[PATCH 09/10] android: binder: support for scatter-gather.

[Martijn Coenen]

Previously all data passed over binder needed
to be serialized, with the exception of Binder
objects and file descriptors.

This patchs adds support for scatter-gathering raw
memory buffers into a binder transaction, avoiding
the need to first serialize them into a Parcel.

To remain backwards compatibile with existing
binder clients, it introduces two new command
ioctls for this purpose - BC_TRANSACTION_SG and
BC_REPLY_SG. These commands may only be used with
the new binder_transaction_data_sg structure,
which adds a field for the total size of the
buffers we are scatter-gathering.

Because memory buffers may contain pointers to
other buffers, we allow callers to specify
a parent buffer and an offset into it, to indicate
this is a location pointing to the buffer that
we are fixing up. The kernel will then take care
of fixing up the pointer to that buffer as well.

Signed-off-by: Martijn Coenen <maco@xxxxxxxxxxx>
---
 drivers/android/binder.c            | 244 ++++++++++++++++++++++++++++++++++--
 include/uapi/linux/android/binder.h |  44 +++++++
 2 files changed, 275 insertions(+), 13 deletions(-)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 18a3254..76dda7b 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -152,6 +152,9 @@ module_param_call(stop_on_user_error, binder_set_stop_on_user_error,
 
 #define to_binder_fd_object(hdr) container_of(hdr, struct binder_fd_object, hdr)
 
+#define to_binder_buffer_object(hdr) \
+	container_of(hdr, struct binder_buffer_object, hdr)
+
 enum binder_stat_types {
 	BINDER_STAT_PROC,
 	BINDER_STAT_THREAD,
@@ -165,7 +168,7 @@ enum binder_stat_types {
 
 struct binder_stats {
 	int br[_IOC_NR(BR_FAILED_REPLY) + 1];
-	int bc[_IOC_NR(BC_DEAD_BINDER_DONE) + 1];
+	int bc[_IOC_NR(BC_REPLY_SG) + 1];
 	int obj_created[BINDER_STAT_COUNT];
 	int obj_deleted[BINDER_STAT_COUNT];
 };
@@ -1305,6 +1308,9 @@ static size_t binder_validate_object(struct binder_buffer *buffer, u64 offset)
 	case BINDER_TYPE_FD:
 		object_size = sizeof(struct binder_fd_object);
 		break;
+	case BINDER_TYPE_PTR:
+		object_size = sizeof(struct binder_buffer_object);
+		break;
 	default:
 		return 0;
 	}
@@ -1315,11 +1321,111 @@ static size_t binder_validate_object(struct binder_buffer *buffer, u64 offset)
 		return 0;
 }
 
+/**
+ * binder_validate_ptr() - validates binder_buffer_object in a binder_buffer.
+ * @b:		binder_buffer containing the object
+ * @index:	index in offset array at which the binder_buffer_object is
+ *		located
+ * @start:	points to the start of the offset array
+ * @num_valid:	the number of valid offsets in the offset array
+ *
+ * Return:	If @index is within the valid range of the offset array
+ *		described by @start and @num_valid, and if there's a valid
+ *		binder_buffer_object at the offset found in index @index
+ *		of the offset array, that object is returned. Otherwise,
+ *		%NULL is returned.
+ *		Note that the offset found in index @index itself is not
+ *		verified; this function assumes that @num_valid elements
+ *		from @start were previously verified to have valid offsets.
+ */
+static struct binder_buffer_object *binder_validate_ptr(struct binder_buffer *b,
+							binder_size_t index,
+							binder_size_t *start,
+							binder_size_t num_valid)
+{
+	struct binder_buffer_object *buffer_obj;
+	binder_size_t *offp;
+
+	if (index >= num_valid)
+		return NULL;
+
+	offp = start + index;
+	buffer_obj = (struct binder_buffer_object *)(b->data + *offp);
+	if (buffer_obj->hdr.type != BINDER_TYPE_PTR)
+		return NULL;
+
+	return buffer_obj;
+}
+
+/**
+ * binder_validate_fixup() - validates pointer/fd fixups happen in order.
+ * @b:			transaction buffer
+ * @objects_start	start of objects buffer
+ * @buffer:		binder_buffer_object in which to fix up
+ * @offset:		start offset in @buffer to fix up
+ * @last_obj:		last binder_buffer_object that we fixed up in
+ * @last_min_offset:	minimum fixup offset in @last_obj
+ *
+ * Return:		%true if a fixup in buffer @buffer at offset @offset is
+ *			allowed.
+ *
+ * For safety reasons, we only allow fixups inside a buffer to happen
+ * at increasing offsets; additionally, we only allow fixup on the last
+ * buffer object that was verified, or one of its parents.
+ *
+ * Example of what is allowed:
+ *
+ * A
+ *   B (parent = A, offset = 0)
+ *   C (parent = A, offset = 16)
+ *     D (parent = C, offset = 0)
+ *   E (parent = A, offset = 32) // min_offset is 16 (C.parent_offset)
+ *
+ * Examples of what is not allowed:
+ *
+ * Decreasing offsets within the same parent:
+ * A
+ *   C (parent = A, offset = 16)
+ *   B (parent = A, offset = 0) // decreasing offset within A
+ *
+ * Referring to a parent that wasn't the last object or any of its parents:
+ * A
+ *   B (parent = A, offset = 0)
+ *   C (parent = A, offset = 0)
+ *   C (parent = A, offset = 16)
+ *     D (parent = B, offset = 0) // B is not A or any of A's parents
+ */
+static bool binder_validate_fixup(struct binder_buffer *b,
+				  binder_size_t *objects_start,
+				  struct binder_buffer_object *buffer,
+				  binder_size_t fixup_offset,
+				  struct binder_buffer_object *last_obj,
+				  binder_size_t last_min_offset)
+{
+	if (!last_obj) {
+		/* Nothing to fix up in */
+		return false;
+	}
+
+	while (last_obj != buffer) {
+		/*
+		 * Safe to retrieve the parent of last_obj, since it
+		 * was already previously verified by the driver.
+		 */
+		if ((last_obj->flags & BINDER_BUFFER_FLAG_HAS_PARENT) == 0)
+			return false;
+		last_min_offset = last_obj->parent_offset + sizeof(uintptr_t);
+		last_obj = (struct binder_buffer_object *)
+			(b->data + *(objects_start + last_obj->parent));
+	}
+	return (fixup_offset >= last_min_offset);
+}
+
 static void binder_transaction_buffer_release(struct binder_proc *proc,
 					      struct binder_buffer *buffer,
 					      binder_size_t *failed_at)
 {
-	binder_size_t *offp, *off_end;
+	binder_size_t *offp, *off_start, *off_end;
 	int debug_id = buffer->debug_id;
 
 	binder_debug(BINDER_DEBUG_TRANSACTION,
@@ -1330,13 +1436,13 @@ static void binder_transaction_buffer_release(struct binder_proc *proc,
 	if (buffer->target_node)
 		binder_dec_node(buffer->target_node, 1, 0);
 
-	offp = (binder_size_t *)(buffer->data +
-				 ALIGN(buffer->data_size, sizeof(void *)));
+	off_start = (binder_size_t *)(buffer->data +
+				      ALIGN(buffer->data_size, sizeof(void *)));
 	if (failed_at)
 		off_end = failed_at;
 	else
-		off_end = (void *)offp + buffer->offsets_size;
-	for (; offp < off_end; offp++) {
+		off_end = (void *)off_start + buffer->offsets_size;
+	for (offp = off_start; offp < off_end; offp++) {
 		struct binder_object_header *hdr;
 		size_t object_size = binder_validate_object(buffer, *offp);
 
@@ -1392,7 +1498,12 @@ static void binder_transaction_buffer_release(struct binder_proc *proc,
 			if (failed_at)
 				task_close_fd(proc, fp->fd);
 		} break;
-
+		case BINDER_TYPE_PTR:
+			/*
+			 * Nothing to do here, this will get cleaned up when the
+			 * transaction buffer gets freed
+			 */
+			break;
 		default:
 			pr_err("transaction release %d bad object type %x\n",
 				debug_id, hdr->type);
@@ -1562,6 +1673,53 @@ static int binder_translate_fd(int fd,
 	return ret;
 }
 
+static int binder_fixup_parent(struct binder_transaction *t,
+			       struct binder_thread *thread,
+			       struct binder_buffer_object *bp,
+			       binder_size_t *off_start,
+			       binder_size_t num_valid,
+			       struct binder_buffer_object *last_fixup_obj,
+			       binder_size_t last_fixup_min_off)
+{
+	struct binder_buffer_object *parent;
+	u8 *parent_buffer;
+	struct binder_buffer *b = t->buffer;
+	struct binder_proc *proc = thread->proc;
+	struct binder_proc *target_proc = t->to_proc;
+
+	if (!(bp->flags & BINDER_BUFFER_FLAG_HAS_PARENT))
+		return 0;
+
+	parent = binder_validate_ptr(b, bp->parent, off_start, num_valid);
+	if (!parent) {
+		binder_user_error("%d:%d got transaction with invalid parent offset or type\n",
+				  proc->pid, thread->pid);
+		return -EINVAL;
+	}
+
+	if (!binder_validate_fixup(b, off_start,
+				   parent, bp->parent_offset,
+				   last_fixup_obj,
+				   last_fixup_min_off)) {
+		binder_user_error("%d:%d got transaction with out-of-order buffer fixup\n",
+				  proc->pid, thread->pid);
+		return -EINVAL;
+	}
+
+	if (parent->length < sizeof(binder_uintptr_t) ||
+	    bp->parent_offset > parent->length - sizeof(binder_uintptr_t)) {
+		/* No space for a pointer here! */
+		binder_user_error("%d:%d got transaction with invalid parent offset\n",
+				  proc->pid, thread->pid);
+		return -EINVAL;
+	}
+	parent_buffer = (u8 *)(parent->buffer -
+			       target_proc->user_buffer_offset);
+	*(binder_uintptr_t *)(parent_buffer + bp->parent_offset) = bp->buffer;
+
+	return 0;
+}
+
 static void binder_transaction(struct binder_proc *proc,
 			       struct binder_thread *thread,
 			       struct binder_transaction_data *tr, int reply,
@@ -1570,8 +1728,9 @@ static void binder_transaction(struct binder_proc *proc,
 	int ret;
 	struct binder_transaction *t;
 	struct binder_work *tcomplete;
-	binder_size_t *offp, *off_end;
+	binder_size_t *offp, *off_end, *off_start;
 	binder_size_t off_min;
+	u8 *sg_bufp, *sg_buf_end;
 	struct binder_proc *target_proc;
 	struct binder_thread *target_thread = NULL;
 	struct binder_node *target_node = NULL;
@@ -1580,6 +1739,8 @@ static void binder_transaction(struct binder_proc *proc,
 	struct binder_transaction *in_reply_to = NULL;
 	struct binder_transaction_log_entry *e;
 	uint32_t return_error;
+	struct binder_buffer_object *last_fixup_obj = NULL;
+	binder_size_t last_fixup_min_off = 0;
 	struct binder_context *context = proc->context;
 
 	e = binder_transaction_log_add(&binder_transaction_log);
@@ -1754,8 +1915,9 @@ static void binder_transaction(struct binder_proc *proc,
 	if (target_node)
 		binder_inc_node(target_node, 1, 0, NULL);
 
-	offp = (binder_size_t *)(t->buffer->data +
-				 ALIGN(tr->data_size, sizeof(void *)));
+	off_start = (binder_size_t *)(t->buffer->data +
+				      ALIGN(tr->data_size, sizeof(void *)));
+	offp = off_start;
 
 	if (copy_from_user(t->buffer->data, (const void __user *)(uintptr_t)
 			   tr->data.ptr.buffer, tr->data_size)) {
@@ -1777,7 +1939,16 @@ static void binder_transaction(struct binder_proc *proc,
 		return_error = BR_FAILED_REPLY;
 		goto err_bad_offset;
 	}
-	off_end = (void *)offp + tr->offsets_size;
+	if (!IS_ALIGNED(extra_buffers_size, sizeof(u64))) {
+		binder_user_error("%d:%d got transaction with unaligned buffers size, %lld\n",
+				  proc->pid, thread->pid,
+				  extra_buffers_size);
+		return_error = BR_FAILED_REPLY;
+		goto err_bad_offset;
+	}
+	off_end = (void *)off_start + tr->offsets_size;
+	sg_bufp = (u8 *)(PTR_ALIGN(off_end, sizeof(void *)));
+	sg_buf_end = sg_bufp + extra_buffers_size;
 	off_min = 0;
 	for (; offp < off_end; offp++) {
 		struct binder_object_header *hdr;
@@ -1830,7 +2001,41 @@ static void binder_transaction(struct binder_proc *proc,
 			fp->pad_binder = 0;
 			fp->fd = target_fd;
 		} break;
-
+		case BINDER_TYPE_PTR: {
+			struct binder_buffer_object *bp =
+				to_binder_buffer_object(hdr);
+			size_t buf_left = sg_buf_end - sg_bufp;
+
+			if (bp->length > buf_left) {
+				binder_user_error("%d:%d got transaction with too large buffer\n",
+						  proc->pid, thread->pid);
+				return_error = BR_FAILED_REPLY;
+				goto err_bad_offset;
+			}
+			if (copy_from_user(sg_bufp,
+					   (const void __user *)(uintptr_t)
+					   bp->buffer, bp->length)) {
+				binder_user_error("%d:%d got transaction with invalid offsets ptr\n",
+						  proc->pid, thread->pid);
+				return_error = BR_FAILED_REPLY;
+				goto err_copy_data_failed;
+			}
+			/* Fixup buffer pointer to target proc address space */
+			bp->buffer = (uintptr_t)sg_bufp +
+				target_proc->user_buffer_offset;
+			sg_bufp += ALIGN(bp->length, sizeof(u64));
+
+			ret = binder_fixup_parent(t, thread, bp, off_start,
+						  offp - off_start,
+						  last_fixup_obj,
+						  last_fixup_min_off);
+			if (ret < 0) {
+				return_error = BR_FAILED_REPLY;
+				goto err_translate_failed;
+			}
+			last_fixup_obj = bp;
+			last_fixup_min_off = 0;
+		} break;
 		default:
 			binder_user_error("%d:%d got transaction with invalid object type, %x\n",
 				proc->pid, thread->pid, hdr->type);
@@ -2084,6 +2289,17 @@ static int binder_thread_write(struct binder_proc *proc,
 			break;
 		}
 
+		case BC_TRANSACTION_SG:
+		case BC_REPLY_SG: {
+			struct binder_transaction_data_sg tr;
+
+			if (copy_from_user(&tr, ptr, sizeof(tr)))
+				return -EFAULT;
+			ptr += sizeof(tr);
+			binder_transaction(proc, thread, &tr.transaction_data,
+					   cmd == BC_REPLY_SG, tr.buffers_size);
+			break;
+		}
 		case BC_TRANSACTION:
 		case BC_REPLY: {
 			struct binder_transaction_data tr;
@@ -3610,7 +3826,9 @@ static const char * const binder_command_strings[] = {
 	"BC_EXIT_LOOPER",
 	"BC_REQUEST_DEATH_NOTIFICATION",
 	"BC_CLEAR_DEATH_NOTIFICATION",
-	"BC_DEAD_BINDER_DONE"
+	"BC_DEAD_BINDER_DONE",
+	"BC_TRANSACTION_SG",
+	"BC_REPLY_SG",
 };
 
 static const char * const binder_objstat_strings[] = {
diff --git a/include/uapi/linux/android/binder.h b/include/uapi/linux/android/binder.h
index f67c2b1..15d8395 100644
--- a/include/uapi/linux/android/binder.h
+++ b/include/uapi/linux/android/binder.h
@@ -33,6 +33,7 @@ enum {
 	BINDER_TYPE_HANDLE	= B_PACK_CHARS('s', 'h', '*', B_TYPE_LARGE),
 	BINDER_TYPE_WEAK_HANDLE	= B_PACK_CHARS('w', 'h', '*', B_TYPE_LARGE),
 	BINDER_TYPE_FD		= B_PACK_CHARS('f', 'd', '*', B_TYPE_LARGE),
+	BINDER_TYPE_PTR		= B_PACK_CHARS('p', 't', '*', B_TYPE_LARGE),
 };
 
 enum {
@@ -95,6 +96,39 @@ struct binder_fd_object {
 
 	binder_uintptr_t		cookie;
 };
+
+/* struct binder_buffer_object - object describing a userspace buffer
+ * @hdr:		common header structure
+ * @flags:		one or more BINDER_BUFFER_* flags
+ * @buffer:		address of the buffer
+ * @length:		length of the buffer
+ * @parent:		index in offset array pointing to parent buffer
+ * @parent_offset:	offset in @parent pointing to this buffer
+ *
+ * A binder_buffer object represents an object that the
+ * binder kernel driver can copy verbatim to the target
+ * address space. A buffer itself may be pointed to from
+ * within another buffer, meaning that the pointer inside
+ * that other buffer needs to be fixed up as well. This
+ * can be done by setting the BINDER_BUFFER_FLAG_HAS_PARENT
+ * flag in @flags, by setting @parent buffer to the index
+ * in the offset array pointing to the parent binder_buffer_object,
+ * and by setting @parent_offset to the offset in the parent buffer
+ * at which the pointer to this buffer is located.
+ */
+struct binder_buffer_object {
+	struct binder_object_header	hdr;
+	__u32				flags;
+	binder_uintptr_t		buffer;
+	binder_size_t			length;
+	binder_size_t			parent;
+	binder_size_t			parent_offset;
+};
+
+enum {
+	BINDER_BUFFER_FLAG_HAS_PARENT = 0x01,
+};
+
 /*
  * On 64-bit platforms where user code may run in 32-bits the driver must
  * translate the buffer (and local binder) addresses appropriately.
@@ -187,6 +221,11 @@ struct binder_transaction_data {
 	} data;
 };
 
+struct binder_transaction_data_sg {
+	struct binder_transaction_data transaction_data;
+	binder_size_t buffers_size;
+};
+
 struct binder_ptr_cookie {
 	binder_uintptr_t ptr;
 	binder_uintptr_t cookie;
@@ -371,6 +410,11 @@ enum binder_driver_command_protocol {
 	/*
 	 * void *: cookie
 	 */
+	BC_TRANSACTION_SG = _IOW('c', 17, struct binder_transaction_data_sg),
+	BC_REPLY_SG = _IOW('c', 18, struct binder_transaction_data_sg),
+	/*
+	 * binder_transaction_data_sg: the sent command.
+	 */
 };
 
 #endif /* _UAPI_LINUX_BINDER_H */
-- 
2.8.0.rc3.226.g39d4020