linux-kernel - [PATCH] bitops: Fix shift overflow in GENMASK macros

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Date:	Mon,  3 Nov 2014 18:39:58 +0100
From:	Maxime COQUELIN <maxime.coquelin@...com>
To:	gong.chen@...ux.intel.com, Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	" Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, tytso@....edu,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	kernel@...inux.com, maxime.coquelin@...com, eric.paire@...com
Subject: [PATCH] bitops: Fix shift overflow in GENMASK macros

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.

Fixes: 10ef6b0dffe404bcc54e94cb2ca1a5b18445a66b
Cc: <stable@...r.kernel.org> #v3.13+
Reported-by: Eric Paire <eric.paire@...com>
Signed-off-by: Maxime Coquelin <maxime.coquelin@...com>
---
 include/linux/bitops.h | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index be5fd38..81f9725 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -18,8 +18,12 @@
  * 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 >> ((BITS_PER_LONG - 1) - (h))) & ~((1UL << (l)) - 1))
+
+#define GENMASK_ULL(h, l) \
+	((~0ULL >> ((BITS_PER_LONG_LONG - 1) - (h))) & ~((1ULL << (l)) - 1))
+
 
 extern unsigned int __sw_hweight8(unsigned int w);
 extern unsigned int __sw_hweight16(unsigned int w);
-- 
1.9.1

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