Revert "android: binder: stop saving a pointer to the VMA"

commit c0fd2101781ef761b636769b2f445351f71c3626 upstream.

This reverts commit 6b44656517074b125afb72ca19f63ebc55235761.

This patch fixed an issue reported by syzkaller in [1]. However, this
turned out to be only a band-aid in binder. The root cause, as bisected
by syzkaller, was fixed by commit 8c37e6862a52 ("mm/mmap: undo ->mmap()
when mas_preallocate() fails"). We no longer need the patch for binder.

Reverting such patch allows us to have a lockless access to alloc->vma
in specific cases where the mmap_lock is not required. This approach
avoids the contention that caused a performance regression.

[1] https://lore.kernel.org/all/0000000000004a0dbe05e1d749e0@google.com

[cmllamas: resolved conflicts with rework of alloc->mm and removal of
 binder_alloc_set_vma() also fixed comment section]

Fixes: 6b4465651707 ("android: binder: stop saving a pointer to the VMA")
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Carlos Llamas <cmllamas@google.com>
Link: https://lore.kernel.org/r/20230502201220.1756319-2-cmllamas@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index 35c0cdfa816b325f348a84b66fe9ca812de6923b..acf510bb4d16b8c7ffd29680296049d766d5f4c3 100644 (file)
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -213,7 +213,7 @@ static int binder_update_page_range(struct binder_alloc *alloc, int allocate,
 
        if (mm) {
                mmap_read_lock(mm);
-               vma = vma_lookup(mm, alloc->vma_addr);
+               vma = alloc->vma;
        }
 
        if (!vma && need_mm) {
@@ -314,9 +314,11 @@ static inline struct vm_area_struct *binder_alloc_get_vma(
 {
        struct vm_area_struct *vma = NULL;
 
-       if (alloc->vma_addr)
-               vma = vma_lookup(alloc->mm, alloc->vma_addr);
-
+       if (alloc->vma) {
+               /* Look at description in binder_alloc_set_vma */
+               smp_rmb();
+               vma = alloc->vma;
+       }
        return vma;
 }
 
@@ -775,7 +777,7 @@ int binder_alloc_mmap_handler(struct binder_alloc *alloc,
        buffer->free = 1;
        binder_insert_free_buffer(alloc, buffer);
        alloc->free_async_space = alloc->buffer_size / 2;
-       alloc->vma_addr = vma->vm_start;
+       alloc->vma = vma;
 
        return 0;
 
@@ -805,8 +807,7 @@ void binder_alloc_deferred_release(struct binder_alloc *alloc)
 
        buffers = 0;
        mutex_lock(&alloc->mutex);
-       BUG_ON(alloc->vma_addr &&
-              vma_lookup(alloc->mm, alloc->vma_addr));
+       BUG_ON(alloc->vma);
 
        while ((n = rb_first(&alloc->allocated_buffers))) {
                buffer = rb_entry(n, struct binder_buffer, rb_node);
@@ -958,7 +959,7 @@ int binder_alloc_get_allocated_count(struct binder_alloc *alloc)
  */
 void binder_alloc_vma_close(struct binder_alloc *alloc)
 {
-       alloc->vma_addr = 0;
+       alloc->vma = 0;
 }
 
 /**

diff --git a/drivers/android/binder_alloc.h b/drivers/android/binder_alloc.h
index 0f811ac4bcffd1f922a6bd895cd5682ad9acd08c..138d1d5af9ce36051893ee50a8e728d7bfbc2940 100644 (file)
--- a/drivers/android/binder_alloc.h
+++ b/drivers/android/binder_alloc.h
@@ -75,7 +75,7 @@ struct binder_lru_page {
 /**
  * struct binder_alloc - per-binder proc state for binder allocator
  * @mutex:              protects binder_alloc fields
- * @vma_addr:           vm_area_struct->vm_start passed to mmap_handler
+ * @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
@@ -99,7 +99,7 @@ struct binder_lru_page {
  */
 struct binder_alloc {
        struct mutex mutex;
-       unsigned long vma_addr;
+       struct vm_area_struct *vma;
        struct mm_struct *mm;
        void __user *buffer;
        struct list_head buffers;

diff --git a/drivers/android/binder_alloc_selftest.c b/drivers/android/binder_alloc_selftest.c
index 43a881073a42832feb96c906c53e0ad34d2b2970..c2b323bc3b3a53043fa5783fb4f809de93b24644 100644 (file)
--- a/drivers/android/binder_alloc_selftest.c
+++ b/drivers/android/binder_alloc_selftest.c
@@ -287,7 +287,7 @@ void binder_selftest_alloc(struct binder_alloc *alloc)
        if (!binder_selftest_run)
                return;
        mutex_lock(&binder_selftest_lock);
-       if (!binder_selftest_run || !alloc->vma_addr)
+       if (!binder_selftest_run || !alloc->vma)
                goto done;
        pr_info("STARTED\n");
        binder_selftest_alloc_offset(alloc, end_offset, 0);