[Intel-gfx] [PATCH] drm/i915: Fix vmap_batch page iterator overrun

[Mika Kuoppala]

vmap_batch() calculates amount of needed pages for the mapping
we are going to create. And it uses this page count as an
argument for the for_each_sg_pages() macro. The macro takes the number
of sg list entities as an argument, not the page count. So we ended
up iterating through all the pages on the mapped object, corrupting
memory past the smaller pages[] array.

Fix this by bailing out when we have enough pages.

Cc: Chris Wilson <chris at chris-wilson.co.uk>
Signed-off-by: Mika Kuoppala <mika.kuoppala at intel.com>
---
 drivers/gpu/drm/i915/i915_cmd_parser.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_cmd_parser.c b/drivers/gpu/drm/i915/i915_cmd_parser.c
index 9a6da35..61ae8ff 100644
--- a/drivers/gpu/drm/i915/i915_cmd_parser.c
+++ b/drivers/gpu/drm/i915/i915_cmd_parser.c
@@ -836,8 +836,11 @@ static u32 *vmap_batch(struct drm_i915_gem_object *obj,
 	}
 
 	i = 0;
-	for_each_sg_page(obj->pages->sgl, &sg_iter, npages, first_page)
+	for_each_sg_page(obj->pages->sgl, &sg_iter, obj->pages->nents, first_page) {
 		pages[i++] = sg_page_iter_page(&sg_iter);
+		if (i == npages)
+			break;
+	}
 
 	addr = vmap(pages, i, 0, PAGE_KERNEL);
 	if (addr == NULL) {
-- 
1.9.1