* [PATCH] mm/slub: do not place freelist pointer to middle of object if redzone is on
@ 2020-04-25 9:13 Changbin Du
2020-04-25 22:48 ` Kees Cook
0 siblings, 1 reply; 5+ messages in thread
From: Changbin Du @ 2020-04-25 9:13 UTC (permalink / raw)
To: Andrew Morton
Cc: Christoph Lameter, Pekka Enberg, David Rientjes, Joonsoo Kim,
Kees Cook, linux-mm, linux-kernel, Changbin Du
The recent kernel fails to boot when slub redzone is turned on. This is
caused by commit 3202fa62fb ("slub: relocate freelist pointer to middle of
object") which relocates freelist pointer to middle of object. In this
case, get_track() gets a wrong address and then the redzone is overwritten.
This patch fixes it by relocating freelist pointer after the object, as
what slub posion does.
[ 2.390256][ T0] =============================================================================
[ 2.392816][ T0] BUG kmem_cache_node (Not tainted): Redzone overwritten
[ 2.393735][ T0] -----------------------------------------------------------------------------
[ 2.393735][ T0]
[ 2.395168][ T0] Disabling lock debugging due to kernel taint
[ 2.395923][ T0] INFO: 0xffff88805c000380-0xffff88805c000387 @offset=896. First byte 0x0 instead of 0xbb
[ 2.397175][ T0] INFO: Slab 0xffffea0001700000 objects=25 used=25 fp=0x0000000000000000 flags=0xfffffc0010200
[ 2.398882][ T0] INFO: Object 0xffff88805c000300 @offset=768 fp=0xffff88805c000580
[ 2.398882][ T0]
[ 2.400145][ T0] Redzone ffff88805c000280: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb ................
[ 2.401593][ T0] Redzone ffff88805c000290: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb ................
[ 2.403825][ T0] Redzone ffff88805c0002a0: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb ................
[ 2.405853][ T0] Redzone ffff88805c0002b0: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb ................
[ 2.407714][ T0] Redzone ffff88805c0002c0: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb ................
[ 2.411066][ T0] Redzone ffff88805c0002d0: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb ................
[ 2.413818][ T0] Redzone ffff88805c0002e0: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb ................
[ 2.415482][ T0] Redzone ffff88805c0002f0: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb ................
[ 2.416975][ T0] Object ffff88805c000300: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
[ 2.418445][ T0] Object ffff88805c000310: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
[ 2.420183][ T0] Object ffff88805c000320: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
[ 2.421911][ T0] Object ffff88805c000330: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
[ 2.423491][ T0] Object ffff88805c000340: 00 00 00 00 00 00 00 00 e8 ed 4a b9 09 7b 20 83 ..........J..{ .
[ 2.425186][ T0] Object ffff88805c000350: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
[ 2.426901][ T0] Object ffff88805c000360: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
[ 2.428673][ T0] Object ffff88805c000370: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
[ 2.430431][ T0] Redzone ffff88805c000380: 00 00 00 00 00 00 00 00 ........
[ 2.485141][ T0] Padding ffff88805c000490: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
[ 2.494198][ T0] Padding ffff88805c0004a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
[ 2.503094][ T0] Padding ffff88805c0004b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
[ 2.578370][ T0] Padding ffff88805c0004c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
[ 2.584420][ T0] Padding ffff88805c0004d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
[ 2.590139][ T0] Padding ffff88805c0004e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
[ 2.596915][ T0] Padding ffff88805c0004f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
[ 2.604002][ T0] CPU: 0 PID: 0 Comm: swapper Tainted: G B 5.7.0-rc1+ #53
[ 2.608493][ T0] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
[ 2.612959][ T0] Call Trace:
[ 2.613953][ T0] dump_stack+0x8c/0xc0
[ 2.615063][ T0] check_bytes_and_report.cold+0x60/0x95
[ 2.616572][ T0] check_object+0x1c1/0x280
[ 2.617462][ T0] ? pvclock_clocksource_read+0xf6/0x1c0
[ 2.618646][ T0] ? __kmem_cache_create+0x16a/0x670
[ 2.619692][ T0] alloc_debug_processing+0x129/0x170
[ 2.620766][ T0] ___slab_alloc+0x58c/0x630
[ 2.621804][ T0] ? __kmem_cache_create+0x16a/0x670
[ 2.622631][ T0] ? print_unlock_imbalance_bug+0x40/0x40
[ 2.623630][ T0] ? lock_acquire+0x11f/0x200
[ 2.624421][ T0] ? __kmem_cache_create+0x16a/0x670
[ 2.625342][ T0] ? __slab_alloc+0x1c/0x30
[ 2.626106][ T0] ? ___slab_alloc+0x5/0x630
[ 2.626890][ T0] __slab_alloc+0x1c/0x30
[ 2.627500][ T0] kmem_cache_alloc_node+0xab/0x2e0
[ 2.628222][ T0] __kmem_cache_create+0x16a/0x670
[ 2.628883][ T0] ? mem_init_print_info+0x2af/0x2be
[ 2.629596][ T0] create_boot_cache+0xa4/0xc8
[ 2.630282][ T0] kmem_cache_init+0x80/0x14a
[ 2.631233][ T0] start_kernel+0x67a/0xa2a
[ 2.631905][ T0] ? thread_stack_cache_init+0x6/0x6
[ 2.632553][ T0] ? x86_family+0x5/0x20
[ 2.633085][ T0] ? load_ucode_bsp+0x50/0x216
[ 2.633629][ T0] secondary_startup_64+0xa4/0xb0
[ 2.634243][ T0] FIX kmem_cache_node: Restoring 0xffff88805c000380-0xffff88805c000387=0xbb
[ 2.634243][ T0]
[ 2.635532][ T0] FIX kmem_cache_node: Marking all objects used
[ 2.636287][ T0] =============================================================================
Fixes: 3202fa62fb ("slub: relocate freelist pointer to middle of object")
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Changbin Du <changbin.du@gmail.com>
---
mm/slub.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/slub.c b/mm/slub.c
index 332d4b459a90..59c5b49038b0 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3570,7 +3570,7 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
*/
s->inuse = size;
- if (((flags & (SLAB_TYPESAFE_BY_RCU | SLAB_POISON)) ||
+ if (((flags & (SLAB_TYPESAFE_BY_RCU | SLAB_RED_ZONE | SLAB_POISON)) ||
s->ctor)) {
/*
* Relocate free pointer after the object if it is not
--
2.25.1
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] mm/slub: do not place freelist pointer to middle of object if redzone is on
2020-04-25 9:13 [PATCH] mm/slub: do not place freelist pointer to middle of object if redzone is on Changbin Du
@ 2020-04-25 22:48 ` Kees Cook
2020-04-26 0:07 ` Changbin Du
0 siblings, 1 reply; 5+ messages in thread
From: Kees Cook @ 2020-04-25 22:48 UTC (permalink / raw)
To: Changbin Du
Cc: Andrew Morton, Christoph Lameter, Pekka Enberg, David Rientjes,
Joonsoo Kim, linux-mm, linux-kernel
On Sat, Apr 25, 2020 at 05:13:38PM +0800, Changbin Du wrote:
> The recent kernel fails to boot when slub redzone is turned on. This is
> caused by commit 3202fa62fb ("slub: relocate freelist pointer to middle of
> object") which relocates freelist pointer to middle of object. In this
> case, get_track() gets a wrong address and then the redzone is overwritten.
Hi! A fix for this is already in -next:
https://www.ozlabs.org/~akpm/mmotm/broken-out/slub-avoid-redzone-when-choosing-freepointer-location.patch
the above doesn't disable the mitigation when using redzones, so I
prefer that to this suggested solution.
--
Kees Cook
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] mm/slub: do not place freelist pointer to middle of object if redzone is on
2020-04-25 22:48 ` Kees Cook
@ 2020-04-26 0:07 ` Changbin Du
0 siblings, 0 replies; 5+ messages in thread
From: Changbin Du @ 2020-04-26 0:07 UTC (permalink / raw)
To: Kees Cook
Cc: Changbin Du, Andrew Morton, Christoph Lameter, Pekka Enberg,
David Rientjes, Joonsoo Kim, linux-mm, linux-kernel
Hi Kees,
On Sat, Apr 25, 2020 at 03:48:31PM -0700, Kees Cook wrote:
> On Sat, Apr 25, 2020 at 05:13:38PM +0800, Changbin Du wrote:
> > The recent kernel fails to boot when slub redzone is turned on. This is
> > caused by commit 3202fa62fb ("slub: relocate freelist pointer to middle of
> > object") which relocates freelist pointer to middle of object. In this
> > case, get_track() gets a wrong address and then the redzone is overwritten.
>
> Hi! A fix for this is already in -next:
>
> https://www.ozlabs.org/~akpm/mmotm/broken-out/slub-avoid-redzone-when-choosing-freepointer-location.patch
>
> the above doesn't disable the mitigation when using redzones, so I
> prefer that to this suggested solution.
>
Glade to see it's been reported. But I am sorry that your patch cannot fix it.
With your fix, I suppose the layout of slub is:
|obj-fp-obj|redzone|track|...
While get_track():
p = object + s->offset + sizeof(void *);
Then we still get a wrong location. I just tested linux-next and the problem is
still there.
Is the right and left redzone good enough to protect the freepointer? If not,
I will send a patch to fix get_track() along with your patch.
> --
> Kees Cook
--
Cheers,
Changbin Du
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] mm/slub: do not place freelist pointer to middle of object if redzone is on
2020-04-25 20:24 Markus Elfring
@ 2020-04-25 23:51 ` Changbin Du
0 siblings, 0 replies; 5+ messages in thread
From: Changbin Du @ 2020-04-25 23:51 UTC (permalink / raw)
To: Markus Elfring
Cc: Changbin Du, Andrew Morton, linux-mm, linux-kernel,
Christoph Lameter, David Rientjes, Joonsoo Kim, Kees Cook,
Pekka Enberg
On Sat, Apr 25, 2020 at 10:24:45PM +0200, Markus Elfring wrote:
> > Fixes: 3202fa62fb ("slub: relocate freelist pointer to middle of object")
>
> Will a longer commit identifier be safer for the final change description?
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst?id=b2768df24ec400dd4f7fa79542f797e904812053#n183
>
I used to give 12 charactors, but this time I lost two. :)
> Regards,
> Markus
--
Cheers,
Changbin Du
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] mm/slub: do not place freelist pointer to middle of object if redzone is on
@ 2020-04-25 20:24 Markus Elfring
2020-04-25 23:51 ` Changbin Du
0 siblings, 1 reply; 5+ messages in thread
From: Markus Elfring @ 2020-04-25 20:24 UTC (permalink / raw)
To: Changbin Du, Andrew Morton, linux-mm
Cc: linux-kernel, Christoph Lameter, David Rientjes, Joonsoo Kim,
Kees Cook, Pekka Enberg
> Fixes: 3202fa62fb ("slub: relocate freelist pointer to middle of object")
Will a longer commit identifier be safer for the final change description?
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst?id=b2768df24ec400dd4f7fa79542f797e904812053#n183
Regards,
Markus
^ permalink raw reply [flat|nested] 5+ messages in thread
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2020-04-25 9:13 [PATCH] mm/slub: do not place freelist pointer to middle of object if redzone is on Changbin Du
2020-04-25 22:48 ` Kees Cook
2020-04-26 0:07 ` Changbin Du
2020-04-25 20:24 Markus Elfring
2020-04-25 23:51 ` Changbin Du
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