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-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <20231215023805.63289-4-warthog618@gmail.com>
Date: Fri, 15 Dec 2023 10:38:03 +0800
From: Kent Gibson <warthog618@...il.com>
To: linux-kernel@...r.kernel.org,
	linux-gpio@...r.kernel.org,
	brgl@...ev.pl,
	linus.walleij@...aro.org,
	andy@...nel.org
Cc: Kent Gibson <warthog618@...il.com>
Subject: [PATCH v3 3/5] gpiolib: cdev: reduce locking in gpio_desc_to_lineinfo()

Reduce the time holding the gpio_lock by snapshotting the desc flags,
rather than testing them individually while holding the lock.

Accept that the calculation of the used field is inherently racy, and
only check the availability of the line from pinctrl if other checks
pass, so avoiding the check for lines that are otherwise in use.

Signed-off-by: Kent Gibson <warthog618@...il.com>
---
 drivers/gpio/gpiolib-cdev.c | 74 ++++++++++++++++++-------------------
 1 file changed, 36 insertions(+), 38 deletions(-)

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index 5ba900e5461a..c140bcd63361 100644
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -2388,74 +2388,72 @@ static void gpio_desc_to_lineinfo(struct gpio_desc *desc,
 				  struct gpio_v2_line_info *info)
 {
 	struct gpio_chip *gc = desc->gdev->chip;
-	bool ok_for_pinctrl;
-	unsigned long flags;
+	unsigned long dflags;
 
 	memset(info, 0, sizeof(*info));
 	info->offset = gpio_chip_hwgpio(desc);
 
-	/*
-	 * This function takes a mutex so we must check this before taking
-	 * the spinlock.
-	 *
-	 * FIXME: find a non-racy way to retrieve this information. Maybe a
-	 * lock common to both frameworks?
-	 */
-	ok_for_pinctrl = pinctrl_gpio_can_use_line(gc, info->offset);
+	scoped_guard(spinlock_irqsave, &gpio_lock) {
+		if (desc->name)
+			strscpy(info->name, desc->name, sizeof(info->name));
 
-	spin_lock_irqsave(&gpio_lock, flags);
+		if (desc->label)
+			strscpy(info->consumer, desc->label,
+				sizeof(info->consumer));
 
-	if (desc->name)
-		strscpy(info->name, desc->name, sizeof(info->name));
-
-	if (desc->label)
-		strscpy(info->consumer, desc->label, sizeof(info->consumer));
+		dflags = READ_ONCE(desc->flags);
+	}
 
 	/*
-	 * Userspace only need to know that the kernel is using this GPIO so
-	 * it can't use it.
+	 * Userspace only need know that the kernel is using this GPIO so it
+	 * can't use it.
+	 * The calculation of the used flag is slightly racy, as it may read
+	 * desc, gc and pinctrl state without a lock covering all three at
+	 * once.  Worst case if the line is in transition and the calculation
+	 * is inconsistent then it looks to the user like they performed the
+	 * read on the other side of the transition - but that can always
+	 * happen.
+	 * The definitive test that a line is available to userspace is to
+	 * request it.
 	 */
-	info->flags = 0;
-	if (test_bit(FLAG_REQUESTED, &desc->flags) ||
-	    test_bit(FLAG_IS_HOGGED, &desc->flags) ||
-	    test_bit(FLAG_USED_AS_IRQ, &desc->flags) ||
-	    test_bit(FLAG_EXPORT, &desc->flags) ||
-	    test_bit(FLAG_SYSFS, &desc->flags) ||
+	if (test_bit(FLAG_REQUESTED, &dflags) ||
+	    test_bit(FLAG_IS_HOGGED, &dflags) ||
+	    test_bit(FLAG_USED_AS_IRQ, &dflags) ||
+	    test_bit(FLAG_EXPORT, &dflags) ||
+	    test_bit(FLAG_SYSFS, &dflags) ||
 	    !gpiochip_line_is_valid(gc, info->offset) ||
-	    !ok_for_pinctrl)
+	    !pinctrl_gpio_can_use_line(gc, info->offset))
 		info->flags |= GPIO_V2_LINE_FLAG_USED;
 
-	if (test_bit(FLAG_IS_OUT, &desc->flags))
+	if (test_bit(FLAG_IS_OUT, &dflags))
 		info->flags |= GPIO_V2_LINE_FLAG_OUTPUT;
 	else
 		info->flags |= GPIO_V2_LINE_FLAG_INPUT;
 
-	if (test_bit(FLAG_ACTIVE_LOW, &desc->flags))
+	if (test_bit(FLAG_ACTIVE_LOW, &dflags))
 		info->flags |= GPIO_V2_LINE_FLAG_ACTIVE_LOW;
 
-	if (test_bit(FLAG_OPEN_DRAIN, &desc->flags))
+	if (test_bit(FLAG_OPEN_DRAIN, &dflags))
 		info->flags |= GPIO_V2_LINE_FLAG_OPEN_DRAIN;
-	if (test_bit(FLAG_OPEN_SOURCE, &desc->flags))
+	if (test_bit(FLAG_OPEN_SOURCE, &dflags))
 		info->flags |= GPIO_V2_LINE_FLAG_OPEN_SOURCE;
 
-	if (test_bit(FLAG_BIAS_DISABLE, &desc->flags))
+	if (test_bit(FLAG_BIAS_DISABLE, &dflags))
 		info->flags |= GPIO_V2_LINE_FLAG_BIAS_DISABLED;
-	if (test_bit(FLAG_PULL_DOWN, &desc->flags))
+	if (test_bit(FLAG_PULL_DOWN, &dflags))
 		info->flags |= GPIO_V2_LINE_FLAG_BIAS_PULL_DOWN;
-	if (test_bit(FLAG_PULL_UP, &desc->flags))
+	if (test_bit(FLAG_PULL_UP, &dflags))
 		info->flags |= GPIO_V2_LINE_FLAG_BIAS_PULL_UP;
 
-	if (test_bit(FLAG_EDGE_RISING, &desc->flags))
+	if (test_bit(FLAG_EDGE_RISING, &dflags))
 		info->flags |= GPIO_V2_LINE_FLAG_EDGE_RISING;
-	if (test_bit(FLAG_EDGE_FALLING, &desc->flags))
+	if (test_bit(FLAG_EDGE_FALLING, &dflags))
 		info->flags |= GPIO_V2_LINE_FLAG_EDGE_FALLING;
 
-	if (test_bit(FLAG_EVENT_CLOCK_REALTIME, &desc->flags))
+	if (test_bit(FLAG_EVENT_CLOCK_REALTIME, &dflags))
 		info->flags |= GPIO_V2_LINE_FLAG_EVENT_CLOCK_REALTIME;
-	else if (test_bit(FLAG_EVENT_CLOCK_HTE, &desc->flags))
+	else if (test_bit(FLAG_EVENT_CLOCK_HTE, &dflags))
 		info->flags |= GPIO_V2_LINE_FLAG_EVENT_CLOCK_HTE;
-
-	spin_unlock_irqrestore(&gpio_lock, flags);
 }
 
 struct gpio_chardev_data {
-- 
2.39.2


Powered by blists - more mailing lists

Powered by Openwall GNU/*/Linux Powered by OpenVZ