Message-ID: <CAJuCfpHRqttunq=TTWnmcOO1vNU9g-5UxbtS_T44Ef4NB3XaRw@mail.gmail.com>
Date: Sat, 19 Oct 2024 14:17:35 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: Hao Ge <hao.ge@...ux.dev>
Cc: kent.overstreet@...ux.dev, akpm@...ux-foundation.org, yuzhao@...gle.com, 
	linux-mm@...ck.org, linux-kernel@...r.kernel.org, Hao Ge <gehao@...inos.cn>
Subject: Re: [PATCH v2] mm/codetag: move ref and tag null pointer check to alloc_tag_add

On Fri, Oct 18, 2024 at 5:47 PM Hao Ge <hao.ge@...ux.dev> wrote:
>
> Hi Suren
>
>
> On 10/19/24 01:30, Suren Baghdasaryan wrote:
> > On Fri, Oct 18, 2024 at 9:26 AM Hao Ge <hao.ge@...ux.dev> wrote:
> >> From: Hao Ge <gehao@...inos.cn>
> >>
> >> When we compile and load lib/slub_kunit.c,it will cause a panic.
> >>
> >> The root cause is that __kmalloc_cache_noprof was directly called
> >> instead of kmem_cache_alloc,which resulted in no alloc_tag being
> >> allocated.This caused current->alloc_tag to be null,leading to a
> >> null pointer dereference in alloc_tag_ref_set.
> >>
> >> Despite the fact that my colleague Pei Xiao will later fix the code
> >> in slub_kunit.c,we still need to move the null pointer check for ref
> >> and tag to alloc_tag_add here.
> >> It is sufficient for us to issue a warning to the user;
> >> It should not lead to a panic.
> >>
> >> Here is the log for the panic:
> >>
> >> [   74.779373][ T2158] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000020
> >> [   74.780130][ T2158] Mem abort info:
> >> [   74.780406][ T2158]   ESR = 0x0000000096000004
> >> [   74.780756][ T2158]   EC = 0x25: DABT (current EL), IL = 32 bits
> >> [   74.781225][ T2158]   SET = 0, FnV = 0
> >> [   74.781529][ T2158]   EA = 0, S1PTW = 0
> >> [   74.781836][ T2158]   FSC = 0x04: level 0 translation fault
> >> [   74.782288][ T2158] Data abort info:
> >> [   74.782577][ T2158]   ISV = 0, ISS = 0x00000004, ISS2 = 0x00000000
> >> [   74.783068][ T2158]   CM = 0, WnR = 0, TnD = 0, TagAccess = 0
> >> [   74.783533][ T2158]   GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
> >> [   74.784010][ T2158] user pgtable: 4k pages, 48-bit VAs, pgdp=0000000105f34000
> >> [   74.784586][ T2158] [0000000000000020] pgd=0000000000000000, p4d=0000000000000000
> >> [   74.785293][ T2158] Internal error: Oops: 0000000096000004 [#1] SMP
> >> [   74.785805][ T2158] Modules linked in: slub_kunit kunit ip6t_rpfilter ip6t_REJECT nf_reject_ipv6 ipt_REJECT nf_reject_ipv4 xt_conntrack ebtable_nat ebtable_broute ip6table_nat ip6table_mangle 4
> >> [   74.790661][ T2158] CPU: 0 UID: 0 PID: 2158 Comm: kunit_try_catch Kdump: loaded Tainted: G        W        N 6.12.0-rc3+ #2
> >> [   74.791535][ T2158] Tainted: [W]=WARN, [N]=TEST
> >> [   74.791889][ T2158] Hardware name: QEMU KVM Virtual Machine, BIOS 0.0.0 02/06/2015
> >> [   74.792479][ T2158] pstate: 40400005 (nZcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> >> [   74.793101][ T2158] pc : alloc_tagging_slab_alloc_hook+0x120/0x270
> >> [   74.793607][ T2158] lr : alloc_tagging_slab_alloc_hook+0x120/0x270
> >> [   74.794095][ T2158] sp : ffff800084d33cd0
> >> [   74.794418][ T2158] x29: ffff800084d33cd0 x28: 0000000000000000 x27: 0000000000000000
> >> [   74.795095][ T2158] x26: 0000000000000000 x25: 0000000000000012 x24: ffff80007b30e314
> >> [   74.795822][ T2158] x23: ffff000390ff6f10 x22: 0000000000000000 x21: 0000000000000088
> >> [   74.796555][ T2158] x20: ffff000390285840 x19: fffffd7fc3ef7830 x18: ffffffffffffffff
> >> [   74.797283][ T2158] x17: ffff8000800e63b4 x16: ffff80007b33afc4 x15: ffff800081654c00
> >> [   74.798011][ T2158] x14: 0000000000000000 x13: 205d383531325420 x12: 5b5d383734363537
> >> [   74.798744][ T2158] x11: ffff800084d337e0 x10: 000000000000005d x9 : 00000000ffffffd0
> >> [   74.799476][ T2158] x8 : 7f7f7f7f7f7f7f7f x7 : ffff80008219d188 x6 : c0000000ffff7fff
> >> [   74.800206][ T2158] x5 : ffff0003fdbc9208 x4 : ffff800081edd188 x3 : 0000000000000001
> >> [   74.800932][ T2158] x2 : 0beaa6dee1ac5a00 x1 : 0beaa6dee1ac5a00 x0 : ffff80037c2cb000
> >> [   74.801656][ T2158] Call trace:
> >> [   74.801954][ T2158]  alloc_tagging_slab_alloc_hook+0x120/0x270
> >> [   74.802494][ T2158]  __kmalloc_cache_noprof+0x148/0x33c
> >> [   74.802976][ T2158]  test_kmalloc_redzone_access+0x4c/0x104 [slub_kunit]
> >> [   74.803607][ T2158]  kunit_try_run_case+0x70/0x17c [kunit]
> >> [   74.804124][ T2158]  kunit_generic_run_threadfn_adapter+0x2c/0x4c [kunit]
> >> [   74.804768][ T2158]  kthread+0x10c/0x118
> >> [   74.805141][ T2158]  ret_from_fork+0x10/0x20
> >> [   74.805540][ T2158] Code: b9400a80 11000400 b9000a80 97ffd858 (f94012d3)
> >> [   74.806176][ T2158] SMP: stopping secondary CPUs
> >> [   74.808130][ T2158] Starting crashdump kernel...
> >>
> >> Fixes: e0a955bf7f61 ("mm/codetag: add pgalloc_tag_copy()")
> >> Signed-off-by: Hao Ge <gehao@...inos.cn>
> >> ---
> >> v2: Modify the errors in the title and commit message.
> >>      Remove the empty lines that were mistakenly added in version v1.
> >> ---
> >>   include/linux/alloc_tag.h | 8 ++++----
> >>   1 file changed, 4 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/include/linux/alloc_tag.h b/include/linux/alloc_tag.h
> >> index 1f0a9ff23a2c..8603e3a9df10 100644
> >> --- a/include/linux/alloc_tag.h
> >> +++ b/include/linux/alloc_tag.h
> >> @@ -137,10 +137,6 @@ static inline void alloc_tag_sub_check(union codetag_ref *ref) {}
> >>   /* Caller should verify both ref and tag to be valid */
> >>   static inline void __alloc_tag_ref_set(union codetag_ref *ref, struct alloc_tag *tag)
> >>   {
> >> -       alloc_tag_add_check(ref, tag);
> >> -       if (!ref || !tag)
> >> -               return;
> >> -
> > Unfortunately this change will result in __alloc_tag_ref_set() and
> > alloc_tag_ref_set() missing the following important check from
> > alloc_tag_sub_check():
> >
>
> Maybe I missed something here, I'm a bit confused. Can you give me an
> example to explain it?

Sure. The warning I indicated would trigger when (ref != NULL &&
ref->ct != NULL), which means that we have a valid tag reference and
it's pointing to a valid tag. During allocation that is abnormal
because we expect that if the reference is valid (ref != NULL), it
should have been cleared (ref->ct == NULL). With your change we won't
get these warnings when calling __alloc_tag_ref_set() and
alloc_tag_ref_set(). Does that make sense?

>
> Thanks
>
>
> Best regards
> Hao
>
>
> > WARN_ONCE(ref && ref->ct,
> >    "alloc_tag was not cleared (got tag for %s:%u)\n",
> >    ref->ct->filename, ref->ct->lineno);
> >
> > I think the change below would fix this issue without the above
> > mentioned side-effect:
> >
> > -static inline void __alloc_tag_ref_set(union codetag_ref *ref, struct
> > alloc_tag *tag)
> > +static inline bool __alloc_tag_ref_set(union codetag_ref *ref, struct
> > alloc_tag *tag)
> >   {
> >          alloc_tag_add_check(ref, tag);
> >          if (!ref || !tag)
> > -                return;
> > +                return false;
> >
> >          ref->ct = &tag->ct;
> > +        return true;
> >   }
> >
> > -static inline void alloc_tag_ref_set(union codetag_ref *ref, struct
> > alloc_tag *tag)
> > +static inline bool alloc_tag_ref_set(union codetag_ref *ref, struct
> > alloc_tag *tag)
> >   {
> > -        __alloc_tag_ref_set(ref, tag);
> > +        if (unlikely(!__alloc_tag_ref_set(ref, tag)))
> > +                return false;
> > +
> >          /*
> >           * We need in increment the call counter every time we have a new
> >           * allocation or when we split a large allocation into smaller ones.
> >           * Each new reference for every sub-allocation needs to increment call
> >           * counter because when we free each part the counter will be
> > decremented.
> >           */
> >          this_cpu_inc(tag->counters->calls);
> > +        return true;
> >   }
> >
> >   static inline void alloc_tag_add(union codetag_ref *ref, struct
> > alloc_tag *tag, size_t bytes)
> >   {
> > -        alloc_tag_ref_set(ref, tag);
> > -        this_cpu_add(tag->counters->bytes, bytes);
> > +        if (likely(alloc_tag_ref_set(ref, tag)))
> > +                this_cpu_add(tag->counters->bytes, bytes);
> >   }
> >
> > Could you please confirm this fix?
> > Thanks,
> > Suren.
> >
> >>          ref->ct = &tag->ct;
> >>   }
> >>
> >> @@ -158,6 +154,10 @@ static inline void alloc_tag_ref_set(union codetag_ref *ref, struct alloc_tag *t
> >>
> >>   static inline void alloc_tag_add(union codetag_ref *ref, struct alloc_tag *tag, size_t bytes)
> >>   {
> >> +       alloc_tag_add_check(ref, tag);
> >> +       if (!ref || !tag)
> >> +               return;
> >> +
> >>          alloc_tag_ref_set(ref, tag);
> >>          this_cpu_add(tag->counters->bytes, bytes);
> >>   }
> >> --
> >> 2.25.1
> >>

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