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Subject: Re: [PATCH 2/2] powerpc/mm: Warn if W+X pages found on boot
To: Russell Currey <ruscur@russell.cc>, linuxppc-dev@lists.ozlabs.org
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From: Christophe Leroy <christophe.leroy@c-s.fr>
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Date: Thu, 2 May 2019 07:23:53 +0200
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Le 01/05/2019 à 09:04, Russell Currey a écrit :
> On Wed, 2019-04-24 at 09:14 +0200, Christophe Leroy wrote:
>>
>> Le 24/04/2019 à 08:39, Russell Currey a écrit :
>>> Implement code to walk all pages and warn if any are found to be
>>> both
>>> writable and executable.  Depends on STRICT_KERNEL_RWX enabled, and
>>> is
>>> behind the DEBUG_WX config option.
>>>
>>> This only runs on boot and has no runtime performance implications.
>>>
>>> Very heavily influenced (and in some cases copied verbatim) from
>>> the
>>> ARM64 code written by Laura Abbott (thanks!), since our ptdump
>>> infrastructure is similar.
>>>
>>> Signed-off-by: Russell Currey <ruscur@russell.cc>
>>> ---
>>>    arch/powerpc/Kconfig.debug         | 19 +++++++++++++++
>>>    arch/powerpc/include/asm/pgtable.h |  5 ++++
>>>    arch/powerpc/mm/pgtable_32.c       |  5 ++++
>>>    arch/powerpc/mm/pgtable_64.c       |  5 ++++
>>>    arch/powerpc/mm/ptdump/ptdump.c    | 38
>>> ++++++++++++++++++++++++++++++
>>>    5 files changed, 72 insertions(+)
>>>
>>> diff --git a/arch/powerpc/Kconfig.debug
>>> b/arch/powerpc/Kconfig.debug
>>> index 4e00cb0a5464..a4160ff02ed4 100644
>>> --- a/arch/powerpc/Kconfig.debug
>>> +++ b/arch/powerpc/Kconfig.debug
>>> @@ -361,6 +361,25 @@ config PPC_PTDUMP
>>>    
>>>    	  If you are unsure, say N.
>>>    
>>> +config DEBUG_WX
>>
>> I would call it PPC_DEBUG_WX to avoid confusion.
> 
> It's the same functionality as on other architectures and is an arch-
> local thing, I personally think it should be left as-is but given we
> already put the PPC prefix on PTDUMP, I'll add it so it's consistent
> 
> <snip>
> 
>>> +	if (radix_enabled())
>>> +		st.start_address = PAGE_OFFSET;
>>> +	else
>> +		st.start_address = KERN_VIRT_START;
>>
>> KERN_VIRT_START doesn't exist on PPC32.
>>
>> Christophe
>>
> Thanks a lot for the review!  Applied all your suggestions.  What
> should I use on PPC32 instead?

Indeed it looks like KERN_VIRT_START is defined as 0 for PPC32 at the 
top of ptdump.c, which look strange to me.

I guess PAGE_OFFSET should be the good value for KERN_VIRT_START on PPC32.

Christophe

> 
> - Russell
>