drm/i915: Check for integer truncation on scatterlist creation

There is an impedance mismatch between the scatterlist API using unsigned
int and our memory/page accounting in unsigned long. That is we may try
to create a scatterlist for a large object that overflows returning a
small table into which we try to fit very many pages. As the object size
is under the control of userspace, we have to be prudent and catch the
conversion errors.

To catch the implicit truncation we check before calling scattterlist
creation Apis. we use overflows_type check and report E2BIG if the
overflows may raise. When caller does not return errno, use WARN_ON to
report a problem.

This is already used in our create ioctls to indicate if the uABI request
is simply too large for the backing store. Failing that type check,
we have a second check at sg_alloc_table time to make sure the values
we are passing into the scatterlist API are not truncated.

v2: Move added i915_utils's macro into drm_util header (Jani N)
v5: Fix macros to be enclosed in parentheses for complex values
Fix too long line warning
v8: Replace safe_conversion() with check_assign() (Kees)
v14: Remove shadowing macros of scatterlist creation api and fix to
explicitly overflow check where the scatterlist creation APIs are
called. (Jani)
v15: Add missing returning of error code when the WARN_ON() has been
detected. (Jani)

Cc: Tvrtko Ursulin <[e-mail]>
Cc: Brian Welty <[e-mail]>
Cc: Matthew Auld <[e-mail]>
Cc: Thomas Hellström <[e-mail]>
Signed-off-by: Chris Wilson <[e-mail]>
Co-developed-by: Gwan-gyeong Mun <[e-mail]>
Signed-off-by: Gwan-gyeong Mun <[e-mail]>
Reviewed-by: Nirmoy Das <[e-mail]>
Reviewed-by: Mauro Carvalho Chehab <[e-mail]>
Reviewed-by: Andrzej Hajda <[e-mail]>
Acked-by: Jani Nikula <[e-mail]>
Signed-off-by: Rodrigo Vivi <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/i915/gem/i915_gem_internal.c

···
 	struct drm_i915_private *i915 = to_i915(obj->base.dev);
 	struct sg_table *st;
 	struct scatterlist *sg;
-	unsigned int npages;
+	unsigned int npages; /* restricted by sg_alloc_table */
 	int max_order = MAX_ORDER;
 	unsigned int max_segment;
 	gfp_t gfp;
 
+	if (overflows_type(obj->base.size >> PAGE_SHIFT, npages))
+		return -E2BIG;
+
+	npages = obj->base.size >> PAGE_SHIFT;
 	max_segment = i915_sg_segment_size(i915->drm.dev) >> PAGE_SHIFT;
 	max_order = min(max_order, get_order(max_segment));
 
···
 	if (!st)
 		return -ENOMEM;
 
-	npages = obj->base.size / PAGE_SIZE;
 	if (sg_alloc_table(st, npages, GFP_KERNEL)) {
 		kfree(st);
 		return -ENOMEM;

drivers/gpu/drm/i915/gem/i915_gem_object.h

···
  * this and catch if we ever need to fix it. In the meantime, if you do
  * spot such a local variable, please consider fixing!
  *
- * Aside from our own locals (for which we have no excuse!):
- * - sg_table embeds unsigned int for nents
- *
  * We can check for invalidly typed locals with typecheck(), see for example
  * i915_gem_object_get_sg().
  */

drivers/gpu/drm/i915/gem/i915_gem_phys.c

···
 	void *dst;
 	int i;
 
+	/* Contiguous chunk, with a single scatterlist element */
+	if (overflows_type(obj->base.size, sg->length))
+		return -E2BIG;
+
 	if (GEM_WARN_ON(i915_gem_object_needs_bit17_swizzle(obj)))
 		return -EINVAL;
 

drivers/gpu/drm/i915/gem/i915_gem_shmem.c

···
 			 struct address_space *mapping,
 			 unsigned int max_segment)
 {
-	const unsigned long page_count = size / PAGE_SIZE;
+	unsigned int page_count; /* restricted by sg_alloc_table */
 	unsigned long i;
 	struct scatterlist *sg;
 	struct page *page;
···
 	gfp_t noreclaim;
 	int ret;
 
+	if (overflows_type(size / PAGE_SIZE, page_count))
+		return -E2BIG;
+
+	page_count = size / PAGE_SIZE;
 	/*
 	 * If there's no chance of allocating enough pages for the whole
 	 * object, bail early.
···
 	struct drm_i915_private *i915 = to_i915(obj->base.dev);
 	struct intel_memory_region *mem = obj->mm.region;
 	struct address_space *mapping = obj->base.filp->f_mapping;
-	const unsigned long page_count = obj->base.size / PAGE_SIZE;
 	unsigned int max_segment = i915_sg_segment_size(i915->drm.dev);
 	struct sg_table *st;
 	struct sgt_iter sgt_iter;
···
 		} else {
 			dev_warn(i915->drm.dev,
 				 "Failed to DMA remap %lu pages\n",
-				 page_count);
+				 obj->base.size >> PAGE_SHIFT);
 			goto err_pages;
 		}
 	}

drivers/gpu/drm/i915/gem/i915_gem_ttm.c

···
 	struct ttm_place requested, busy[I915_TTM_MAX_PLACEMENTS];
 	struct ttm_placement placement;
 
+	/* restricted by sg_alloc_table */
+	if (overflows_type(obj->base.size >> PAGE_SHIFT, unsigned int))
+		return -E2BIG;
+
 	GEM_BUG_ON(obj->mm.n_placements > I915_TTM_MAX_PLACEMENTS);
 
 	/* Move to the requested placement. */

drivers/gpu/drm/i915/gem/i915_gem_userptr.c

···
 
 static int i915_gem_userptr_get_pages(struct drm_i915_gem_object *obj)
 {
-	const unsigned long num_pages = obj->base.size >> PAGE_SHIFT;
 	unsigned int max_segment = i915_sg_segment_size(obj->base.dev->dev);
 	struct sg_table *st;
 	struct page **pvec;
+	unsigned int num_pages; /* limited by sg_alloc_table_from_pages_segment */
 	int ret;
 
+	if (overflows_type(obj->base.size >> PAGE_SHIFT, num_pages))
+		return -E2BIG;
+
+	num_pages = obj->base.size >> PAGE_SHIFT;
 	st = kmalloc(sizeof(*st), GFP_KERNEL);
 	if (!st)
 		return -ENOMEM;

drivers/gpu/drm/i915/gem/selftests/huge_gem_object.c

···
 {
 #define GFP (GFP_KERNEL | __GFP_NOWARN | __GFP_RETRY_MAYFAIL)
 	const unsigned long nreal = obj->scratch / PAGE_SIZE;
-	const unsigned long npages = obj->base.size / PAGE_SIZE;
+	unsigned int npages; /* restricted by sg_alloc_table */
 	struct scatterlist *sg, *src, *end;
 	struct sg_table *pages;
 	unsigned long n;
 
+	if (overflows_type(obj->base.size / PAGE_SIZE, npages))
+		return -E2BIG;
+
+	npages = obj->base.size / PAGE_SIZE;
 	pages = kmalloc(sizeof(*pages), GFP);
 	if (!pages)
 		return -ENOMEM;

drivers/gpu/drm/i915/gem/selftests/huge_pages.c

···
 	unsigned int sg_page_sizes;
 	u64 rem;
 
+	/* restricted by sg_alloc_table */
+	if (overflows_type(obj->base.size >> PAGE_SHIFT, unsigned int))
+		return -E2BIG;
+
 	st = kmalloc(sizeof(*st), GFP);
 	if (!st)
 		return -ENOMEM;
···
 	struct sg_table *st;
 	struct scatterlist *sg;
 	u64 rem;
+
+	/* restricted by sg_alloc_table */
+	if (overflows_type(obj->base.size >> PAGE_SHIFT, unsigned int))
+		return -E2BIG;
 
 	st = kmalloc(sizeof(*st), GFP);
 	if (!st)

drivers/gpu/drm/i915/gvt/dmabuf.c

···
 
 #define GEN8_DECODE_PTE(pte) (pte & GENMASK_ULL(63, 12))
 
-static int vgpu_gem_get_pages(
-		struct drm_i915_gem_object *obj)
+static int vgpu_gem_get_pages(struct drm_i915_gem_object *obj)
 {
 	struct drm_i915_private *dev_priv = to_i915(obj->base.dev);
 	struct intel_vgpu *vgpu;
···
 	int i, j, ret;
 	gen8_pte_t __iomem *gtt_entries;
 	struct intel_vgpu_fb_info *fb_info;
-	u32 page_num;
+	unsigned int page_num; /* limited by sg_alloc_table */
 
+	if (overflows_type(obj->base.size >> PAGE_SHIFT, page_num))
+		return -E2BIG;
+
+	page_num = obj->base.size >> PAGE_SHIFT;
 	fb_info = (struct intel_vgpu_fb_info *)obj->gvt_info;
 	if (drm_WARN_ON(&dev_priv->drm, !fb_info))
 		return -ENODEV;
···
 	if (unlikely(!st))
 		return -ENOMEM;
 
-	page_num = obj->base.size >> PAGE_SHIFT;
 	ret = sg_alloc_table(st, page_num, GFP_KERNEL);
 	if (ret) {
 		kfree(st);

drivers/gpu/drm/i915/i915_scatterlist.c

···
 
 	i915_refct_sgt_init(rsgt, node->size << PAGE_SHIFT);
 	st = &rsgt->table;
+	/* restricted by sg_alloc_table */
+	if (WARN_ON(overflows_type(DIV_ROUND_UP_ULL(node->size, segment_pages),
+				   unsigned int)))
+		return ERR_PTR(-E2BIG);
+
 	if (sg_alloc_table(st, DIV_ROUND_UP_ULL(node->size, segment_pages),
 			   GFP_KERNEL)) {
 		i915_refct_sgt_put(rsgt);
···
 
 	i915_refct_sgt_init(rsgt, size);
 	st = &rsgt->table;
+	/* restricted by sg_alloc_table */
+	if (WARN_ON(overflows_type(PFN_UP(res->size), unsigned int)))
+		return ERR_PTR(-E2BIG);
+
 	if (sg_alloc_table(st, PFN_UP(res->size), GFP_KERNEL)) {
 		i915_refct_sgt_put(rsgt);
 		return ERR_PTR(-ENOMEM);

drivers/gpu/drm/i915/selftests/i915_gem_gtt.c

···
 		return -ENOMEM;
 
 	rem = round_up(obj->base.size, BIT(31)) >> 31;
+	/* restricted by sg_alloc_table */
+	if (overflows_type(rem, unsigned int))
+		return -E2BIG;
+
 	if (sg_alloc_table(pages, rem, GFP)) {
 		kfree(pages);
 		return -ENOMEM;

drivers/gpu/drm/i915/selftests/scatterlist.c

···
 	struct scatterlist *sg;
 	unsigned long n, pfn;
 
+	/* restricted by sg_alloc_table */
+	if (overflows_type(max, unsigned int))
+		return -E2BIG;
+
 	if (sg_alloc_table(&pt->st, max,
 			   GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN))
 		return alloc_error;