linux-kernel - Re: [PATCH] powerpc/32: Fix missing NULL pmd check in virt_to

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Message-ID: <87zhcfq2n8.fsf@mpe.ellerman.id.au>
Date:   Tue, 17 Mar 2020 10:51:55 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Christophe Leroy <christophe.leroy@....fr>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Nathan Chancellor <natechancellor@...il.com>
Subject: Re: [PATCH] powerpc/32: Fix missing NULL pmd check in virt_to_kpte()

Nick Desaulniers <ndesaulniers@...gle.com> writes:
> Hello ppc friends, did this get picked up into -next yet?

Not yet.

It's in my next-test, but it got stuck there because some subsequent
patches caused some CI errors that I had to debug.

I'll push it to next today.

cheers

> On Thu, Mar 12, 2020 at 8:35 PM Nathan Chancellor
> <natechancellor@...il.com> wrote:
>>
>> On Sat, Mar 07, 2020 at 10:09:15AM +0000, Christophe Leroy wrote:
>> > Commit 2efc7c085f05 ("powerpc/32: drop get_pteptr()"),
>> > replaced get_pteptr() by virt_to_kpte(). But virt_to_kpte() lacks a
>> > NULL pmd check and returns an invalid non NULL pointer when there
>> > is no page table.
>> >
>> > Reported-by: Nick Desaulniers <ndesaulniers@...gle.com>
>> > Fixes: 2efc7c085f05 ("powerpc/32: drop get_pteptr()")
>> > Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
>> > ---
>> >  arch/powerpc/include/asm/pgtable.h | 4 +++-
>> >  1 file changed, 3 insertions(+), 1 deletion(-)
>> >
>> > diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h
>> > index b80bfd41828d..b1f1d5339735 100644
>> > --- a/arch/powerpc/include/asm/pgtable.h
>> > +++ b/arch/powerpc/include/asm/pgtable.h
>> > @@ -54,7 +54,9 @@ static inline pmd_t *pmd_ptr_k(unsigned long va)
>> >
>> >  static inline pte_t *virt_to_kpte(unsigned long vaddr)
>> >  {
>> > -     return pte_offset_kernel(pmd_ptr_k(vaddr), vaddr);
>> > +     pmd_t *pmd = pmd_ptr_k(vaddr);
>> > +
>> > +     return pmd_none(*pmd) ? NULL : pte_offset_kernel(pmd, vaddr);
>> >  }
>> >  #endif
>> >
>> > --
>> > 2.25.0
>> >
>>
>> With QEMU 4.2.0, I can confirm this fixes the panic:
>>
>> Tested-by: Nathan Chancellor <natechancellor@...il.com>
>
>
>
> -- 
> Thanks,
> ~Nick Desaulniers