From: Nicolas Bouchinet <nicolas.bouchinet@clip-os.org>
To: Xiongwei Song <sxwjean@gmail.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, cl@linux.com,
penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com,
akpm@linux-foundation.org, vbabka@suse.cz,
roman.gushchin@linux.dev, 42.hyeyoo@gmail.com
Subject: Re: [PATCH] slub: Fixes freepointer encoding for single free
Date: Fri, 26 Apr 2024 14:18:56 +0200 [thread overview]
Message-ID: <47011bf2-4000-4fd8-9dd3-4c6b6a1c4a80@clip-os.org> (raw)
In-Reply-To: <CAEVVKH8Oagbih8E8YNPpNhyh75fWnBLdod+eEGQm9i8ciNv7sQ@mail.gmail.com>
On 4/26/24 11:20, Xiongwei Song wrote:
> On Wed, Apr 24, 2024 at 8:48 PM Nicolas Bouchinet
> <nicolas.bouchinet@clip-os.org> wrote:
>> From: Nicolas Bouchinet <nicolas.bouchinet@ssi.gouv.fr>
>>
>> Commit 284f17ac13fe ("mm/slub: handle bulk and single object freeing
>> separately") splits single and bulk object freeing in two functions
>> slab_free() and slab_free_bulk() which leads slab_free() to call
>> slab_free_hook() directly instead of slab_free_freelist_hook().
>>
>> If `init_on_free` is set, slab_free_hook() zeroes the object.
>> Afterward, if `slub_debug=F` and `CONFIG_SLAB_FREELIST_HARDENED` are
>> set, the do_slab_free() slowpath executes freelist consistency
>> checks and try to decode a zeroed freepointer which leads to a
>> "Freepointer corrupt" detection in check_object().
>>
>> Object's freepointer thus needs to be properly set using
>> set_freepointer() after init_on_free.
>>
>> To reproduce, set `slub_debug=FU init_on_free=1 log_level=7` on the
>> command line of a kernel build with `CONFIG_SLAB_FREELIST_HARDENED=y`.
>>
>> dmesg sample log:
>> [ 10.708715] =============================================================================
>> [ 10.710323] BUG kmalloc-rnd-05-32 (Tainted: G B T ): Freepointer corrupt
>> [ 10.712695] -----------------------------------------------------------------------------
>> [ 10.712695]
>> [ 10.712695] Slab 0xffffd8bdc400d580 objects=32 used=4 fp=0xffff9d9a80356f80 flags=0x200000000000a00(workingset|slab|node=0|zone=2)
>> [ 10.716698] Object 0xffff9d9a80356600 @offset=1536 fp=0x7ee4f480ce0ecd7c
> If init_on_free is set, slab_free_hook() zeros the object first, then
> do_slab_free() calls
> set_freepointer() to set the fp value, so there are 8 bytes non-zero
> at the moment?
> Hence, the issue is not related to init_on_free?
>
> The fp=0x7ee4f480ce0ecd7c here is beyond kernel memory space, is the issue from
> CONFIG_SLAB_FREELIST_HARDENED enabled?
My understanding of the bug is that slab_free_hook() indeed zeroes the
object and its metadata first, then calls do_slab_free() and directly
calls __slab_free(), head an tail parameters being set to the object.
If `slub_debug=F` (SLAB_CONSISTENCY_CHECKS) is set, the following call
path can be executed :
free_to_partial_list() ->
free_debug_processing() ->
free_consistency_checks() ->
check_object() ->
check_valid_pointer(get_freepointer())
When check_valid_pointer() is called, its object parameter is first
decoded by get_freepointer(), if CONFIG_SLAB_FREELIST_HARDENED is
enabled, zeroed data is then decoded by freelist_ptr_decode() using the
(ptr.v ^ s->random ^ swab(ptr_addr)) operation.
Does that makes sense to you or do you think I'm missing something ?
Best regards,
Nicolas
> Xiongwei
>
>> [ 10.716698]
>> [ 10.716698] Bytes b4 ffff9d9a803565f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
>> [ 10.720703] Object ffff9d9a80356600: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
>> [ 10.720703] Object ffff9d9a80356610: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
>> [ 10.724696] Padding ffff9d9a8035666c: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
>> [ 10.724696] Padding ffff9d9a8035667c: 00 00 00 00 ....
>> [ 10.724696] FIX kmalloc-rnd-05-32: Object at 0xffff9d9a80356600 not freed
>>
>> Signed-off-by: Nicolas Bouchinet <nicolas.bouchinet@ssi.gouv.fr>
>> ---
>> mm/slub.c | 8 +++++++-
>> 1 file changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/slub.c b/mm/slub.c
>> index 3aa12b9b323d9..71dbff9ad8f17 100644
>> --- a/mm/slub.c
>> +++ b/mm/slub.c
>> @@ -4342,10 +4342,16 @@ static __fastpath_inline
>> void slab_free(struct kmem_cache *s, struct slab *slab, void *object,
>> unsigned long addr)
>> {
>> + bool init = false;
>> +
>> memcg_slab_free_hook(s, slab, &object, 1);
>> + init = slab_want_init_on_free(s);
>>
>> - if (likely(slab_free_hook(s, object, slab_want_init_on_free(s))))
>> + if (likely(slab_free_hook(s, object, init))) {
>> + if (init)
>> + set_freepointer(s, object, NULL);
>> do_slab_free(s, slab, object, object, 1, addr);
>> + }
>> }
>>
>> static __fastpath_inline
>> --
>> 2.44.0
>>
>>
next prev parent reply other threads:[~2024-04-26 12:19 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-24 12:47 [PATCH] slub: Fixes freepointer encoding for single free Nicolas Bouchinet
2024-04-25 8:36 ` Chengming Zhou
2024-04-25 15:02 ` Nicolas Bouchinet
2024-04-25 15:14 ` Chengming Zhou
2024-04-29 8:52 ` Vlastimil Babka
2024-04-29 9:09 ` Nicolas Bouchinet
2024-04-29 12:59 ` Nicolas Bouchinet
2024-04-29 13:35 ` Chengming Zhou
2024-04-29 14:32 ` Nicolas Bouchinet
2024-04-29 14:52 ` Chengming Zhou
2024-04-29 16:16 ` Nicolas Bouchinet
2024-04-29 20:22 ` Vlastimil Babka
2024-04-30 9:19 ` Nicolas Bouchinet
2024-04-26 9:20 ` Xiongwei Song
2024-04-26 12:18 ` Nicolas Bouchinet [this message]
2024-04-26 13:14 ` Xiongwei Song
2024-04-29 7:55 ` Nicolas Bouchinet
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