linux-kernel - [PATCH v9 09/20] kasan: preassign tags to objects with ctors or SLAB_TYPESAFE_BY

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Message-Id: <9ea379b38a763adeae0e43638a9769c96eea767f.1537542735.git.andreyknvl@google.com>
Date:   Fri, 21 Sep 2018 17:13:31 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Christoph Lameter <cl@...ux.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mark Rutland <mark.rutland@....com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Marc Zyngier <marc.zyngier@....com>,
        Dave Martin <dave.martin@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Ingo Molnar <mingo@...nel.org>,
        Paul Lawrence <paullawrence@...gle.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Arnd Bergmann <arnd@...db.de>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        kasan-dev@...glegroups.com, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-sparse@...r.kernel.org, linux-mm@...ck.org,
        linux-kbuild@...r.kernel.org
Cc:     Kostya Serebryany <kcc@...gle.com>,
        Evgeniy Stepanov <eugenis@...gle.com>,
        Lee Smith <Lee.Smith@....com>,
        Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
        Jacob Bramley <Jacob.Bramley@....com>,
        Ruben Ayrapetyan <Ruben.Ayrapetyan@....com>,
        Jann Horn <jannh@...gle.com>,
        Mark Brand <markbrand@...gle.com>,
        Chintan Pandya <cpandya@...eaurora.org>,
        Vishwath Mohan <vishwath@...gle.com>,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: [PATCH v9 09/20] 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.

Signed-off-by: Andrey Konovalov <andreyknvl@...gle.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 6fdca9ec2ea4..fe0ddf08aa2c 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 c4d5f4442ff1..75fc76e42a1e 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1413,16 +1413,17 @@ 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;
 }
 
 /*
@@ -1530,16 +1531,16 @@ 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;
@@ -1561,7 +1562,7 @@ 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;
 
@@ -1613,13 +1614,16 @@ 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;
-- 
2.19.0.444.g18242da7ef-goog