[v2] page_poison: play nicely with KASAN
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Message ID 20190114233405.67843-1-cai@lca.pw
State New
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Series
  • [v2] page_poison: play nicely with KASAN
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Commit Message

Qian Cai Jan. 14, 2019, 11:34 p.m. UTC
KASAN does not play well with the page poisoning
(CONFIG_PAGE_POISONING). It triggers false positives in the allocation
path,

BUG: KASAN: use-after-free in memchr_inv+0x2ea/0x330
Read of size 8 at addr ffff88881f800000 by task swapper/0
CPU: 0 PID: 0 Comm: swapper Not tainted 5.0.0-rc1+ #54
Call Trace:
 dump_stack+0xe0/0x19a
 print_address_description.cold.2+0x9/0x28b
 kasan_report.cold.3+0x7a/0xb5
 __asan_report_load8_noabort+0x19/0x20
 memchr_inv+0x2ea/0x330
 kernel_poison_pages+0x103/0x3d5
 get_page_from_freelist+0x15e7/0x4d90

because KASAN has not yet unpoisoned the shadow page for allocation
before it checks memchr_inv() but only found a stale poison pattern.

Also, false positives in free path,

BUG: KASAN: slab-out-of-bounds in kernel_poison_pages+0x29e/0x3d5
Write of size 4096 at addr ffff8888112cc000 by task swapper/0/1
CPU: 5 PID: 1 Comm: swapper/0 Not tainted 5.0.0-rc1+ #55
Call Trace:
 dump_stack+0xe0/0x19a
 print_address_description.cold.2+0x9/0x28b
 kasan_report.cold.3+0x7a/0xb5
 check_memory_region+0x22d/0x250
 memset+0x28/0x40
 kernel_poison_pages+0x29e/0x3d5
 __free_pages_ok+0x75f/0x13e0

due to KASAN adds poisoned redzones around slab objects, but the page
poisoning needs to poison the whole page.

Signed-off-by: Qian Cai <cai@lca.pw>
---

v2: use kasan_disable/enable_current() instead.

 mm/page_alloc.c  | 2 +-
 mm/page_poison.c | 4 ++++
 2 files changed, 5 insertions(+), 1 deletion(-)

Comments

Andrey Ryabinin Jan. 15, 2019, 5:25 p.m. UTC | #1
On 1/15/19 2:34 AM, Qian Cai wrote:
> KASAN does not play well with the page poisoning
> (CONFIG_PAGE_POISONING). It triggers false positives in the allocation
> path,
> 
> BUG: KASAN: use-after-free in memchr_inv+0x2ea/0x330
> Read of size 8 at addr ffff88881f800000 by task swapper/0
> CPU: 0 PID: 0 Comm: swapper Not tainted 5.0.0-rc1+ #54
> Call Trace:
>  dump_stack+0xe0/0x19a
>  print_address_description.cold.2+0x9/0x28b
>  kasan_report.cold.3+0x7a/0xb5
>  __asan_report_load8_noabort+0x19/0x20
>  memchr_inv+0x2ea/0x330
>  kernel_poison_pages+0x103/0x3d5
>  get_page_from_freelist+0x15e7/0x4d90
> 
> because KASAN has not yet unpoisoned the shadow page for allocation
> before it checks memchr_inv() but only found a stale poison pattern.
> 
> Also, false positives in free path,
> 
> BUG: KASAN: slab-out-of-bounds in kernel_poison_pages+0x29e/0x3d5
> Write of size 4096 at addr ffff8888112cc000 by task swapper/0/1
> CPU: 5 PID: 1 Comm: swapper/0 Not tainted 5.0.0-rc1+ #55
> Call Trace:
>  dump_stack+0xe0/0x19a
>  print_address_description.cold.2+0x9/0x28b
>  kasan_report.cold.3+0x7a/0xb5
>  check_memory_region+0x22d/0x250
>  memset+0x28/0x40
>  kernel_poison_pages+0x29e/0x3d5
>  __free_pages_ok+0x75f/0x13e0
> 
> due to KASAN adds poisoned redzones around slab objects, but the page
> poisoning needs to poison the whole page.
> 
> Signed-off-by: Qian Cai <cai@lca.pw>
> ---
> 
Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com>

Patch
diff mbox series

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d295c9bc01a8..906250a9b89c 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1945,8 +1945,8 @@  inline void post_alloc_hook(struct page *page, unsigned int order,
 
 	arch_alloc_page(page, order);
 	kernel_map_pages(page, 1 << order, 1);
-	kernel_poison_pages(page, 1 << order, 1);
 	kasan_alloc_pages(page, order);
+	kernel_poison_pages(page, 1 << order, 1);
 	set_page_owner(page, order, gfp_flags);
 }
 
diff --git a/mm/page_poison.c b/mm/page_poison.c
index f0c15e9017c0..21d4f97cb49b 100644
--- a/mm/page_poison.c
+++ b/mm/page_poison.c
@@ -6,6 +6,7 @@ 
 #include <linux/page_ext.h>
 #include <linux/poison.h>
 #include <linux/ratelimit.h>
+#include <linux/kasan.h>
 
 static bool want_page_poisoning __read_mostly;
 
@@ -40,7 +41,10 @@  static void poison_page(struct page *page)
 {
 	void *addr = kmap_atomic(page);
 
+	/* KASAN still think the page is in-use, so skip it. */
+	kasan_disable_current();
 	memset(addr, PAGE_POISON, PAGE_SIZE);
+	kasan_enable_current();
 	kunmap_atomic(addr);
 }