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Date: Tue, 6 Apr 2010 10:51:44 -0400
Message-ID: <g2g817ecb6f1004060751s1fd3d42bqc19b5c36b33c3c13@mail.gmail.com>
Subject: Re: [PATCH 1/4] [tip:x86/mm] Correcting improper large page 
	preservation
From: Siarhei Liakh <sliakh.lkml@gmail.com>
To: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       "linux-security-module@vger.kernel.org" 
	<linux-security-module@vger.kernel.org>,
       "linux-next@vger.kernel.org" <linux-next@vger.kernel.org>,
       Arjan van de Ven <arjan@infradead.org>,
       James Morris <jmorris@namei.org>,
       Andrew Morton <akpm@linux-foundation.org>, Andi Kleen <ak@muc.de>,
       Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>,
       Ingo Molnar <mingo@elte.hu>, Rusty Russell <rusty@rustcorp.com.au>,
       Stephen Rothwell <sfr@canb.auug.org.au>, Dave Jones <davej@redhat.com>
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On Sat, Apr 3, 2010 at 2:43 AM, Suresh Siddha <suresh.b.siddha@intel.com> wrote:
> On Wed, 2010-03-31 at 18:59 -0700, Siarhei Liakh wrote:
>> +     /*
>> +      * .data and .bss should always be writable.
>> +      */
>> +     if ((within(pfn, __pa((unsigned long)_sdata) >> PAGE_SHIFT,
>> +                __pa((unsigned long)_edata) >> PAGE_SHIFT)) ||
>> +         (within(pfn, __pa((unsigned long)__bss_start) >> PAGE_SHIFT,
>> +                __pa((unsigned long)__bss_stop) >> PAGE_SHIFT))) {
>> +             pgprot_val(required) |= _PAGE_RW;
>> +     }
>
> I have reviewed this patch and the only comment I have is:
>
> On 64bit kernels, kernel text/data mapping and kernel identity mappings
> are different virtual addresses mapping to same pfn ranges. For the
> data/bss pages, does it help (in identifying certain data corruptions
> more easily) in making the kernel identity mapping to be set to
> read-only and enforce the need of RW only for the kernel data mappings.
>
> Or is there some obscure code that uses something like
> __va(__pa(data_symbol)) and writes to it?
>
> If not, we can remove the __pa() constructs above and use the addr for
> comparisons.

Done.
Patch V2 have been posted.