[PATCH v6 5/9] binder: replace alloc->vma with alloc->mapped

Carlos Llamas
2024-12-03T21:55:26Z

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 as a replacement for alloc->vma to validate several paths.

Using the alloc->vma caused several performance and security issues in
the past. Now that it has been replaced with either vm_lookup() or the
alloc->mapped state, we can finally remove it.

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>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Carlos Llamas <cmllamas@google.com>
---
drivers/android/binder_alloc.c | 48 +++++++++++++------------
drivers/android/binder_alloc.h | 6 ++--
drivers/android/binder_alloc_selftest.c | 2 +-
3 files changed, 30 insertions(+), 26 deletions(-)

diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index fd82ecefd961..60ca0e541d6f 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)
{
@@ -271,7 +284,7 @@ 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)) {
binder_free_page(page);
pr_err("%d: %s failed, no vma\n", alloc->pid, __func__);
ret = -ESRCH;
@@ -379,20 +392,6 @@ static void binder_lru_freelist_del(struct binder_alloc *alloc,
}
}

-static inline void binder_alloc_set_vma(struct binder_alloc *alloc,
- struct vm_area_struct *vma)
-{
- /* pairs with smp_load_acquire in binder_alloc_get_vma() */
- smp_store_release(&alloc->vma, vma);
-}
-
-static inline struct vm_area_struct *binder_alloc_get_vma(
- struct binder_alloc *alloc)
-{
- /* pairs with smp_store_release in binder_alloc_set_vma() */
- return smp_load_acquire(&alloc->vma);
-}
-
static void debug_no_space_locked(struct binder_alloc *alloc)
{
size_t largest_alloc_size = 0;
@@ -626,7 +625,7 @@ 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);
@@ -908,7 +907,7 @@ 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;

@@ -938,7 +937,7 @@ 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);
@@ -1044,7 +1043,7 @@ 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)
@@ -1084,12 +1083,12 @@ 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);
}

/**
@@ -1125,7 +1124,12 @@ 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))
+ /*
+ * Since a binder_alloc can only be mapped once, we ensure
+ * the vma corresponds to this mapping by checking whether
+ * the binder_alloc is still mapped.
+ */
+ 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 d71f99189ef5..3ebb12afd4de 100644
--- a/drivers/android/binder_alloc.h
+++ b/drivers/android/binder_alloc.h
@@ -82,8 +82,6 @@ static inline struct list_head *page_to_lru(struct page *p)
/**
* struct binder_alloc - per-binder proc state for binder allocator
* @mutex: protects binder_alloc fields
- * @vma: vm_area_struct passed to mmap_handler
- * (invariant after mmap)
* @mm: copy of task->mm (invariant after open)
* @buffer: base of per-proc address space mapped via mmap
* @buffers: list of all buffers for this proc
@@ -96,6 +94,8 @@ static inline struct list_head *page_to_lru(struct page *p)
* @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, each binder instance is
+ * allowed a single mapping throughout its lifetime
* @oneway_spam_detected: %true if oneway spam detection fired, clear that
* flag once the async buffer has returned to a healthy state
*
@@ -106,7 +106,6 @@ static inline struct list_head *page_to_lru(struct page *p)
*/
struct binder_alloc {
struct mutex mutex;
- struct vm_area_struct *vma;
struct mm_struct *mm;
unsigned long buffer;
struct list_head buffers;
@@ -117,6 +116,7 @@ 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 a4c650843bee..6a64847a8555 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);
--
2.47.0.338.g60cca15819-goog