[PATCH v2] drm/i915: Fix "mitigations" parsing if i915 is builtin

[PATCH v2] drm/i915: Fix "mitigations" parsing if i915 is builtin

[Jisheng Zhang]

I met below error during boot with i915 builtin if pass
"i915.mitigations=off":
[    0.015589] Booting kernel: `off' invalid for parameter `i915.mitigations'

The reason is slab subsystem isn't ready at that time, so kstrdup()
returns NULL. Fix this issue by using stack var instead of kstrdup().

Fixes: 984cadea032b ("drm/i915: Allow the sysadmin to override security mitigations")
Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
---
Since v1:
 - Ensure "str" is properly terminated. Thanks Ville for pointing this out.

 drivers/gpu/drm/i915/i915_mitigations.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_mitigations.c b/drivers/gpu/drm/i915/i915_mitigations.c
index 84f12598d145..231aad5ff46c 100644
--- a/drivers/gpu/drm/i915/i915_mitigations.c
+++ b/drivers/gpu/drm/i915/i915_mitigations.c
@@ -29,15 +29,14 @@ bool i915_mitigate_clear_residuals(void)
 static int mitigations_set(const char *val, const struct kernel_param *kp)
 {
 	unsigned long new = ~0UL;
-	char *str, *sep, *tok;
+	char str[64], *sep, *tok;
 	bool first = true;
 	int err = 0;
 
 	BUILD_BUG_ON(ARRAY_SIZE(names) >= BITS_PER_TYPE(mitigations));
 
-	str = kstrdup(val, GFP_KERNEL);
-	if (!str)
-		return -ENOMEM;
+	strncpy(str, val, sizeof(str) - 1);
+	str[sizeof(str) - 1] = '\0';
 
 	for (sep = str; (tok = strsep(&sep, ","));) {
 		bool enable = true;
@@ -86,7 +85,6 @@ static int mitigations_set(const char *val, const struct kernel_param *kp)
 			break;
 		}
 	}
-	kfree(str);
 	if (err)
 		return err;
 
-- 
2.31.0

Re: [PATCH v2] drm/i915: Fix "mitigations" parsing if i915 is builtin

[Ville Syrjälä]

On Wed, Apr 14, 2021 at 02:06:43PM +0800, Jisheng Zhang wrote:
> I met below error during boot with i915 builtin if pass
> "i915.mitigations=off":
> [    0.015589] Booting kernel: `off' invalid for parameter `i915.mitigations'
> 
> The reason is slab subsystem isn't ready at that time, so kstrdup()
> returns NULL. Fix this issue by using stack var instead of kstrdup().
> 
> Fixes: 984cadea032b ("drm/i915: Allow the sysadmin to override security mitigations")
> Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
> ---
> Since v1:
>  - Ensure "str" is properly terminated. Thanks Ville for pointing this out.
> 
>  drivers/gpu/drm/i915/i915_mitigations.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_mitigations.c b/drivers/gpu/drm/i915/i915_mitigations.c
> index 84f12598d145..231aad5ff46c 100644
> --- a/drivers/gpu/drm/i915/i915_mitigations.c
> +++ b/drivers/gpu/drm/i915/i915_mitigations.c
> @@ -29,15 +29,14 @@ bool i915_mitigate_clear_residuals(void)
>  static int mitigations_set(const char *val, const struct kernel_param *kp)
>  {
>  	unsigned long new = ~0UL;
> -	char *str, *sep, *tok;
> +	char str[64], *sep, *tok;
>  	bool first = true;
>  	int err = 0;
>  
>  	BUILD_BUG_ON(ARRAY_SIZE(names) >= BITS_PER_TYPE(mitigations));
>  
> -	str = kstrdup(val, GFP_KERNEL);
> -	if (!str)
> -		return -ENOMEM;
> +	strncpy(str, val, sizeof(str) - 1);
> +	str[sizeof(str) - 1] = '\0';

Looks correct, however strscpy() seems to be the thing we should
be using these days.

>  
>  	for (sep = str; (tok = strsep(&sep, ","));) {
>  		bool enable = true;
> @@ -86,7 +85,6 @@ static int mitigations_set(const char *val, const struct kernel_param *kp)
>  			break;
>  		}
>  	}
> -	kfree(str);
>  	if (err)
>  		return err;
>  
> -- 
> 2.31.0

-- 
Ville Syrjälä
Intel