Re: [PATCH] hwmon: (nct6775) Fix potential Spectre v1

[Guenter Roeck]

On Wed, Aug 15, 2018 at 08:14:37AM -0500, Gustavo A. R. Silva wrote:
> val can be indirectly controlled by user-space, hence leading to
> a potential exploitation of the Spectre variant 1 vulnerability.
> 
> This issue was detected with the help of Smatch:
> 
> vers/hwmon/nct6775.c:2698 store_pwm_weight_temp_sel() warn: potential
> spectre issue 'data->temp_src' [r]
> 
> Fix this by sanitizing val before using it to index data->temp_src
> 
> Notice that given that speculation windows are large, the policy is
> to kill the speculation on the first load and not worry if it can be
> completed with a dependent load/store [1].
> 
> [1] https://marc.info/?l=linux-kernel&m=152449131114778&w=2
> 
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>

Applied.

Thanks,
Guenter

> ---
>  drivers/hwmon/nct6775.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/hwmon/nct6775.c b/drivers/hwmon/nct6775.c
> index c6bd61e..944f5b6 100644
> --- a/drivers/hwmon/nct6775.c
> +++ b/drivers/hwmon/nct6775.c
> @@ -63,6 +63,7 @@
>  #include <linux/bitops.h>
>  #include <linux/dmi.h>
>  #include <linux/io.h>
> +#include <linux/nospec.h>
>  #include "lm75.h"
>  
>  #define USE_ALTERNATE
> @@ -2689,6 +2690,7 @@ store_pwm_weight_temp_sel(struct device *dev, struct device_attribute *attr,
>  		return err;
>  	if (val > NUM_TEMP)
>  		return -EINVAL;
> +	val = array_index_nospec(val, NUM_TEMP + 1);
>  	if (val && (!(data->have_temp & BIT(val - 1)) ||
>  		    !data->temp_src[val - 1]))
>  		return -EINVAL;
> -- 
> 2.7.4
>