linux-kernel - Re: [RFC][PATCH 5/6] x86, efi: Fix endian issues and unaligned accesses

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Message-Id: <20120229105210.312c6a8f8115659d41337518@canb.auug.org.au>
Date:	Wed, 29 Feb 2012 10:52:10 +1100
From:	Stephen Rothwell <sfr@...b.auug.org.au>
To:	Matt Fleming <matt@...sole-pimps.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Matt Fleming <matt.fleming@...el.com>,
	Nick Bowler <nbowler@...iptictech.com>
Subject: Re: [RFC][PATCH 5/6] x86, efi: Fix endian issues and unaligned
 accesses

Hi all,

On Tue, 28 Feb 2012 13:37:24 +0000 Matt Fleming <matt@...sole-pimps.org> wrote:
>
> From: Matt Fleming <matt.fleming@...el.com>
> 
> We may need to convert the endianness of the data we read from/write
> to 'buf', so let's use {get,put}_unaligned_le32() to do that. Failure
> to do so can result in accessing invalid memory, leading to a
> segfault.  Stephen Rothwell noticed this bug while cross-building an
> x86_64 allmodconfig kernel on PowerPC.
> 
> We need to read from and write to 'buf' a byte at a time otherwise
> it's possible we'll perform an unaligned access, which can lead to bus
> errors when cross-building an x86 kernel on risc architectures.
> 
> Cc: H. Peter Anvin <hpa@...or.com>
> Cc: Nick Bowler <nbowler@...iptictech.com>
> Tested-by: Stephen Rothwell <sfr@...b.auug.org.au>
> Reported-by: Stephen Rothwell <sfr@...b.auug.org.au>
> Signed-off-by: Matt Fleming <matt.fleming@...el.com>

Just to be absolutely clear, I have not yet tested this version of the
patch and also this fixes a problem with cross building Linus' tree (i.e.
this is a regression with cross building introduced in v3.3-rc1).

-- 
Cheers,
Stephen Rothwell                    sfr@...b.auug.org.au
http://www.canb.auug.org.au/~sfr/

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