[PATCH 3.19.y-ckt 118/251] regmap: Fix possible shift overflow in regmap_field_init()

[Kamal Mostafa]

3.19.8-ckt4 -stable review patch.  If anyone has any objections, please let me know.

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

From: Maxime Coquelin <maxime.coquelin at st.com>

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.

Signed-off-by: Maxime Coquelin <maxime.coquelin at st.com>
Signed-off-by: Mark Brown <broonie at kernel.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/base/regmap/regmap.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/base/regmap/regmap.c b/drivers/base/regmap/regmap.c
index a434df6..b389c1d 100644
--- a/drivers/base/regmap/regmap.c
+++ b/drivers/base/regmap/regmap.c
@@ -944,11 +944,10 @@ EXPORT_SYMBOL_GPL(devm_regmap_init);
 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 = GENMASK(reg_field.msb, reg_field.lsb);
 	rm_field->id_size = reg_field.id_size;
 	rm_field->id_offset = reg_field.id_offset;
 }
-- 
1.9.1