Re: [PATCH 5/5] drm/i915: Use unsigned for overflow checks in execbuf

[Jani Nikula <jani.nikula@linux.intel.com>]

On Thu, 19 Sep 2013, Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
> There's actually no real risk since we already check for stricter
> constraints earlier (using UINT_MAX / sizeof (struct
> drm_i915_gem_exec_object2) as the limit). But in eb_create we use
> signed integers, which steals a factor of 2. Luckily struct
> drm_i915_gem_exec_object2 for this to not matter.

Parse error.

> Still, be consistent and use unsigned integers.
>
> Similar use unsinged integers when checking for overflows in the
> relocation entry processing.
>
> I've also added a new subtests to igt/gem_reloc_overflow to also
> test for overflowing args->buffer_count values.
>
> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> ---
>  drivers/gpu/drm/i915/i915_gem_execbuffer.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> index a733118..cd98aeb 100644
> --- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> +++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> @@ -45,18 +45,19 @@ struct eb_vmas {
>  static struct eb_vmas *
>  eb_create(struct drm_i915_gem_execbuffer2 *args, struct i915_address_space *vm)
>  {
> +	unsigned size, count;

My OCD says always use "unsigned int", not just "unsigned". To me this
is like having:

	const foo;
	static bar;

YMMV.

Otherwise,

Reviewed-by: Jani Nikula <jani.nikula@intel.com>


>  	struct eb_vmas *eb = NULL;
>  
>  	if (args->flags & I915_EXEC_HANDLE_LUT) {
> -		int size = args->buffer_count;
> +		size = args->buffer_count;
>  		size *= sizeof(struct i915_vma *);
>  		size += sizeof(struct eb_vmas);
>  		eb = kmalloc(size, GFP_TEMPORARY | __GFP_NOWARN | __GFP_NORETRY);
>  	}
>  
>  	if (eb == NULL) {
> -		int size = args->buffer_count;
> -		int count = PAGE_SIZE / sizeof(struct hlist_head) / 2;
> +		size = args->buffer_count;
> +		count = PAGE_SIZE / sizeof(struct hlist_head) / 2;
>  		BUILD_BUG_ON_NOT_POWER_OF_2(PAGE_SIZE / sizeof(struct hlist_head));
>  		while (count > 2*size)
>  			count >>= 1;
> @@ -667,7 +668,7 @@ i915_gem_execbuffer_relocate_slow(struct drm_device *dev,
>  	bool need_relocs;
>  	int *reloc_offset;
>  	int i, total, ret;
> -	int count = args->buffer_count;
> +	unsigned count = args->buffer_count;
>  
>  	if (WARN_ON(list_empty(&eb->vmas)))
>  		return 0;
> @@ -818,8 +819,8 @@ validate_exec_list(struct drm_i915_gem_exec_object2 *exec,
>  		   int count)
>  {
>  	int i;
> -	int relocs_total = 0;
> -	int relocs_max = INT_MAX / sizeof(struct drm_i915_gem_relocation_entry);
> +	unsigned relocs_total = 0;
> +	unsigned relocs_max = UINT_MAX / sizeof(struct drm_i915_gem_relocation_entry);
>  
>  	for (i = 0; i < count; i++) {
>  		char __user *ptr = to_user_ptr(exec[i].relocs_ptr);
> -- 
> 1.8.4.rc3
>
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-- 
Jani Nikula, Intel Open Source Technology Center