linux-kernel - [PATCH v1] pwm: microchip-core: fix incorrect comparison with max period

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250122-pastor-fancied-0b993da2d2d2@spud>
Date: Wed, 22 Jan 2025 14:42:56 +0000
From: Conor Dooley <conor@...nel.org>
To: linux-pwm@...r.kernel.org
Cc: conor@...nel.org,
	Conor Dooley <conor.dooley@...rochip.com>,
	stable@...r.kernel.org,
	Daire McNamara <daire.mcnamara@...rochip.com>,
	Uwe Kleine-König <ukleinek@...nel.org>,
	Thierry Reding <thierry.reding@...il.com>,
	linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v1] pwm: microchip-core: fix incorrect comparison with max period

From: Conor Dooley <conor.dooley@...rochip.com>

In mchp_core_pwm_apply_locked(), if hw_period_steps is equal to its max,
an error is reported and .apply fails. The max value is actually a
permitted value however, and so this check can fail where multiple
channels are enabled.

For example, the first channel to be configured requests a period that
sets hw_period_steps to the maximum value, and when a second channel
is enabled the driver reads hw_period_steps back from the hardware and
finds it to be the maximum possible value, triggering the warning on a
permitted value. The value to be avoided is 255 (PERIOD_STEPS_MAX + 1),
as that will produce undesired behaviour, so test for greater than,
rather than equal to.

Fixes: 2bf7ecf7b4ff ("pwm: add microchip soft ip corePWM driver")
CC: stable@...r.kernel.org
Signed-off-by: Conor Dooley <conor.dooley@...rochip.com>
---
CC: Conor Dooley <conor.dooley@...rochip.com>
CC: Daire McNamara <daire.mcnamara@...rochip.com>
CC: Uwe Kleine-König <ukleinek@...nel.org>
CC: Thierry Reding <thierry.reding@...il.com>
CC: linux-riscv@...ts.infradead.org
CC: linux-pwm@...r.kernel.org
CC: linux-kernel@...r.kernel.org
---
 drivers/pwm/pwm-microchip-core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pwm/pwm-microchip-core.c b/drivers/pwm/pwm-microchip-core.c
index c1f2287b8e97..12821b4bbf97 100644
--- a/drivers/pwm/pwm-microchip-core.c
+++ b/drivers/pwm/pwm-microchip-core.c
@@ -327,7 +327,7 @@ static int mchp_core_pwm_apply_locked(struct pwm_chip *chip, struct pwm_device *
 		 * mchp_core_pwm_calc_period().
 		 * The period is locked and we cannot change this, so we abort.
 		 */
-		if (hw_period_steps == MCHPCOREPWM_PERIOD_STEPS_MAX)
+		if (hw_period_steps > MCHPCOREPWM_PERIOD_STEPS_MAX)
 			return -EINVAL;
 
 		prescale = hw_prescale;
-- 
2.45.2