Re: [PATCH v2 2/7] drm/i915/gem: Typecheck page lookups

Gwan-gyeong Mun <gwan-gyeong.mun@xxxxxxxxx> · Tue, 12 Jul 2022 13:29:55 +0300

On 7/6/22 8:10 PM, Mauro Carvalho Chehab wrote:
On Wed, 6 Jul 2022 19:33:22 +0300
Gwan-gyeong Mun <gwan-gyeong.mun@xxxxxxxxx> wrote:

On 7/5/22 5:35 PM, Mauro Carvalho Chehab wrote:
On Tue,  5 Jul 2022 15:24:50 +0300
Gwan-gyeong Mun <gwan-gyeong.mun@xxxxxxxxx> wrote:
   
From: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>

We need to check that we avoid integer overflows when looking up a page,
and so fix all the instances where we have mistakenly used a plain
integer instead of a more suitable long. Be pedantic and add integer
typechecking to the lookup so that we can be sure that we are safe.
And it also uses pgoff_t as our page lookups must remain compatible with
the page cache, pgoff_t is currently exactly unsigned long.

v2: Move added i915_utils's macro into drm_util header (Jani N)

Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun@xxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>
Cc: Matthew Auld <matthew.auld@xxxxxxxxx>
Cc: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
Reviewed-by: Nirmoy Das <nirmoy.das@xxxxxxxxx>
---
   drivers/gpu/drm/i915/gem/i915_gem_object.c    |  7 +-
   drivers/gpu/drm/i915/gem/i915_gem_object.h    | 67 ++++++++++++++-----
   drivers/gpu/drm/i915/gem/i915_gem_pages.c     | 25 ++++---
   drivers/gpu/drm/i915/gem/i915_gem_ttm.c       |  2 +-
   .../drm/i915/gem/selftests/i915_gem_context.c | 12 ++--
   .../drm/i915/gem/selftests/i915_gem_mman.c    |  8 +--
   .../drm/i915/gem/selftests/i915_gem_object.c  |  8 +--
   drivers/gpu/drm/i915/i915_gem.c               | 18 +++--
   drivers/gpu/drm/i915/i915_vma.c               |  8 +--
   9 files changed, 100 insertions(+), 55 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.c b/drivers/gpu/drm/i915/gem/i915_gem_object.c
index ccec4055fde3..90996fe8ad45 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_object.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c
@@ -421,10 +421,11 @@ void __i915_gem_object_invalidate_frontbuffer(struct drm_i915_gem_object *obj,
   static void
   i915_gem_object_read_from_page_kmap(struct drm_i915_gem_object *obj, u64 offset, void *dst, int size)
   {
+	pgoff_t idx = offset >> PAGE_SHIFT;
   	void *src_map;
   	void *src_ptr;
   
-	src_map = kmap_atomic(i915_gem_object_get_page(obj, offset >> PAGE_SHIFT));
+	src_map = kmap_atomic(i915_gem_object_get_page(obj, idx));
   
   	src_ptr = src_map + offset_in_page(offset);
   	if (!(obj->cache_coherent & I915_BO_CACHE_COHERENT_FOR_READ))
@@ -437,9 +438,10 @@ i915_gem_object_read_from_page_kmap(struct drm_i915_gem_object *obj, u64 offset,
   static void
   i915_gem_object_read_from_page_iomap(struct drm_i915_gem_object *obj, u64 offset, void *dst, int size)
   {
+	pgoff_t idx = offset >> PAGE_SHIFT;
+	dma_addr_t dma = i915_gem_object_get_dma_address(obj, idx);
   	void __iomem *src_map;
   	void __iomem *src_ptr;
-	dma_addr_t dma = i915_gem_object_get_dma_address(obj, offset >> PAGE_SHIFT);
   
   	src_map = io_mapping_map_wc(&obj->mm.region->iomap,
   				    dma - obj->mm.region->region.start,
@@ -468,6 +470,7 @@ i915_gem_object_read_from_page_iomap(struct drm_i915_gem_object *obj, u64 offset
    */
   int i915_gem_object_read_from_page(struct drm_i915_gem_object *obj, u64 offset, void *dst, int size)
   {
+	GEM_BUG_ON(overflows_type(offset >> PAGE_SHIFT, pgoff_t));
   	GEM_BUG_ON(offset >= obj->base.size);
   	GEM_BUG_ON(offset_in_page(offset) > PAGE_SIZE - size);
   	GEM_BUG_ON(!i915_gem_object_has_pinned_pages(obj));
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.h b/drivers/gpu/drm/i915/gem/i915_gem_object.h
index 6f0a3ce35567..a60c6f4517d5 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_object.h
+++ b/drivers/gpu/drm/i915/gem/i915_gem_object.h
@@ -27,8 +27,10 @@ enum intel_region_id;
    * 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 num_pages
- * - get_user_pages*() mixed ints with longs
+ * - sg_table embeds unsigned int for nents
+ *
+ * We can check for invalidly typed locals with typecheck(), see for example
+ * i915_gem_object_get_sg().
    */
   #define GEM_CHECK_SIZE_OVERFLOW(sz) \
   	GEM_WARN_ON((sz) >> PAGE_SHIFT > INT_MAX)
@@ -366,41 +368,70 @@ int i915_gem_object_set_tiling(struct drm_i915_gem_object *obj,
   struct scatterlist *
   __i915_gem_object_get_sg(struct drm_i915_gem_object *obj,
   			 struct i915_gem_object_page_iter *iter,
-			 unsigned int n,
-			 unsigned int *offset, bool dma);
+			 pgoff_t  n,
+			 unsigned int *offset);
+
+#define __i915_gem_object_get_sg(obj, it, n, offset) ({ \
+	exactly_pgoff_t(n); \
+	(__i915_gem_object_get_sg)(obj, it, n, offset); \
+})
   
   static inline struct scatterlist *
-i915_gem_object_get_sg(struct drm_i915_gem_object *obj,
-		       unsigned int n,
+i915_gem_object_get_sg(struct drm_i915_gem_object *obj, pgoff_t n,
   		       unsigned int *offset)
   {
-	return __i915_gem_object_get_sg(obj, &obj->mm.get_page, n, offset, false);
+	return __i915_gem_object_get_sg(obj, &obj->mm.get_page, n, offset);
   }
   
+#define i915_gem_object_get_sg(obj, n, offset) ({ \
+	exactly_pgoff_t(n); \
+	(i915_gem_object_get_sg)(obj, n, offset); \
+})
+
   static inline struct scatterlist *
-i915_gem_object_get_sg_dma(struct drm_i915_gem_object *obj,
-			   unsigned int n,
+i915_gem_object_get_sg_dma(struct drm_i915_gem_object *obj, pgoff_t n,
   			   unsigned int *offset)
   {
-	return __i915_gem_object_get_sg(obj, &obj->mm.get_dma_page, n, offset, true);
+	return __i915_gem_object_get_sg(obj, &obj->mm.get_dma_page, n, offset);
   }
   
+#define i915_gem_object_get_sg_dma(obj, n, offset) ({ \
+	exactly_pgoff_t(n); \
+	(i915_gem_object_get_sg_dma)(obj, n, offset); \
+})
+
   struct page *
-i915_gem_object_get_page(struct drm_i915_gem_object *obj,
-			 unsigned int n);
+i915_gem_object_get_page(struct drm_i915_gem_object *obj, pgoff_t n);
+
+#define i915_gem_object_get_page(obj, n) ({ \
+	exactly_pgoff_t(n); \
+	(i915_gem_object_get_page)(obj, n); \
+})
   
   struct page *
-i915_gem_object_get_dirty_page(struct drm_i915_gem_object *obj,
-			       unsigned int n);
+i915_gem_object_get_dirty_page(struct drm_i915_gem_object *obj, pgoff_t n);
+
+#define i915_gem_object_get_dirty_page(obj, n) ({ \
+	exactly_pgoff_t(n); \
+	(i915_gem_object_get_dirty_page)(obj, n); \
+})
   
   dma_addr_t
-i915_gem_object_get_dma_address_len(struct drm_i915_gem_object *obj,
-				    unsigned long n,
+i915_gem_object_get_dma_address_len(struct drm_i915_gem_object *obj, pgoff_t n,
   				    unsigned int *len);
   
+#define i915_gem_object_get_dma_address_len(obj, n, len) ({ \
+	exactly_pgoff_t(n); \
+	(i915_gem_object_get_dma_address_len)(obj, n, len); \
+})
+
   dma_addr_t
-i915_gem_object_get_dma_address(struct drm_i915_gem_object *obj,
-				unsigned long n);
+i915_gem_object_get_dma_address(struct drm_i915_gem_object *obj, pgoff_t n);
+
+#define i915_gem_object_get_dma_address(obj, n) ({ \
+	exactly_pgoff_t(n); \
+	(i915_gem_object_get_dma_address)(obj, n); \
+})
   
   void __i915_gem_object_set_pages(struct drm_i915_gem_object *obj,
   				 struct sg_table *pages,
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_pages.c b/drivers/gpu/drm/i915/gem/i915_gem_pages.c
index 97c820eee115..1d1edcb3514b 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_pages.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_pages.c
@@ -503,14 +503,16 @@ void __i915_gem_object_release_map(struct drm_i915_gem_object *obj)
   }
   
   struct scatterlist *
-__i915_gem_object_get_sg(struct drm_i915_gem_object *obj,
+(__i915_gem_object_get_sg)(struct drm_i915_gem_object *obj,
   			 struct i915_gem_object_page_iter *iter,
-			 unsigned int n,
-			 unsigned int *offset,
-			 bool dma)
+			 pgoff_t n,
+			 unsigned int *offset)
+

Nitpick: no need to place the function name in parenthesis.
   
   {
-	struct scatterlist *sg;
+	const bool dma = iter == &obj->mm.get_dma_page ||
+			 iter == &obj->ttm.get_io_page;
   	unsigned int idx, count;
+	struct scatterlist *sg;
   
   	might_sleep();
   	GEM_BUG_ON(n >= obj->base.size >> PAGE_SHIFT);
@@ -618,7 +620,7 @@ __i915_gem_object_get_sg(struct drm_i915_gem_object *obj,
   }
   
   struct page *
-i915_gem_object_get_page(struct drm_i915_gem_object *obj, unsigned int n)
+(i915_gem_object_get_page)(struct drm_i915_gem_object *obj, pgoff_t n)

Same as above: why are you placing parenthesis at the function name here?
Just use:
	
	struct page *
	i915_gem_object_get_page(struct drm_i915_gem_object *obj, pgoff_t n)
  
In this case, the macro and function have the same name. If parenthesis
is not used, the following compile error occurs as the macro is applied
to the c code.

./drivers/gpu/drm/i915/gem/i915_gem_object.h:356:55: error: expected
identifier or ‘(’ before ‘{’ token
    356 | #define __i915_gem_object_get_sg(obj, it, n, offset) ({ \
        |                                                       ^
drivers/gpu/drm/i915/gem/i915_gem_pages.c:506:1: note: in expansion of
macro ‘__i915_gem_object_get_sg’
    506 | __i915_gem_object_get_sg(struct drm_i915_gem_object *obj,
        | ^~~~~~~~~~~~~~~~~~~~~~~~

And all of the parts you leave comments below are cases where the names
of macros and functions are the same.

Don't use the same macro name on a function. This is very confusing
and will prevent ever adding documentation for it, as, for kernel-doc,
macros and functions are handled at the same namespace. So, no
duplication is allowed.

Probably the best here would be to replace the macros by inlined
functions.

When using an inline function, the function can check the types after 
typecasting its arguments.
It is more efficient to use the above macro style to check input 
argument's type in the compilation stage.
This way is also used in the macro below among the existing i915 codes.

#define sg_alloc_table(sgt, nents, gfp) \
	overflows_type(nents, __sg_size_t) ? -E2BIG : (sg_alloc_table)(sgt, 
(__sg_size_t)(nents), gfp)

#define sg_alloc_table_from_pages_segment(sgt, pages, npages, offset, 
size, max_segment, gfp) \
	overflows_type(npages, __sg_size_t) ? -E2BIG : 
(sg_alloc_table_from_pages_segment)(sgt, pages, (__sg_size_t)(npages), 
offset, size, max_segment, gfp)


This method has the advantage of being able to check the type of a 
variable passed as a function argument before it is typecast.

However, the kernel-doc's issues is something I didn't think consider 
before. To fix the naming problem in the documentation, I will change 
the macro name and the function name differently and send it as a new 
version.

Br,
G.G.
Regards,
Mauro







