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Commit 4d176711 authored by Andrey Konovalov's avatar Andrey Konovalov Committed by Linus Torvalds
Browse files

kasan: preassign tags to objects with ctors or SLAB_TYPESAFE_BY_RCU 

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.

Link: http://lkml.kernel.org/r/f158a8a74a031d66f0a9398a5b0ed453c37ba09a.1544099024.git.andreyknvl@google.com


Signed-off-by: default avatarAndrey Konovalov <andreyknvl@google.com>
Reviewed-by: default avatarAndrey Ryabinin <aryabinin@virtuozzo.com>
Reviewed-by: default avatarDmitry Vyukov <dvyukov@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent e71fe3f9

mm/slab.c

+1 −1
Original line number Diff line number Diff line
@@ -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) {

mm/slub.c

+14 −10
Original line number Diff line number Diff line
@@ -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;