drm/i915: Trim the command parser allocations

Currently, the command parser tries to create a secondary batch exactly
as large as the original, and vmap both. This is open to abuse by
userspace using extremely large batch objects, but only executing very
short batches. For example, this would be if userspace were to implement
a command submission ringbuffer. However, we only need to allocate pages
for just the contents of the command sequence in the batch - all
relocations copied to the secondary batch will reference the original
batch and so there can be no access to the secondary batch outside of
the explicit execution region.

Testcase: igt/gem_exec_big #ivb,byt,hsw
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=88308
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: John Harrison <John.C.Harrison@Intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_cmd_parser.c

@@ -818,24 +818,26 @@ static bool valid_reg(const u32 *table, int count, u32 addr)
 	return false;
 }
 
-static u32 *vmap_batch(struct drm_i915_gem_object *obj)
+static u32 *vmap_batch(struct drm_i915_gem_object *obj,
+		       unsigned start, unsigned len)
 {
 	int i;
 	void *addr = NULL;
 	struct sg_page_iter sg_iter;
+	int first_page = start >> PAGE_SHIFT;
+	int last_page = (len + start + 4095) >> PAGE_SHIFT;
+	int npages = last_page - first_page;
 	struct page **pages;
 
-	pages = drm_malloc_ab(obj->base.size >> PAGE_SHIFT, sizeof(*pages));
+	pages = drm_malloc_ab(npages, sizeof(*pages));
 	if (pages == NULL) {
 		DRM_DEBUG_DRIVER("Failed to get space for pages\n");
 		goto finish;
 	}
 
 	i = 0;
-	for_each_sg_page(obj->pages->sgl, &sg_iter, obj->pages->nents, 0) {
-		pages[i] = sg_page_iter_page(&sg_iter);
-		i++;
-	}
+	for_each_sg_page(obj->pages->sgl, &sg_iter, npages, first_page)
+		pages[i++] = sg_page_iter_page(&sg_iter);
 
 	addr = vmap(pages, i, 0, PAGE_KERNEL);
 	if (addr == NULL) {
@@ -855,61 +857,61 @@ static u32 *copy_batch(struct drm_i915_gem_object *dest_obj,
 		       u32 batch_start_offset,
 		       u32 batch_len)
 {
-	int ret = 0;
 	int needs_clflush = 0;
-	u32 *src_base, *dest_base = NULL;
-	u32 *src_addr, *dest_addr;
-	u32 offset = batch_start_offset / sizeof(*dest_addr);
-	u32 end = batch_start_offset + batch_len;
+	void *src_base, *src;
+	void *dst = NULL;
+	int ret;
 
-	if (end > dest_obj->base.size || end > src_obj->base.size)
+	if (batch_len > dest_obj->base.size ||
+	    batch_len + batch_start_offset > src_obj->base.size)
 		return ERR_PTR(-E2BIG);
 
 	ret = i915_gem_obj_prepare_shmem_read(src_obj, &needs_clflush);
 	if (ret) {
-		DRM_DEBUG_DRIVER("CMD: failed to prep read\n");
+		DRM_DEBUG_DRIVER("CMD: failed to prepare shadow batch\n");
 		return ERR_PTR(ret);
 	}
 
-	src_base = vmap_batch(src_obj);
+	src_base = vmap_batch(src_obj, batch_start_offset, batch_len);
 	if (!src_base) {
 		DRM_DEBUG_DRIVER("CMD: Failed to vmap batch\n");
 		ret = -ENOMEM;
 		goto unpin_src;
 	}
 
-	src_addr = src_base + offset;
-
-	if (needs_clflush)
-		drm_clflush_virt_range((char *)src_addr, batch_len);
+	ret = i915_gem_object_get_pages(dest_obj);
+	if (ret) {
+		DRM_DEBUG_DRIVER("CMD: Failed to get pages for shadow batch\n");
+		goto unmap_src;
+	}
+	i915_gem_object_pin_pages(dest_obj);
 
 	ret = i915_gem_object_set_to_cpu_domain(dest_obj, true);
 	if (ret) {
-		DRM_DEBUG_DRIVER("CMD: Failed to set batch CPU domain\n");
+		DRM_DEBUG_DRIVER("CMD: Failed to set shadow batch to CPU\n");
 		goto unmap_src;
 	}
 
-	dest_base = vmap_batch(dest_obj);
-	if (!dest_base) {
+	dst = vmap_batch(dest_obj, 0, batch_len);
+	if (!dst) {
 		DRM_DEBUG_DRIVER("CMD: Failed to vmap shadow batch\n");
+		i915_gem_object_unpin_pages(dest_obj);
 		ret = -ENOMEM;
 		goto unmap_src;
 	}
 
-	dest_addr = dest_base + offset;
-
-	if (batch_start_offset != 0)
-		memset((u8 *)dest_base, 0, batch_start_offset);
+	src = src_base + offset_in_page(batch_start_offset);
+	if (needs_clflush)
+		drm_clflush_virt_range(src, batch_len);
 
-	memcpy(dest_addr, src_addr, batch_len);
-	memset((u8 *)dest_addr + batch_len, 0, dest_obj->base.size - end);
+	memcpy(dst, src, batch_len);
 
 unmap_src:
 	vunmap(src_base);
 unpin_src:
 	i915_gem_object_unpin_pages(src_obj);
 
-	return ret ? ERR_PTR(ret) : dest_base;
+	return ret ? ERR_PTR(ret) : dst;
 }
 
 /**
@@ -1046,34 +1048,26 @@ int i915_parse_cmds(struct intel_engine_cs *ring,
 		    u32 batch_len,
 		    bool is_master)
 {
-	int ret = 0;
 	u32 *cmd, *batch_base, *batch_end;
 	struct drm_i915_cmd_descriptor default_desc = { 0 };
 	bool oacontrol_set = false; /* OACONTROL tracking. See check_cmd() */
-
-	ret = i915_gem_obj_ggtt_pin(shadow_batch_obj, 4096, 0);
-	if (ret) {
-		DRM_DEBUG_DRIVER("CMD: Failed to pin shadow batch\n");
-		return -1;
-	}
+	int ret = 0;
 
 	batch_base = copy_batch(shadow_batch_obj, batch_obj,
 				batch_start_offset, batch_len);
 	if (IS_ERR(batch_base)) {
 		DRM_DEBUG_DRIVER("CMD: Failed to copy batch\n");
-		i915_gem_object_ggtt_unpin(shadow_batch_obj);
 		return PTR_ERR(batch_base);
 	}
 
-	cmd = batch_base + (batch_start_offset / sizeof(*cmd));
-
 	/*
 	 * We use the batch length as size because the shadow object is as
 	 * large or larger and copy_batch() will write MI_NOPs to the extra
 	 * space. Parsing should be faster in some cases this way.
 	 */
-	batch_end = cmd + (batch_len / sizeof(*batch_end));
+	batch_end = batch_base + (batch_len / sizeof(*batch_end));
 
+	cmd = batch_base;
 	while (cmd < batch_end) {
 		const struct drm_i915_cmd_descriptor *desc;
 		u32 length;
@@ -1132,7 +1126,7 @@ int i915_parse_cmds(struct intel_engine_cs *ring,
 	}
 
 	vunmap(batch_base);
-	i915_gem_object_ggtt_unpin(shadow_batch_obj);
+	i915_gem_object_unpin_pages(shadow_batch_obj);
 
 	return ret;
 }

drivers/gpu/drm/i915/i915_gem_execbuffer.c

@@ -1076,16 +1076,15 @@ i915_gem_execbuffer_parse(struct intel_engine_cs *ring,
 			  struct drm_i915_gem_object *batch_obj,
 			  u32 batch_start_offset,
 			  u32 batch_len,
-			  bool is_master,
-			  u32 *flags)
+			  bool is_master)
 {
 	struct drm_i915_private *dev_priv = to_i915(batch_obj->base.dev);
 	struct drm_i915_gem_object *shadow_batch_obj;
-	bool need_reloc = false;
+	struct i915_vma *vma;
 	int ret;
 
 	shadow_batch_obj = i915_gem_batch_pool_get(&dev_priv->mm.batch_pool,
-						   batch_obj->base.size);
+						   PAGE_ALIGN(batch_len));
 	if (IS_ERR(shadow_batch_obj))
 		return shadow_batch_obj;
 
@@ -1095,40 +1094,30 @@ i915_gem_execbuffer_parse(struct intel_engine_cs *ring,
 			      batch_start_offset,
 			      batch_len,
 			      is_master);
-	if (ret) {
-		if (ret == -EACCES)
-			return batch_obj;
-	} else {
-		struct i915_vma *vma;
+	if (ret)
+		goto err;
 
-		memset(shadow_exec_entry, 0, sizeof(*shadow_exec_entry));
+	ret = i915_gem_obj_ggtt_pin(shadow_batch_obj, 0, 0);
+	if (ret)
+		goto err;
 
-		vma = i915_gem_obj_to_ggtt(shadow_batch_obj);
-		vma->exec_entry = shadow_exec_entry;
-		vma->exec_entry->flags = __EXEC_OBJECT_PURGEABLE;
-		drm_gem_object_reference(&shadow_batch_obj->base);
-		i915_gem_execbuffer_reserve_vma(vma, ring, &need_reloc);
-		list_add_tail(&vma->exec_list, &eb->vmas);
+	memset(shadow_exec_entry, 0, sizeof(*shadow_exec_entry));
 
-		shadow_batch_obj->base.pending_read_domains =
-			batch_obj->base.pending_read_domains;
+	vma = i915_gem_obj_to_ggtt(shadow_batch_obj);
+	vma->exec_entry = shadow_exec_entry;
+	vma->exec_entry->flags = __EXEC_OBJECT_PURGEABLE | __EXEC_OBJECT_HAS_PIN;
+	drm_gem_object_reference(&shadow_batch_obj->base);
+	list_add_tail(&vma->exec_list, &eb->vmas);
 
-		/*
-		 * Set the DISPATCH_SECURE bit to remove the NON_SECURE
-		 * bit from MI_BATCH_BUFFER_START commands issued in the
-		 * dispatch_execbuffer implementations. We specifically
-		 * don't want that set when the command parser is
-		 * enabled.
-		 *
-		 * FIXME: with aliasing ppgtt, buffers that should only
-		 * be in ggtt still end up in the aliasing ppgtt. remove
-		 * this check when that is fixed.
-		 */
-		if (USES_FULL_PPGTT(dev))
-			*flags |= I915_DISPATCH_SECURE;
-	}
+	shadow_batch_obj->base.pending_read_domains = I915_GEM_DOMAIN_COMMAND;
+
+	return shadow_batch_obj;
 
-	return ret ? ERR_PTR(ret) : shadow_batch_obj;
+err:
+	if (ret == -EACCES) /* unhandled chained batch */
+		return batch_obj;
+	else
+		return ERR_PTR(ret);
 }
 
 int
@@ -1494,12 +1483,27 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data,
 						      batch_obj,
 						      args->batch_start_offset,
 						      args->batch_len,
-						      file->is_master,
-						      &flags);
+						      file->is_master);
 		if (IS_ERR(batch_obj)) {
 			ret = PTR_ERR(batch_obj);
 			goto err;
 		}
+
+		/*
+		 * Set the DISPATCH_SECURE bit to remove the NON_SECURE
+		 * bit from MI_BATCH_BUFFER_START commands issued in the
+		 * dispatch_execbuffer implementations. We specifically
+		 * don't want that set when the command parser is
+		 * enabled.
+		 *
+		 * FIXME: with aliasing ppgtt, buffers that should only
+		 * be in ggtt still end up in the aliasing ppgtt. remove
+		 * this check when that is fixed.
+		 */
+		if (USES_FULL_PPGTT(dev))
+			flags |= I915_DISPATCH_SECURE;
+
+		exec_start = 0;
 	}
 
 	batch_obj->base.pending_read_domains |= I915_GEM_DOMAIN_COMMAND;