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

[Kent Gibson <warthog618@gmail.com>]

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
>