linux-kernel - Re: [PATCH v7 7/9] mm: Add address parameter to arch_validate

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Date:   Tue, 15 Aug 2017 15:02:08 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Khalid Aziz <khalid.aziz@...cle.com>, akpm@...ux-foundation.org,
        benh@...nel.crashing.org, paulus@...ba.org, davem@...emloft.net,
        dave.hansen@...ux.intel.com
Cc:     bsingharora@...il.com, dja@...ens.net, tglx@...utronix.de,
        mgorman@...e.de, aarcange@...hat.com,
        kirill.shutemov@...ux.intel.com, heiko.carstens@...ibm.com,
        ak@...ux.intel.com, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        sparclinux@...r.kernel.org, Khalid Aziz <khalid@...ehiking.org>
Subject: Re: [PATCH v7 7/9] mm: Add address parameter to arch_validate_prot()

Khalid Aziz <khalid.aziz@...cle.com> writes:

> On 08/10/2017 07:20 AM, Michael Ellerman wrote:
>> Khalid Aziz <khalid.aziz@...cle.com> writes:
>> 
>>> A protection flag may not be valid across entire address space and
>>> hence arch_validate_prot() might need the address a protection bit is
>>> being set on to ensure it is a valid protection flag. For example, sparc
>>> processors support memory corruption detection (as part of ADI feature)
>>> flag on memory addresses mapped on to physical RAM but not on PFN mapped
>>> pages or addresses mapped on to devices. This patch adds address to the
>>> parameters being passed to arch_validate_prot() so protection bits can
>>> be validated in the relevant context.
>>>
>>> Signed-off-by: Khalid Aziz <khalid.aziz@...cle.com>
>>> Cc: Khalid Aziz <khalid@...ehiking.org>
>>> ---
>>> v7:
>>> 	- new patch
>>>
>>>   arch/powerpc/include/asm/mman.h | 2 +-
>>>   arch/powerpc/kernel/syscalls.c  | 2 +-
>>>   include/linux/mman.h            | 2 +-
>>>   mm/mprotect.c                   | 2 +-
>>>   4 files changed, 4 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/arch/powerpc/include/asm/mman.h b/arch/powerpc/include/asm/mman.h
>>> index 30922f699341..bc74074304a2 100644
>>> --- a/arch/powerpc/include/asm/mman.h
>>> +++ b/arch/powerpc/include/asm/mman.h
>>> @@ -40,7 +40,7 @@ static inline bool arch_validate_prot(unsigned long prot)
>>>   		return false;
>>>   	return true;
>>>   }
>>> -#define arch_validate_prot(prot) arch_validate_prot(prot)
>>> +#define arch_validate_prot(prot, addr) arch_validate_prot(prot)
>> 
>> This can be simpler, as just:
>> 
>> #define arch_validate_prot arch_validate_prot
>> 
>
> Hi Michael,
>
> Thanks for reviewing!
>
> My patch expands parameter list for arch_validate_prot() from one to two 
> parameters. Existing powerpc version of arch_validate_prot() is written 
> with one parameter. If I use the above #define, compilation fails with:
>
> mm/mprotect.c: In function ‘do_mprotect_pkey’:
> mm/mprotect.c:399: error: too many arguments to function 
> ‘arch_validate_prot’
>
> Another way to solve it would be to add the new addr parameter to 
> powerpc version of arch_validate_prot() but I chose the less disruptive 
> solution of tackling it through #define and expanded the existing 
> #define to include the new parameter. Make sense?

Yes, it makes sense. But it's a bit gross.

At first glance it looks like our arch_validate_prot() has an incorrect
signature.

I'd prefer you just updated it to have the correct signature, I think
you'll have to change one more line in do_mmap2(). So it's not very
intrusive.

cheers