linux-kernel - Re: [PATCH] mm/slub: Add check for s->flags in the alloc_tagging_slab_free

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <CAJuCfpEEoq__+yeCXCn0F7HARrVndeEm86sM5XvYeo+UT0cr9g@mail.gmail.com>
Date: Fri, 16 Aug 2024 12:20:53 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: Hao Ge <hao.ge@...ux.dev>
Cc: cl@...ux.com, penberg@...nel.org, rientjes@...gle.com, 
	iamjoonsoo.kim@....com, akpm@...ux-foundation.org, vbabka@...e.cz, 
	roman.gushchin@...ux.dev, 42.hyeyoo@...il.com, kees@...nel.org, 
	kent.overstreet@...ux.dev, linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	Hao Ge <gehao@...inos.cn>
Subject: Re: [PATCH] mm/slub: Add check for s->flags in the alloc_tagging_slab_free_hook

On Thu, Aug 15, 2024 at 6:46 PM Hao Ge <hao.ge@...ux.dev> wrote:
>
> Hi Suren
>
>
> Thank you for taking the time to review this patch.
>
>
> On 8/16/24 05:00, Suren Baghdasaryan wrote:
> > On Thu, Aug 15, 2024 at 12:21 AM Hao Ge <hao.ge@...ux.dev> wrote:
> >> From: Hao Ge <gehao@...inos.cn>
> >>
> >> When enable CONFIG_MEMCG & CONFIG_KFENCE & CONFIG_KMEMLEAK,
> >> the following warning always occurs,This is because the
> >> following call stack occurred:
> >> mem_pool_alloc
> >>      kmem_cache_alloc_noprof
> >>          slab_alloc_node
> >>              kfence_alloc
> >>
> >> Once the kfence allocation is successful,slab->obj_exts will not be empty.
> >> Since in the prepare_slab_obj_exts_hook function,we perform a check for
> >> s->flags & (SLAB_NO_OBJ_EXT | SLAB_NOLEAKTRACE),the alloc_tag_add function
> >> will not be called as a result.Therefore,ref->ct remains NULL.
> >>
> >> However,when we call mem_pool_free,since obj_ext is not empty,
> >> it eventually leads to the alloc_tag_sub scenario being invoked.
> >> This is where the warning occurs.
> > Ok, I was trying to understand why "Once the kfence allocation is
> > successful,slab->obj_exts will not be empty.". alloc_slab_obj_exts()
> > has to be called to create slab->obj_exts. Normally that is done in
> > prepare_slab_obj_exts_hook() which has the s->flags & (SLAB_NO_OBJ_EXT
> > | SLAB_NOLEAKTRACE) check and the cache that kfence_alloc() uses here
> > is the object_cache (passed from mem_pool_alloc()) which has
> > SLAB_NOLEAKTRACE:
> > https://elixir.bootlin.com/linux/v6.11-rc3/source/mm/kmemleak.c#L453.
> > Therefore, prepare_slab_obj_exts_hook() should have skipped it and did
> > not create the slab->obj_exts. So, it must have been called from
> > account_slab() or __memcg_slab_post_alloc_hook() to create
> > slab->obj_exts for memcg accounting in slab->obj_exts.objcg. Ok, now I
> > understand why you need the CONFIG_MEMCG & CONFIG_KFENCE &
> > CONFIG_KMEMLEAK combination.
> > Please confirm that slab->obj_exts creation is happening the way I
> > described above and for those reasons and if so, please update the
> > description of this patch to explain that.
>
> It's mostly correct, but in the context of kfence, the assignment
> actually takes place within the kfence_init_pool function.
>
> https://elixir.bootlin.com/linux/v6.11-rc3/source/mm/kfence/core.c#L606
>
> So in version 2, I have included this explain "because it has already
> been assigned a value in kfence_init_pool."
>
> >> So we should add corresponding checks in the alloc_tagging_slab_free_hook.
> >> For __GFP_NO_OBJ_EXT case,I didn't see the specific case where it's
> >> using kfence,so I won't add the corresponding check in
> >> alloc_tagging_slab_free_hook for now.
> >>
> >> [    3.734349] ------------[ cut here ]------------
> >> [    3.734807] alloc_tag was not set
> >> [    3.735129] WARNING: CPU: 4 PID: 40 at ./include/linux/alloc_tag.h:130 kmem_cache_free+0x444/0x574
> >> [    3.735866] Modules linked in: autofs4
> >> [    3.736211] CPU: 4 UID: 0 PID: 40 Comm: ksoftirqd/4 Tainted: G        W          6.11.0-rc3-dirty #1
> >> [    3.736969] Tainted: [W]=WARN
> >> [    3.737258] Hardware name: QEMU KVM Virtual Machine, BIOS unknown 2/2/2022
> >> [    3.737875] pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> >> [    3.738501] pc : kmem_cache_free+0x444/0x574
> >> [    3.738951] lr : kmem_cache_free+0x444/0x574
> >> [    3.739361] sp : ffff80008357bb60
> >> [    3.739693] x29: ffff80008357bb70 x28: 0000000000000000 x27: 0000000000000000
> >> [    3.740338] x26: ffff80008207f000 x25: ffff000b2eb2fd60 x24: ffff0000c0005700
> >> [    3.740982] x23: ffff8000804229e4 x22: ffff800082080000 x21: ffff800081756000
> >> [    3.741630] x20: fffffd7ff8253360 x19: 00000000000000a8 x18: ffffffffffffffff
> >> [    3.742274] x17: ffff800ab327f000 x16: ffff800083398000 x15: ffff800081756df0
> >> [    3.742919] x14: 0000000000000000 x13: 205d344320202020 x12: 5b5d373038343337
> >> [    3.743560] x11: ffff80008357b650 x10: 000000000000005d x9 : 00000000ffffffd0
> >> [    3.744231] x8 : 7f7f7f7f7f7f7f7f x7 : ffff80008237bad0 x6 : c0000000ffff7fff
> >> [    3.744907] x5 : ffff80008237ba78 x4 : ffff8000820bbad0 x3 : 0000000000000001
> >> [    3.745580] x2 : 68d66547c09f7800 x1 : 68d66547c09f7800 x0 : 0000000000000000
> >> [    3.746255] Call trace:
> >> [    3.746530]  kmem_cache_free+0x444/0x574
> >> [    3.746931]  mem_pool_free+0x44/0xf4
> >> [    3.747306]  free_object_rcu+0xc8/0xdc
> >> [    3.747693]  rcu_do_batch+0x234/0x8a4
> >> [    3.748075]  rcu_core+0x230/0x3e4
> >> [    3.748424]  rcu_core_si+0x14/0x1c
> >> [    3.748780]  handle_softirqs+0x134/0x378
> >> [    3.749189]  run_ksoftirqd+0x70/0x9c
> >> [    3.749560]  smpboot_thread_fn+0x148/0x22c
> >> [    3.749978]  kthread+0x10c/0x118
> >> [    3.750323]  ret_from_fork+0x10/0x20
> >> [    3.750696] ---[ end trace 0000000000000000 ]---
> >>
> >> Fixes: 4b8736964640 ("mm/slab: add allocation accounting into slab allocation and free paths")
> >> Signed-off-by: Hao Ge <gehao@...inos.cn>
> >> ---
> >>   mm/slub.c | 3 +++
> >>   1 file changed, 3 insertions(+)
> >>
> >> diff --git a/mm/slub.c b/mm/slub.c
> >> index c9d8a2497fd6..1f67621ba6dc 100644
> >> --- a/mm/slub.c
> >> +++ b/mm/slub.c
> >> @@ -2116,6 +2116,9 @@ alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p,
> >>          if (!mem_alloc_profiling_enabled())
> >>                  return;
> >>
> >> +       if (s->flags & (SLAB_NO_OBJ_EXT | SLAB_NOLEAKTRACE))
> >> +               return;
> >> +
> > Please add a comment before this check saying something like:
> > /* slab->obj_exts might not be NULL if it was created for MEMCG accounting. */
> >
> > Other than that the fix seems fine to me.
> > Thanks,
> > Suren.
> >
> OK,I have already made the modification in version 2.
> >>          obj_exts = slab_obj_exts(slab);
> >>          if (!obj_exts)
> >>                  return;
> >> --
> >> 2.25.1
> >>
> Thanks

For all fixes to allocation tagging please:

Cc: stable@...r.kernel.org # v6.10

Thanks,
Suren.

>
> best regards
>
> Hao
>