linux-kernel - [PATCH 3.12 108/124] regmap: Fix possible shift overflow in regmap_field

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Message-Id: <0e5220a40f655782e493f3aad6d869090258a6a3.1438076484.git.jslaby@suse.cz>
Date:	Tue, 28 Jul 2015 11:52:49 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	Maxime Coquelin <maxime.coquelin@...com>,
	Mark Brown <broonie@...nel.org>, Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 108/124] regmap: Fix possible shift overflow in regmap_field_init()

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

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

===============

commit 921cc29473a0d7c109105c1876ddb432f4a4be7d upstream.

The way the mask is generated in regmap_field_init() is wrong.
Indeed, a field initialized with msb = 31 and lsb = 0 provokes a shift
overflow while calculating the mask field.

On some 32 bits architectures, such as x86, the generated mask is 0,
instead of the expected 0xffffffff.

This patch uses GENMASK() to fix the problem, as this macro is already safe
regarding shift overflow.

[-js: in 3.12, we do not have GENMASK for general access. Define
locally as RM_GENMASK.]

Signed-off-by: Maxime Coquelin <maxime.coquelin@...com>
Signed-off-by: Mark Brown <broonie@...nel.org>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 drivers/base/regmap/regmap.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/base/regmap/regmap.c b/drivers/base/regmap/regmap.c
index 45aec73d09bd..8ece0fe4033f 100644
--- a/drivers/base/regmap/regmap.c
+++ b/drivers/base/regmap/regmap.c
@@ -813,14 +813,16 @@ struct regmap *devm_regmap_init(struct device *dev,
 }
 EXPORT_SYMBOL_GPL(devm_regmap_init);
 
+#define RM_GENMASK(h, l) \
+	        (((~0UL) << (l)) & (~0UL >> (BITS_PER_LONG - 1 - (h))))
+
 static void regmap_field_init(struct regmap_field *rm_field,
 	struct regmap *regmap, struct reg_field reg_field)
 {
-	int field_bits = reg_field.msb - reg_field.lsb + 1;
 	rm_field->regmap = regmap;
 	rm_field->reg = reg_field.reg;
 	rm_field->shift = reg_field.lsb;
-	rm_field->mask = ((BIT(field_bits) - 1) << reg_field.lsb);
+	rm_field->mask = RM_GENMASK(reg_field.msb, reg_field.lsb);
 }
 
 /**
-- 
2.4.6

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