[PATCH v10 10/22] kasan: preassign tags to objects with ctors or SLAB_TYPESAFE_BY_RCU

[Andrey Konovalov]

An object constructor can initialize pointers within this objects based on
the address of the object. Since the object address might be tagged, we
need to assign a tag before calling constructor.

The implemented approach is to assign tags to objects with constructors
when a slab is allocated and call constructors once as usual. The
downside is that such object would always have the same tag when it is
reallocated, so we won't catch use-after-frees on it.

Also pressign tags for objects from SLAB_TYPESAFE_BY_RCU caches, since
they can be validy accessed after having been freed.

Reviewed-by: Andrey Ryabinin <aryabi...@virtuozzo.com>
Reviewed-by: Dmitry Vyukov <dvyu...@google.com>
Signed-off-by: Andrey Konovalov <andreyk...@google.com>
---
 mm/slab.c |  2 +-
 mm/slub.c | 24 ++++++++++++++----------
 2 files changed, 15 insertions(+), 11 deletions(-)

diff --git a/mm/slab.c b/mm/slab.c
index 26f60a22e5e0..27859fb39889 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -2574,7 +2574,7 @@ static void cache_init_objs(struct kmem_cache *cachep,
 
        for (i = 0; i < cachep->num; i++) {
                objp = index_to_obj(cachep, page, i);
-               kasan_init_slab_obj(cachep, objp);
+               objp = kasan_init_slab_obj(cachep, objp);
 
                /* constructor could break poison info */
                if (DEBUG == 0 && cachep->ctor) {
diff --git a/mm/slub.c b/mm/slub.c
index e739d46600b9..08740c3f3745 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1451,16 +1451,17 @@ static inline bool slab_free_freelist_hook(struct 
kmem_cache *s,
 #endif
 }
 
-static void setup_object(struct kmem_cache *s, struct page *page,
+static void *setup_object(struct kmem_cache *s, struct page *page,
                                void *object)
 {
        setup_object_debug(s, page, object);
-       kasan_init_slab_obj(s, object);
+       object = kasan_init_slab_obj(s, object);
        if (unlikely(s->ctor)) {
                kasan_unpoison_object_data(s, object);
                s->ctor(object);
                kasan_poison_object_data(s, object);
        }
+       return object;
 }
 
 /*
@@ -1568,16 +1569,16 @@ static bool shuffle_freelist(struct kmem_cache *s, 
struct page *page)
        /* First entry is used as the base of the freelist */
        cur = next_freelist_entry(s, page, &pos, start, page_limit,
                                freelist_count);
+       cur = setup_object(s, page, cur);
        page->freelist = cur;
 
        for (idx = 1; idx < page->objects; idx++) {
-               setup_object(s, page, cur);
                next = next_freelist_entry(s, page, &pos, start, page_limit,
                        freelist_count);
+               next = setup_object(s, page, next);
                set_freepointer(s, cur, next);
                cur = next;
        }
-       setup_object(s, page, cur);
        set_freepointer(s, cur, NULL);
 
        return true;
@@ -1599,7 +1600,7 @@ static struct page *allocate_slab(struct kmem_cache *s, 
gfp_t flags, int node)
        struct page *page;
        struct kmem_cache_order_objects oo = s->oo;
        gfp_t alloc_gfp;
-       void *start, *p;
+       void *start, *p, *next;
        int idx, order;
        bool shuffle;
 
@@ -1651,13 +1652,16 @@ static struct page *allocate_slab(struct kmem_cache *s, 
gfp_t flags, int node)
 
        if (!shuffle) {
                for_each_object_idx(p, idx, s, start, page->objects) {
-                       setup_object(s, page, p);
-                       if (likely(idx < page->objects))
-                               set_freepointer(s, p, p + s->size);
-                       else
+                       if (likely(idx < page->objects)) {
+                               next = p + s->size;
+                               next = setup_object(s, page, next);
+                               set_freepointer(s, p, next);
+                       } else
                                set_freepointer(s, p, NULL);
                }
-               page->freelist = fixup_red_left(s, start);
+               start = fixup_red_left(s, start);
+               start = setup_object(s, page, start);
+               page->freelist = start;
        }
 
        page->inuse = page->objects;
-- 
2.19.1.930.g4563a0d9d0-goog