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Date: Thu, 7 Feb 2019 06:52:56 -0600
From: Segher Boessenkool <segher@kernel.crashing.org>
To: Michael Ellerman <mpe@ellerman.id.au>
Subject: Re: [PATCH v2] powerpc/64: Fix memcmp reading past the end of src/dest
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Cc: linuxppc-dev@ozlabs.org, chandan@linux.ibm.com, npiggin@gmail.com,
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On Thu, Feb 07, 2019 at 10:53:13PM +1100, Michael Ellerman wrote:
> Chandan reported that fstests' generic/026 test hit a crash:

> The instruction dump decodes as:
>   subfic  r6,r5,8
>   rlwinm  r6,r6,3,0,28
>   ldbrx   r9,0,r3
>   ldbrx   r10,0,r4	<-
> 
> Which shows us doing an 8 byte load from c00000062ac3fff9, which
> crosses the page boundary at c00000062ac40000 and faults.
> 
> It's not OK for memcmp to read past the end of the source or
> destination buffers.

It's not okay to access memory pages unsolicited.  Reading past the end
is fine per se.


Segher