It is unsafe to use alloc->vma outside of the mmap_sem. Instead, add a
new boolean alloc->mapped to save the vma state (mapped or unmmaped) and
use this to validate several paths. This change is in preparation for
removing the alloc->vma pointer in a subsequent patch.

Cc: Minchan Kim <minchan@kernel.org>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Carlos Llamas <cmllamas@google.com>
---
 drivers/android/binder_alloc.c          | 29 ++++++++++++++++++-------
 drivers/android/binder_alloc.h          |  2 ++
 drivers/android/binder_alloc_selftest.c |  2 +-
 3 files changed, 24 insertions(+), 9 deletions(-)

diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index 46789fa530a1..7239b92ef20a 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -220,6 +220,19 @@ static void binder_lru_freelist_add(struct binder_alloc *alloc,
 	}
 }
 
+static inline
+void binder_alloc_set_mapped(struct binder_alloc *alloc, bool state)
+{
+	/* pairs with smp_load_acquire in binder_alloc_is_mapped() */
+	smp_store_release(&alloc->mapped, state);
+}
+
+static inline bool binder_alloc_is_mapped(struct binder_alloc *alloc)
+{
+	/* pairs with smp_store_release in binder_alloc_set_mapped() */
+	return smp_load_acquire(&alloc->mapped);
+}
+
 static struct page *binder_page_alloc(struct binder_alloc *alloc,
 				      unsigned long index,
 				      unsigned long addr)
@@ -257,7 +270,7 @@ static int binder_install_single_page(struct binder_alloc *alloc,
 
 	mmap_read_lock(alloc->mm);
 	vma = vma_lookup(alloc->mm, addr);
-	if (!vma || vma != alloc->vma) {
+	if (!vma || !binder_alloc_is_mapped(alloc)) {
 		mmap_read_unlock(alloc->mm);
 		__free_page(page);
 		pr_err("%d: %s failed, no vma\n", alloc->pid, __func__);
@@ -611,7 +624,7 @@ struct binder_buffer *binder_alloc_new_buf(struct binder_alloc *alloc,
 	int ret;
 
 	/* Check binder_alloc is fully initialized */
-	if (!binder_alloc_get_vma(alloc)) {
+	if (!binder_alloc_is_mapped(alloc)) {
 		binder_alloc_debug(BINDER_DEBUG_USER_ERROR,
 				   "%d: binder_alloc_buf, no vma\n",
 				   alloc->pid);
@@ -893,7 +906,7 @@ int binder_alloc_mmap_handler(struct binder_alloc *alloc,
 	alloc->free_async_space = alloc->buffer_size / 2;
 
 	/* Signal binder_alloc is fully initialized */
-	binder_alloc_set_vma(alloc, vma);
+	binder_alloc_set_mapped(alloc, true);
 
 	return 0;
 
@@ -923,7 +936,7 @@ void binder_alloc_deferred_release(struct binder_alloc *alloc)
 
 	buffers = 0;
 	mutex_lock(&alloc->mutex);
-	BUG_ON(alloc->vma);
+	BUG_ON(alloc->mapped);
 
 	while ((n = rb_first(&alloc->allocated_buffers))) {
 		buffer = rb_entry(n, struct binder_buffer, rb_node);
@@ -1029,7 +1042,7 @@ void binder_alloc_print_pages(struct seq_file *m,
 	 * Make sure the binder_alloc is fully initialized, otherwise we might
 	 * read inconsistent state.
 	 */
-	if (binder_alloc_get_vma(alloc) != NULL) {
+	if (binder_alloc_is_mapped(alloc)) {
 		for (i = 0; i < alloc->buffer_size / PAGE_SIZE; i++) {
 			page = binder_get_installed_page(alloc, i);
 			if (!page)
@@ -1069,12 +1082,12 @@ int binder_alloc_get_allocated_count(struct binder_alloc *alloc)
  * @alloc: binder_alloc for this proc
  *
  * Called from binder_vma_close() when releasing address space.
- * Clears alloc->vma to prevent new incoming transactions from
+ * Clears alloc->mapped to prevent new incoming transactions from
  * allocating more buffers.
  */
 void binder_alloc_vma_close(struct binder_alloc *alloc)
 {
-	binder_alloc_set_vma(alloc, NULL);
+	binder_alloc_set_mapped(alloc, false);
 }
 
 /**
@@ -1111,7 +1124,7 @@ enum lru_status binder_alloc_free_page(struct list_head *item,
 	page_addr = alloc->buffer + index * PAGE_SIZE;
 
 	vma = vma_lookup(mm, page_addr);
-	if (vma && vma != binder_alloc_get_vma(alloc))
+	if (vma && !binder_alloc_is_mapped(alloc))
 		goto err_invalid_vma;
 
 	trace_binder_unmap_kernel_start(alloc, index);
diff --git a/drivers/android/binder_alloc.h b/drivers/android/binder_alloc.h
index 5c2473e95494..89f6fa25c670 100644
--- a/drivers/android/binder_alloc.h
+++ b/drivers/android/binder_alloc.h
@@ -75,6 +75,7 @@ struct binder_buffer {
  * @buffer_size:        size of address space specified via mmap
  * @pid:                pid for associated binder_proc (invariant after init)
  * @pages_high:         high watermark of offset in @pages
+ * @mapped:             whether the vm area is mapped
  * @oneway_spam_detected: %true if oneway spam detection fired, clear that
  * flag once the async buffer has returned to a healthy state
  *
@@ -96,6 +97,7 @@ struct binder_alloc {
 	size_t buffer_size;
 	int pid;
 	size_t pages_high;
+	bool mapped;
 	bool oneway_spam_detected;
 };
 
diff --git a/drivers/android/binder_alloc_selftest.c b/drivers/android/binder_alloc_selftest.c
index c6941b9abad9..2dda82d0d5e8 100644
--- a/drivers/android/binder_alloc_selftest.c
+++ b/drivers/android/binder_alloc_selftest.c
@@ -291,7 +291,7 @@ void binder_selftest_alloc(struct binder_alloc *alloc)
 	if (!binder_selftest_run)
 		return;
 	mutex_lock(&binder_selftest_lock);
-	if (!binder_selftest_run || !alloc->vma)
+	if (!binder_selftest_run || !alloc->mapped)
 		goto done;
 	pr_info("STARTED\n");
 	binder_selftest_alloc_offset(alloc, end_offset, 0);
-- 
2.47.0.199.ga7371fff76-goog