[PATCH v4 4/4] drm/i915/guc: Verify hwconfig blob matches supported format

[Jordan Justen]

i915_drm.h now defines the format of the returned
DRM_I915_QUERY_HWCONFIG_BLOB query item. Since i915 receives this from
the black box GuC software, it should verify that the data matches
that format before sending it to user-space.

The verification makes a single simple pass through the blob contents,
so this verification step should not add a significant amount of init
time to i915.

v3:
 * Add various changes suggested by Tvrtko

v4:
 * Rewrite verify_hwconfig_blob() to hopefully be clearer without
   relying on comments so much, and add various suggestions from
   Michal.

Signed-off-by: Jordan Justen <jordan.l.justen at intel.com>
Acked-by: Jon Bloomfield <jon.bloomfield at intel.com>
---
 .../gpu/drm/i915/gt/uc/intel_guc_hwconfig.c   | 44 ++++++++++++++++++-
 1 file changed, 43 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_hwconfig.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_hwconfig.c
index ce6088f112d4..7d5569d8d1e3 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_hwconfig.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_hwconfig.c
@@ -71,9 +71,46 @@ static int guc_hwconfig_discover_size(struct intel_guc_hwconfig *hwconfig)
 	return 0;
 }
 
+static int verify_hwconfig_blob(struct intel_guc_hwconfig *hwconfig)
+{
+	struct intel_guc *guc = hwconfig_to_guc(hwconfig);
+	struct drm_device *drm = &guc_to_gt(guc)->i915->drm;
+	struct drm_i915_query_hwconfig_blob_item *item = hwconfig->ptr;
+	u64 offset = 0;
+	u64 remaining = hwconfig->size;
+	/* Everything before the data field is required */
+	u64 min_item_size = offsetof(struct drm_i915_query_hwconfig_blob_item, data);
+	u64 item_size;
+
+	if (!IS_ALIGNED(hwconfig->size, sizeof(u32))) {
+		drm_err(drm, "hwconfig blob size (%d) is not u32 aligned\n", hwconfig->size);
+		return -EINVAL;
+	}
+
+	while (offset < hwconfig->size) {
+		if (remaining < min_item_size) {
+			drm_err(drm, "hwconfig blob invalid (no room for item required fields at offset %lld)\n",
+				offset);
+			return -EINVAL;
+		}
+		item_size = min_item_size + sizeof(u32) * item->length;
+		if (item_size > remaining) {
+			drm_err(drm, "hwconfig blob invalid (no room for data array of item at offset %lld)\n",
+				offset);
+			return -EINVAL;
+		}
+		offset += item_size;
+		remaining -= item_size;
+		item = (void *)&item->data[item->length];
+	}
+
+	return 0;
+}
+
 static int guc_hwconfig_fill_buffer(struct intel_guc_hwconfig *hwconfig)
 {
 	struct intel_guc *guc = hwconfig_to_guc(hwconfig);
+	struct drm_device *drm = &guc_to_gt(guc)->i915->drm;
 	struct i915_vma *vma;
 	u32 ggtt_offset;
 	void *vaddr;
@@ -88,8 +125,13 @@ static int guc_hwconfig_fill_buffer(struct intel_guc_hwconfig *hwconfig)
 	ggtt_offset = intel_guc_ggtt_offset(guc, vma);
 
 	ret = __guc_action_get_hwconfig(hwconfig, ggtt_offset, hwconfig->size);
-	if (ret >= 0)
+	if (ret >= 0) {
 		memcpy(hwconfig->ptr, vaddr, hwconfig->size);
+		if (verify_hwconfig_blob(hwconfig)) {
+			drm_err(drm, "Ignoring invalid hwconfig blob received from GuC!\n");
+			ret = -EINVAL;
+		}
+	}
 
 	i915_vma_unpin_and_release(&vma, I915_VMA_RELEASE_MAP);
 
-- 
2.34.1