On Fri, May 17, 2024 at 08:49:11PM +0800, Kent Gibson wrote:
> On Fri, May 17, 2024 at 10:12:27AM +0000, Hagar Hemdan wrote:
> > Userspace may trigger a speculative read of an address outside the gpio
> > descriptor array.
> > Users can do that by calling gpio_ioctl() with an offset out of range.
> > Offset is copied from user and then used as an array index to get
> > the gpio descriptor without sanitization in gpio_device_get_desc().
> >
> > This change ensures that the offset is sanitized by using
> > array_index_nospec() to mitigate any possibility of speculative
> > information leaks.
> >
> > This bug was discovered and resolved using Coverity Static Analysis
> > Security Testing (SAST) by Synopsys, Inc.
> >
> > Fixes: aad955842d1c ("gpiolib: cdev: support GPIO_V2_GET_LINEINFO_IOCTL and GPIO_V2_GET_LINEINFO_WATCH_IOCTL")
> 
> I still don't think this Fixes commit is right, and that would impact
> where this gets backported to, but Bart can weigh in on that.
> 
> Cheers,
> Kent.
>
yes, this Fixes commit is wrong. Stable trees need another fix patch.
I will remove this Fixes commit in the next revision.

Thanks,
Hagar
> 
> > Signed-off-by: Hagar Hemdan <hagarhem@amazon.com>
> > ---
> > v3: update the commit mesg
> > ---
> >  drivers/gpio/gpiolib.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> > index fa50db0c3605..b58e4fe78cec 100644
> > --- a/drivers/gpio/gpiolib.c
> > +++ b/drivers/gpio/gpiolib.c
> > @@ -17,6 +17,7 @@
> >  #include <linux/list.h>
> >  #include <linux/lockdep.h>
> >  #include <linux/module.h>
> > +#include <linux/nospec.h>
> >  #include <linux/of.h>
> >  #include <linux/pinctrl/consumer.h>
> >  #include <linux/seq_file.h>
> > @@ -201,7 +202,7 @@ gpio_device_get_desc(struct gpio_device *gdev, unsigned int hwnum)
> >  	if (hwnum >= gdev->ngpio)
> >  		return ERR_PTR(-EINVAL);
> >
> > -	return &gdev->descs[hwnum];
> > +	return &gdev->descs[array_index_nospec(hwnum, gdev->ngpio)];
> >  }
> >  EXPORT_SYMBOL_GPL(gpio_device_get_desc);
> >
> > --
> > 2.40.1
> >