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

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Date:   Thu, 15 Apr 2021 18:50:37 +0300
From:   Ville Syrjälä <ville.syrjala@...ux.intel.com>
To:     Jisheng Zhang <Jisheng.Zhang@...aptics.com>
Cc:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Jon Bloomfield <jon.bloomfield@...el.com>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] drm/i915: Fix "mitigations" parsing if i915 is builtin

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@...aptics.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