2023-01-27 20:07:39

by Rob Clark

Subject: [PATCH] drm/i915: Fix potential bit_17 double-free

From: Rob Clark <[email protected]>

A userspace with multiple threads racing I915_GEM_SET_TILING to set the
tiling to I915_TILING_NONE could trigger a double free of the bit_17
bitmask. (Or conversely leak memory on the transition to tiled.) Move
allocation/free'ing of the bitmask within the section protected by the
obj lock.

Fixes: e9b73c67390a ("drm/i915: Reduce memory pressure during shrinker by preallocating swizzle pages")
Signed-off-by: Rob Clark <[email protected]>
---
drivers/gpu/drm/i915/gem/i915_gem_tiling.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_tiling.c b/drivers/gpu/drm/i915/gem/i915_gem_tiling.c
index fd42b89b7162..bc21b1c2350a 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_tiling.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_tiling.c
@@ -298,36 +298,37 @@ i915_gem_object_set_tiling(struct drm_i915_gem_object *obj,
vma->fence_alignment =
i915_gem_fence_alignment(i915,
vma->size, tiling, stride);

if (vma->fence)
vma->fence->dirty = true;
}
spin_unlock(&obj->vma.lock);

obj->tiling_and_stride = tiling | stride;
- i915_gem_object_unlock(obj);
-
- /* Force the fence to be reacquired for GTT access */
- i915_gem_object_release_mmap_gtt(obj);

/* Try to preallocate memory required to save swizzling on put-pages */
if (i915_gem_object_needs_bit17_swizzle(obj)) {
if (!obj->bit_17) {
obj->bit_17 = bitmap_zalloc(obj->base.size >> PAGE_SHIFT,
GFP_KERNEL);
}
} else {
bitmap_free(obj->bit_17);
obj->bit_17 = NULL;
}

+ i915_gem_object_unlock(obj);
+
+ /* Force the fence to be reacquired for GTT access */
+ i915_gem_object_release_mmap_gtt(obj);
+
return 0;
}

/**
* i915_gem_set_tiling_ioctl - IOCTL handler to set tiling mode
* @dev: DRM device
* @data: data pointer for the ioctl
* @file: DRM file for the ioctl call
*
* Sets the tiling mode of an object, returning the required swizzling of
--
2.38.1

2023-01-30 10:08:44

by Tvrtko Ursulin

Subject: Re: [PATCH] drm/i915: Fix potential bit_17 double-free

On 27/01/2023 20:05, Rob Clark wrote:
> From: Rob Clark <[email protected]>
>
> A userspace with multiple threads racing I915_GEM_SET_TILING to set the
> tiling to I915_TILING_NONE could trigger a double free of the bit_17
> bitmask. (Or conversely leak memory on the transition to tiled.) Move
> allocation/free'ing of the bitmask within the section protected by the
> obj lock.
>
> Fixes: e9b73c67390a ("drm/i915: Reduce memory pressure during shrinker by preallocating swizzle pages")

Should be:

Fixes: 2850748ef876 ("drm/i915: Pull i915_vma_pin under the vm->mutex")

Before that commit there as a "BKL" (struct_mutex) aroung the call to
i915_gem_object_set_tiling. Otherwise fix looks good:

Reviewed-by: Tvrtko Ursulin <[email protected]>

I'll tweak the fixes tag and merge in a minute, thanks for the fix!

Regards,

Tvrtko

> Signed-off-by: Rob Clark <[email protected]>
> ---
> drivers/gpu/drm/i915/gem/i915_gem_tiling.c | 9 +++++----
> 1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_tiling.c b/drivers/gpu/drm/i915/gem/i915_gem_tiling.c
> index fd42b89b7162..bc21b1c2350a 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_tiling.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_tiling.c
> @@ -298,36 +298,37 @@ i915_gem_object_set_tiling(struct drm_i915_gem_object *obj,
> vma->fence_alignment =
> i915_gem_fence_alignment(i915,
> vma->size, tiling, stride);
>
> if (vma->fence)
> vma->fence->dirty = true;
> }
> spin_unlock(&obj->vma.lock);
>
> obj->tiling_and_stride = tiling | stride;
> - i915_gem_object_unlock(obj);
> -
> - /* Force the fence to be reacquired for GTT access */
> - i915_gem_object_release_mmap_gtt(obj);
>
> /* Try to preallocate memory required to save swizzling on put-pages */
> if (i915_gem_object_needs_bit17_swizzle(obj)) {
> if (!obj->bit_17) {
> obj->bit_17 = bitmap_zalloc(obj->base.size >> PAGE_SHIFT,
> GFP_KERNEL);
> }
> } else {
> bitmap_free(obj->bit_17);
> obj->bit_17 = NULL;
> }
>
> + i915_gem_object_unlock(obj);
> +
> + /* Force the fence to be reacquired for GTT access */
> + i915_gem_object_release_mmap_gtt(obj);
> +
> return 0;
> }
>
> /**
> * i915_gem_set_tiling_ioctl - IOCTL handler to set tiling mode
> * @dev: DRM device
> * @data: data pointer for the ioctl
> * @file: DRM file for the ioctl call
> *
> * Sets the tiling mode of an object, returning the required swizzling of