Linux 4.9.176

[thirdparty/kernel/stable-queue.git] / releases / 4.9.176 / 0012-bitops-avoid-integer-overflow-in-GENMASK-_ULL.patch

From a2783e3dab88b3062ed1612187b90c7fc36d67a9 Mon Sep 17 00:00:00 2001
From: Matthias Kaehlcke <mka@chromium.org>
Date: Fri, 8 Sep 2017 16:14:33 -0700
Subject: [PATCH 12/76] bitops: avoid integer overflow in GENMASK(_ULL)

commit c32ee3d9abd284b4fcaacc250b101f93829c7bae upstream.

GENMASK(_ULL) performs a left-shift of ~0UL(L), which technically
results in an integer overflow.  clang raises a warning if the overflow
occurs in a preprocessor expression.  Clear the low-order bits through a
substraction instead of the left-shift to avoid the overflow.

(akpm: no change in .text size in my testing)

Link: http://lkml.kernel.org/r/20170803212020.24939-1-mka@chromium.org
Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 include/linux/bitops.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index a83c822c35c2..8fbe259b197c 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -19,10 +19,11 @@
  * GENMASK_ULL(39, 21) gives us the 64bit vector 0x000000ffffe00000.
  */
 #define GENMASK(h, l) \
-	(((~0UL) << (l)) & (~0UL >> (BITS_PER_LONG - 1 - (h))))
+	(((~0UL) - (1UL << (l)) + 1) & (~0UL >> (BITS_PER_LONG - 1 - (h))))
 
 #define GENMASK_ULL(h, l) \
-	(((~0ULL) << (l)) & (~0ULL >> (BITS_PER_LONG_LONG - 1 - (h))))
+	(((~0ULL) - (1ULL << (l)) + 1) & \
+	 (~0ULL >> (BITS_PER_LONG_LONG - 1 - (h))))
 
 extern unsigned int __sw_hweight8(unsigned int w);
 extern unsigned int __sw_hweight16(unsigned int w);
-- 
2.21.0