linux-kernel - [PATCH 3/4] kasan, slab: make freelist stored without tags

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Message-Id: <dfb53b44a4d00de3879a05a9f04c1f55e584f7a1.1550602886.git.andreyknvl@google.com>
Date:   Wed, 20 Feb 2019 13:45:28 +0100
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>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        kasan-dev@...glegroups.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Cc:     Qian Cai <cai@....pw>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Kostya Serebryany <kcc@...gle.com>,
        Evgeniy Stepanov <eugenis@...gle.com>,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: [PATCH 3/4] kasan, slab: make freelist stored without tags

Similarly to 680c37ae ("kasan, slub: move kasan_poison_slab hook before
page_address"), move kasan_poison_slab() before alloc_slabmgmt(), which
calls page_address(), to make page_address() return value to be
non-tagged. This, combined with calling kasan_reset_tag() for off-slab
slab management object, leads to freelist being stored non-tagged.

Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
---
 mm/slab.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/mm/slab.c b/mm/slab.c
index c84458281a88..4ad95fcb1686 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -2359,7 +2359,7 @@ static void *alloc_slabmgmt(struct kmem_cache *cachep,
 	void *freelist;
 	void *addr = page_address(page);
 
-	page->s_mem = kasan_reset_tag(addr) + colour_off;
+	page->s_mem = addr + colour_off;
 	page->active = 0;
 
 	if (OBJFREELIST_SLAB(cachep))
@@ -2368,6 +2368,7 @@ static void *alloc_slabmgmt(struct kmem_cache *cachep,
 		/* Slab management obj is off-slab. */
 		freelist = kmem_cache_alloc_node(cachep->freelist_cache,
 					      local_flags, nodeid);
+		freelist = kasan_reset_tag(freelist);
 		if (!freelist)
 			return NULL;
 	} else {
@@ -2681,6 +2682,13 @@ static struct page *cache_grow_begin(struct kmem_cache *cachep,
 
 	offset *= cachep->colour_off;
 
+	/*
+	 * Call kasan_poison_slab() before calling alloc_slabmgmt(), so
+	 * page_address() in the latter returns a non-tagged pointer,
+	 * as it should be for slab pages.
+	 */
+	kasan_poison_slab(page);
+
 	/* Get slab management. */
 	freelist = alloc_slabmgmt(cachep, page, offset,
 			local_flags & ~GFP_CONSTRAINT_MASK, page_node);
@@ -2689,7 +2697,6 @@ static struct page *cache_grow_begin(struct kmem_cache *cachep,
 
 	slab_map_pages(cachep, page, freelist);
 
-	kasan_poison_slab(page);
 	cache_init_objs(cachep, page);
 
 	if (gfpflags_allow_blocking(local_flags))
-- 
2.21.0.rc0.258.g878e2cd30e-goog