linux-kernel - [PATCH 3.16.y-ckt 027/168] bitops: Fix shift overflow in GENMASK macros

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Message-Id: <1418653622-21105-28-git-send-email-luis.henriques@canonical.com>
Date:	Mon, 15 Dec 2014 14:24:41 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Maxime Coquelin <maxime.coquelin@...com>,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	linux@...musvillemoes.dk, gong.chen@...ux.intel.com,
	John Sullivan <jsrhbz@...argh.force9.co.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Theodore Ts'o <tytso@....edu>, Ingo Molnar <mingo@...nel.org>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 027/168] bitops: Fix shift overflow in GENMASK macros

3.16.7-ckt3 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Maxime COQUELIN <maxime.coquelin@...com>

commit 00b4d9a14125f1e51874def2b9de6092e007412d upstream.

On some 32 bits architectures, including x86, GENMASK(31, 0) returns 0
instead of the expected ~0UL.

This is the same on some 64 bits architectures with GENMASK_ULL(63, 0).

This is due to an overflow in the shift operand, 1 << 32 for GENMASK,
1 << 64 for GENMASK_ULL.

Reported-by: Eric Paire <eric.paire@...com>
Suggested-by: Rasmus Villemoes <linux@...musvillemoes.dk>
Signed-off-by: Maxime Coquelin <maxime.coquelin@...com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: linux@...musvillemoes.dk
Cc: gong.chen@...ux.intel.com
Cc: John Sullivan <jsrhbz@...argh.force9.co.uk>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Theodore Ts'o <tytso@....edu>
Fixes: 10ef6b0dffe4 ("bitops: Introduce a more generic BITMASK macro")
Link: http://lkml.kernel.org/r/1415267659-10563-1-git-send-email-maxime.coquelin@st.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 include/linux/bitops.h | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index cbc5833fb221..38b5f5c88c18 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -18,8 +18,11 @@
  * position @h. For example
  * GENMASK_ULL(39, 21) gives us the 64bit vector 0x000000ffffe00000.
  */
-#define GENMASK(h, l)		(((U32_C(1) << ((h) - (l) + 1)) - 1) << (l))
-#define GENMASK_ULL(h, l)	(((U64_C(1) << ((h) - (l) + 1)) - 1) << (l))
+#define GENMASK(h, l) \
+	(((~0UL) << (l)) & (~0UL >> (BITS_PER_LONG - 1 - (h))))
+
+#define GENMASK_ULL(h, l) \
+	(((~0ULL) << (l)) & (~0ULL >> (BITS_PER_LONG_LONG - 1 - (h))))
 
 extern unsigned int __sw_hweight8(unsigned int w);
 extern unsigned int __sw_hweight16(unsigned int w);
-- 
2.1.3

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