linux-kernel - [PATCH AUTOSEL 6.13 27/28] objtool, regulator: rk808: Remove potential undefined behavior in rk806_set_mode

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Message-Id: <20250407181224.3180941-27-sashal@kernel.org>
Date: Mon,  7 Apr 2025 14:12:17 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Josh Poimboeuf <jpoimboe@...nel.org>,
	kernel test robot <lkp@...el.com>,
	Ingo Molnar <mingo@...nel.org>,
	Mark Brown <broonie@...nel.org>,
	Liam Girdwood <lgirdwood@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Sasha Levin <sashal@...nel.org>
Subject: [PATCH AUTOSEL 6.13 27/28] objtool, regulator: rk808: Remove potential undefined behavior in rk806_set_mode_dcdc()

From: Josh Poimboeuf <jpoimboe@...nel.org>

[ Upstream commit 29c578c848402a34e8c8e115bf66cb6008b77062 ]

If 'ctr_bit' is negative, the shift counts become negative, causing a
shift of bounds and undefined behavior.

Presumably that's not possible in normal operation, but the code
generation isn't optimal.  And undefined behavior should be avoided
regardless.

Improve code generation and remove the undefined behavior by converting
the signed variables to unsigned.

Fixes the following warning with an UBSAN kernel:

  vmlinux.o: warning: objtool: rk806_set_mode_dcdc() falls through to next function rk806_get_mode_dcdc()
  vmlinux.o: warning: objtool: .text.rk806_set_mode_dcdc: unexpected end of section

Reported-by: kernel test robot <lkp@...el.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Acked-by: Mark Brown <broonie@...nel.org>
Cc: Liam Girdwood <lgirdwood@...il.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Link: https://lore.kernel.org/r/2023abcddf3f524ba478d64339996f25dc4097d2.1742852847.git.jpoimboe@kernel.org
Closes: https://lore.kernel.org/oe-kbuild-all/202503182350.52KeHGD4-lkp@intel.com/
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/regulator/rk808-regulator.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/regulator/rk808-regulator.c b/drivers/regulator/rk808-regulator.c
index 7d82bd1b36dfc..1e8142479656a 100644
--- a/drivers/regulator/rk808-regulator.c
+++ b/drivers/regulator/rk808-regulator.c
@@ -270,8 +270,8 @@ static const unsigned int rk817_buck1_4_ramp_table[] = {
 
 static int rk806_set_mode_dcdc(struct regulator_dev *rdev, unsigned int mode)
 {
-	int rid = rdev_get_id(rdev);
-	int ctr_bit, reg;
+	unsigned int rid = rdev_get_id(rdev);
+	unsigned int ctr_bit, reg;
 
 	reg = RK806_POWER_FPWM_EN0 + rid / 8;
 	ctr_bit = rid % 8;
-- 
2.39.5