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Subject: Re: BUG: memcmp(): Accessing invalid memory location
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
 Chandan Rajendra <chandan@linux.ibm.com>, linuxppc-dev@lists.ozlabs.org
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From: Christophe Leroy <christophe.leroy@c-s.fr>
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Date: Fri, 25 Jan 2019 07:45:14 +0100
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Cc: Anton Blanchard <anton@au1.ibm.com>, Nick Piggin <npiggin@au1.ibm.com>,
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Le 25/01/2019 à 01:55, Benjamin Herrenschmidt a écrit :
> On Thu, 2019-01-24 at 19:48 +0530, Chandan Rajendra wrote:
>> - Here we execute "LD rB,0,r4". In the case of this bug, r4 has an unaligned
>>    value and hence ends up accessing the "next" double word. The "next" double
>>    word happens to occur after the last page mapped into the kernel's address
>>    space and hence this leads to the previously listed oops.
>>    
> 
> This is interesting ... should we mark the last page of any piece of
> mapped linear mapping as reserved to avoid that sort of issue ?

Or revert to a normal comparison once remaining length is < 8 and r4 in 
unaligned ?

Christophe

> 
> Nick ? Aneesh ?
> 
> Cheers,
> Ben.
>