[PATCH v2 3/5] android: binder: Move buffer out of area shared with user space

[Sherry Yang]

Binder driver allocates buffer meta data in a region that is mapped
in user space. These meta data contain pointers in the kernel.

This patch allocates buffer meta data on the kernel heap that is
not mapped in user space, and uses a pointer to refer to the data mapped.

Signed-off-by: Sherry Yang <sherryy@xxxxxxxxxxx>
---
 drivers/android/binder_alloc.c          | 144 +++++++++++++++++++-------------
 drivers/android/binder_alloc.h          |   2 +-
 drivers/android/binder_alloc_selftest.c |  11 ++-
 3 files changed, 90 insertions(+), 67 deletions(-)

diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index f15af2b55a62..e96659215f25 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -62,9 +62,9 @@ static size_t binder_alloc_buffer_size(struct binder_alloc *alloc,
 				       struct binder_buffer *buffer)
 {
 	if (list_is_last(&buffer->entry, &alloc->buffers))
-		return alloc->buffer +
-		       alloc->buffer_size - (void *)buffer->data;
-	return (size_t)binder_buffer_next(buffer) - (size_t)buffer->data;
+		return (u8 *)alloc->buffer +
+			alloc->buffer_size - (u8 *)buffer->data;
+	return (u8 *)binder_buffer_next(buffer)->data - (u8 *)buffer->data;
 }
 
 static void binder_insert_free_buffer(struct binder_alloc *alloc,
@@ -114,9 +114,9 @@ static void binder_insert_allocated_buffer_locked(
 		buffer = rb_entry(parent, struct binder_buffer, rb_node);
 		BUG_ON(buffer->free);
 
-		if (new_buffer < buffer)
+		if (new_buffer->data < buffer->data)
 			p = &parent->rb_left;
-		else if (new_buffer > buffer)
+		else if (new_buffer->data > buffer->data)
 			p = &parent->rb_right;
 		else
 			BUG();
@@ -131,18 +131,17 @@ static struct binder_buffer *binder_alloc_prepare_to_free_locked(
 {
 	struct rb_node *n = alloc->allocated_buffers.rb_node;
 	struct binder_buffer *buffer;
-	struct binder_buffer *kern_ptr;
+	void *kern_ptr;
 
-	kern_ptr = (struct binder_buffer *)(user_ptr - alloc->user_buffer_offset
-		- offsetof(struct binder_buffer, data));
+	kern_ptr = (void *)(user_ptr - alloc->user_buffer_offset);
 
 	while (n) {
 		buffer = rb_entry(n, struct binder_buffer, rb_node);
 		BUG_ON(buffer->free);
 
-		if (kern_ptr < buffer)
+		if (kern_ptr < buffer->data)
 			n = n->rb_left;
-		else if (kern_ptr > buffer)
+		else if (kern_ptr > buffer->data)
 			n = n->rb_right;
 		else {
 			/*
@@ -330,6 +329,9 @@ struct binder_buffer *binder_alloc_new_buf_locked(struct binder_alloc *alloc,
 		return ERR_PTR(-ENOSPC);
 	}
 
+	/* Pad 0-size buffers so they get assigned unique addresses */
+	size = max(size, sizeof(void *));
+
 	while (n) {
 		buffer = rb_entry(n, struct binder_buffer, rb_node);
 		BUG_ON(!buffer->free);
@@ -389,14 +391,9 @@ struct binder_buffer *binder_alloc_new_buf_locked(struct binder_alloc *alloc,
 
 	has_page_addr =
 		(void *)(((uintptr_t)buffer->data + buffer_size) & PAGE_MASK);
-	if (n == NULL) {
-		if (size + sizeof(struct binder_buffer) + 4 >= buffer_size)
-			buffer_size = size; /* no room for other buffers */
-		else
-			buffer_size = size + sizeof(struct binder_buffer);
-	}
+	WARN_ON(n && buffer_size != size);
 	end_page_addr =
-		(void *)PAGE_ALIGN((uintptr_t)buffer->data + buffer_size);
+		(void *)PAGE_ALIGN((uintptr_t)buffer->data + size);
 	if (end_page_addr > has_page_addr)
 		end_page_addr = has_page_addr;
 	ret = binder_update_page_range(alloc, 1,
@@ -404,17 +401,25 @@ struct binder_buffer *binder_alloc_new_buf_locked(struct binder_alloc *alloc,
 	if (ret)
 		return ERR_PTR(ret);
 
-	rb_erase(best_fit, &alloc->free_buffers);
-	buffer->free = 0;
-	buffer->free_in_progress = 0;
-	binder_insert_allocated_buffer_locked(alloc, buffer);
 	if (buffer_size != size) {
-		struct binder_buffer *new_buffer = (void *)buffer->data + size;
+		struct binder_buffer *new_buffer;
 
+		new_buffer = kzalloc(sizeof(*buffer), GFP_KERNEL);
+		if (!new_buffer) {
+			pr_err("%s: %d failed to alloc new buffer struct\n",
+			       __func__, alloc->pid);
+			goto err_alloc_buf_struct_failed;
+		}
+		new_buffer->data = (u8 *)buffer->data + size;
 		list_add(&new_buffer->entry, &buffer->entry);
 		new_buffer->free = 1;
 		binder_insert_free_buffer(alloc, new_buffer);
 	}
+
+	rb_erase(best_fit, &alloc->free_buffers);
+	buffer->free = 0;
+	buffer->free_in_progress = 0;
+	binder_insert_allocated_buffer_locked(alloc, buffer);
 	binder_alloc_debug(BINDER_DEBUG_BUFFER_ALLOC,
 		     "%d: binder_alloc_buf size %zd got %pK\n",
 		      alloc->pid, size, buffer);
@@ -429,6 +434,12 @@ struct binder_buffer *binder_alloc_new_buf_locked(struct binder_alloc *alloc,
 			      alloc->pid, size, alloc->free_async_space);
 	}
 	return buffer;
+
+err_alloc_buf_struct_failed:
+	binder_update_page_range(alloc, 0,
+				 (void *)PAGE_ALIGN((uintptr_t)buffer->data),
+				 end_page_addr, NULL);
+	return ERR_PTR(-ENOMEM);
 }
 
 /**
@@ -463,56 +474,59 @@ struct binder_buffer *binder_alloc_new_buf(struct binder_alloc *alloc,
 
 static void *buffer_start_page(struct binder_buffer *buffer)
 {
-	return (void *)((uintptr_t)buffer & PAGE_MASK);
+	return (void *)((uintptr_t)buffer->data & PAGE_MASK);
 }
 
-static void *buffer_end_page(struct binder_buffer *buffer)
+static void *prev_buffer_end_page(struct binder_buffer *buffer)
 {
-	return (void *)(((uintptr_t)(buffer + 1) - 1) & PAGE_MASK);
+	return (void *)(((uintptr_t)(buffer->data) - 1) & PAGE_MASK);
 }
 
 static void binder_delete_free_buffer(struct binder_alloc *alloc,
 				      struct binder_buffer *buffer)
 {
 	struct binder_buffer *prev, *next = NULL;
-	int free_page_end = 1;
-	int free_page_start = 1;
-
+	bool to_free = true;
 	BUG_ON(alloc->buffers.next == &buffer->entry);
 	prev = binder_buffer_prev(buffer);
 	BUG_ON(!prev->free);
-	if (buffer_end_page(prev) == buffer_start_page(buffer)) {
-		free_page_start = 0;
-		if (buffer_end_page(prev) == buffer_end_page(buffer))
-			free_page_end = 0;
+	if (prev_buffer_end_page(prev) == buffer_start_page(buffer)) {
+		to_free = false;
 		binder_alloc_debug(BINDER_DEBUG_BUFFER_ALLOC,
-			     "%d: merge free, buffer %pK share page with %pK\n",
-			      alloc->pid, buffer, prev);
+				   "%d: merge free, buffer %pK share page with %pK\n",
+				   alloc->pid, buffer->data, prev->data);
 	}
 
 	if (!list_is_last(&buffer->entry, &alloc->buffers)) {
 		next = binder_buffer_next(buffer);
-		if (buffer_start_page(next) == buffer_end_page(buffer)) {
-			free_page_end = 0;
-			if (buffer_start_page(next) ==
-			    buffer_start_page(buffer))
-				free_page_start = 0;
+		if (buffer_start_page(next) == buffer_start_page(buffer)) {
+			to_free = false;
 			binder_alloc_debug(BINDER_DEBUG_BUFFER_ALLOC,
-				     "%d: merge free, buffer %pK share page with %pK\n",
-				      alloc->pid, buffer, prev);
+					   "%d: merge free, buffer %pK share page with %pK\n",
+					   alloc->pid,
+					   buffer->data,
+					   next->data);
 		}
 	}
-	list_del(&buffer->entry);
-	if (free_page_start || free_page_end) {
+
+	if (PAGE_ALIGNED(buffer->data)) {
+		binder_alloc_debug(BINDER_DEBUG_BUFFER_ALLOC,
+				   "%d: merge free, buffer start %pK is page aligned\n",
+				   alloc->pid, buffer->data);
+		to_free = false;
+	}
+
+	if (to_free) {
 		binder_alloc_debug(BINDER_DEBUG_BUFFER_ALLOC,
-			     "%d: merge free, buffer %pK do not share page%s%s with %pK or %pK\n",
-			     alloc->pid, buffer, free_page_start ? "" : " end",
-			     free_page_end ? "" : " start", prev, next);
-		binder_update_page_range(alloc, 0, free_page_start ?
-			buffer_start_page(buffer) : buffer_end_page(buffer),
-			(free_page_end ? buffer_end_page(buffer) :
-			buffer_start_page(buffer)) + PAGE_SIZE, NULL);
+				   "%d: merge free, buffer %pK do not share page with %pK or %pK\n",
+				   alloc->pid, buffer->data,
+				   prev->data, next->data);
+		binder_update_page_range(alloc, 0, buffer_start_page(buffer),
+					 buffer_start_page(buffer) + PAGE_SIZE,
+					 NULL);
 	}
+	list_del(&buffer->entry);
+	kfree(buffer);
 }
 
 static void binder_free_buf_locked(struct binder_alloc *alloc,
@@ -533,8 +547,8 @@ static void binder_free_buf_locked(struct binder_alloc *alloc,
 	BUG_ON(buffer->free);
 	BUG_ON(size > buffer_size);
 	BUG_ON(buffer->transaction != NULL);
-	BUG_ON((void *)buffer < alloc->buffer);
-	BUG_ON((void *)buffer > alloc->buffer + alloc->buffer_size);
+	BUG_ON(buffer->data < alloc->buffer);
+	BUG_ON(buffer->data > alloc->buffer + alloc->buffer_size);
 
 	if (buffer->async_transaction) {
 		alloc->free_async_space += size + sizeof(struct binder_buffer);
@@ -646,13 +660,14 @@ int binder_alloc_mmap_handler(struct binder_alloc *alloc,
 	}
 	alloc->buffer_size = vma->vm_end - vma->vm_start;
 
-	if (binder_update_page_range(alloc, 1, alloc->buffer,
-				     alloc->buffer + PAGE_SIZE, vma)) {
+	buffer = kzalloc(sizeof(*buffer), GFP_KERNEL);
+	if (!buffer) {
 		ret = -ENOMEM;
-		failure_string = "alloc small buf";
-		goto err_alloc_small_buf_failed;
+		failure_string = "alloc buffer struct";
+		goto err_alloc_buf_struct_failed;
 	}
-	buffer = alloc->buffer;
+
+	buffer->data = alloc->buffer;
 	INIT_LIST_HEAD(&alloc->buffers);
 	list_add(&buffer->entry, &alloc->buffers);
 	buffer->free = 1;
@@ -664,7 +679,7 @@ int binder_alloc_mmap_handler(struct binder_alloc *alloc,
 
 	return 0;
 
-err_alloc_small_buf_failed:
+err_alloc_buf_struct_failed:
 	kfree(alloc->pages);
 	alloc->pages = NULL;
 err_alloc_pages_failed:
@@ -684,14 +699,13 @@ void binder_alloc_deferred_release(struct binder_alloc *alloc)
 {
 	struct rb_node *n;
 	int buffers, page_count;
+	struct binder_buffer *buffer;
 
 	BUG_ON(alloc->vma);
 
 	buffers = 0;
 	mutex_lock(&alloc->mutex);
 	while ((n = rb_first(&alloc->allocated_buffers))) {
-		struct binder_buffer *buffer;
-
 		buffer = rb_entry(n, struct binder_buffer, rb_node);
 
 		/* Transaction should already have been freed */
@@ -701,6 +715,16 @@ void binder_alloc_deferred_release(struct binder_alloc *alloc)
 		buffers++;
 	}
 
+	while (!list_empty(&alloc->buffers)) {
+		buffer = list_first_entry(&alloc->buffers,
+					  struct binder_buffer, entry);
+		WARN_ON(!buffer->free);
+
+		list_del(&buffer->entry);
+		WARN_ON_ONCE(!list_empty(&alloc->buffers));
+		kfree(buffer);
+	}
+
 	page_count = 0;
 	if (alloc->pages) {
 		int i;
diff --git a/drivers/android/binder_alloc.h b/drivers/android/binder_alloc.h
index 4f02cc084c15..dd5649bf6469 100644
--- a/drivers/android/binder_alloc.h
+++ b/drivers/android/binder_alloc.h
@@ -57,7 +57,7 @@ struct binder_buffer {
 	size_t data_size;
 	size_t offsets_size;
 	size_t extra_buffers_size;
-	uint8_t data[0];
+	void *data;
 };
 
 /**
diff --git a/drivers/android/binder_alloc_selftest.c b/drivers/android/binder_alloc_selftest.c
index cc00ab6ee29d..0bf72079a9da 100644
--- a/drivers/android/binder_alloc_selftest.c
+++ b/drivers/android/binder_alloc_selftest.c
@@ -105,8 +105,9 @@ static bool check_buffer_pages_allocated(struct binder_alloc *alloc,
 	void *page_addr, *end;
 	int page_index;
 
-	end = (void *)PAGE_ALIGN((uintptr_t)buffer + size);
-	for (page_addr = buffer; page_addr < end; page_addr += PAGE_SIZE) {
+	end = (void *)PAGE_ALIGN((uintptr_t)buffer->data + size);
+	page_addr = buffer->data;
+	for (; page_addr < end; page_addr += PAGE_SIZE) {
 		page_index = (page_addr - alloc->buffer) / PAGE_SIZE;
 		if (!alloc->pages[page_index]) {
 			pr_err("incorrect alloc state at page index %d\n",
@@ -209,8 +210,7 @@ static void binder_selftest_alloc_size(struct binder_alloc *alloc,
 	 * Only BUFFER_NUM - 1 buffer sizes are adjustable since
 	 * we need one giant buffer before getting to the last page.
 	 */
-	back_sizes[0] += alloc->buffer_size - end_offset[BUFFER_NUM - 1]
-		- sizeof(struct binder_buffer) * BUFFER_NUM;
+	back_sizes[0] += alloc->buffer_size - end_offset[BUFFER_NUM - 1];
 	binder_selftest_free_seq(alloc, front_sizes, seq, 0);
 	binder_selftest_free_seq(alloc, back_sizes, seq, 0);
 }
@@ -228,8 +228,7 @@ static void binder_selftest_alloc_offset(struct binder_alloc *alloc,
 	prev = index == 0 ? 0 : end_offset[index - 1];
 	end = prev;
 
-	BUILD_BUG_ON((BUFFER_MIN_SIZE + sizeof(struct binder_buffer))
-		     * BUFFER_NUM >= PAGE_SIZE);
+	BUILD_BUG_ON(BUFFER_MIN_SIZE * BUFFER_NUM >= PAGE_SIZE);
 
 	for (align = SAME_PAGE_UNALIGNED; align < LOOP_END; align++) {
 		if (align % 2)
-- 
2.14.1.342.g6490525c54-goog