linux-kernel - [PATCH] hexdump: fix for non-naturally-aligned buffers

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Date:	Sun, 21 Jun 2015 18:36:57 +0200
From:	=?UTF-8?q?Horacio=20Mijail=20Ant=C3=B3n=20Quiles?= <hmijail@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	David Howells <dhowells@...hat.com>,
	Vivek Goyal <vgoyal@...hat.com>, linux-kernel@...r.kernel.org,
	trivial@...nel.org
Subject: [PATCH] hexdump: fix for non-naturally-aligned buffers

Calling hex_dump_to_buffer() with a buffer non-naturally-aligned to the
groupsize causes non-naturally-aligned memory accesses. This was causing
a kernel panic on the BlackFin BF527, when such a call was made by 
ubifs_scanned_corruption() in fs/ubifs/scan.c .

To fix this, if the buffer is non-naturally aligned in a platform which 
does not define CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS, then change the
groupsize to 1, so alignment is no longer a problem.
This behavior is coherent with the way the function currently deals with
inappropriate parameter combinations, which is to fall back to safe
"defaults", even if that means changing the output format and the implicit
access patterns that could have been expected.

Signed-off-by: Horacio Mijail Antón Quiles <hmijail@...il.com>
---
 lib/hexdump.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/lib/hexdump.c b/lib/hexdump.c
index 7ea0969..ba9f384 100644
--- a/lib/hexdump.c
+++ b/lib/hexdump.c
@@ -123,6 +123,11 @@ int hex_dump_to_buffer(const void *buf, size_t len, int rowsize, int groupsize,
 		groupsize = 1;
 	if ((len % groupsize) != 0)	/* no mixed size output */
 		groupsize = 1;
+	
+	/* fall back to 1-byte groups if buf is not naturally aligned */
+	if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) &&
+	    (((uintptr_t)buf % groupsize) != 0))
+		groupsize = 1;

 	ngroups = len / groupsize;
 	ascii_column = rowsize * 2 + rowsize / groupsize + 1;
-- 
2.1.4

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