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Subject[PATCH v13 12/25] kasan: preassign tags to objects with ctors or SLAB_TYPESAFE_BY_RCU
Date
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 <aryabinin@virtuozzo.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Andrey Konovalov <andreyknvl@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;
--
2.20.0.rc1.387.gf8505762e3-goog
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