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Message-ID: <ZMuR0W303WCbS1K0@smile.fi.intel.com>
Date: Thu, 3 Aug 2023 14:38:57 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Bartosz Golaszewski <brgl@...ev.pl>
Cc: Linus Walleij <linus.walleij@...aro.org>,
Kent Gibson <warthog618@...il.com>,
Viresh Kumar <viresh.kumar@...aro.org>,
Geert Uytterhoeven <geert@...ux-m68k.org>,
linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [RFC PATCH] gpio: consumer: new virtual driver
On Wed, Aug 02, 2023 at 05:28:08PM +0200, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
>
> The GPIO subsystem has a serious problem with undefined behavior and
> use-after-free bugs on hot-unplug of GPIO chips. This can be considered a
> corner-case by some as most GPIO controllers are enabled early in the
> boot process and live until the system goes down but most GPIO drivers
> do allow unbind over sysfs, many are loadable modules that can be (force)
> unloaded and there are also GPIO devices that can be dynamically detached,
> for instance CP2112 which is a USB GPIO expender.
>
> Bugs can be triggered both from user-space as well as by in-kernel users.
> We have the means of testing it from user-space via the character device
> but the issues manifest themselves differently in the kernel.
>
> This is a proposition of adding a new virtual driver - a configurable
> GPIO consumer that can be configured over configfs (similarly to
> gpio-sim).
>
> The configfs interface allows users to create dynamic GPIO lookup tables
> that are registered with the GPIO subsystem. Every config group
> represents a consumer device. Every sub-group represents a single GPIO
> lookup. The device can work in three modes: just keeping the line
> active, toggling it every second or requesting its interrupt and
> reporting edges. Every lookup allows to specify the key, offset and
> flags as per the lookup struct defined in linux/gpio/machine.h.
>
> The module together with gpio-sim allows to easily trigger kernel
> hot-unplug errors. A simple use-case is to create a simulated chip,
> setup the consumer to lookup one of its lines in 'monitor' mode, unbind
> the simulator, unbind the consumer and observe the fireworks in dmesg.
>
> This driver is aimed as a helper in tackling the hot-unplug problem in
> GPIO as well as basis for future regression testing once the fixes are
> upstream.
...
> @@ -1796,6 +1796,13 @@ config GPIO_SIM
> This enables the GPIO simulator - a configfs-based GPIO testing
> driver.
>
> +config GPIO_CONSUMER
> + tristate "GPIO Consumer Testing Module"
> + select CONFIGFS_FS
> + help
> + This enables the configurable, configfs-based virtual GPIO consumer
> + testing driver.
I believe the agreement (as mentioned in this file) is to keep sorted by config
names, so CONSUMER is definitely should be earlier than SIM.
...
> +#include <linux/completion.h>
> +#include <linux/configfs.h>
> +#include <linux/device.h>
> +#include <linux/gpio/consumer.h>
> +#include <linux/gpio/machine.h>
> +#include <linux/idr.h>
> +#include <linux/interrupt.h>
> +#include <linux/jiffies.h>
> +#include <linux/kernel.h>
> +#include <linux/limits.h>
> +#include <linux/list.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/notifier.h>
> +#include <linux/of_platform.h>
Wrong header. Use mod_devicetable.h.
> +#include <linux/platform_device.h>
> +#include <linux/printk.h>
> +#include <linux/property.h>
> +#include <linux/slab.h>
> +#include <linux/string.h>
> +#include <linux/timer.h>
And general recommendation is to revisit this block and refine it accordingly.
...
> +enum gpio_consumer_function {
> + GPIO_CONSUMER_FUNCTION_ACTIVE = 0,
= 0 is guaranteed by C standard, why do you need it be explicit?
> + GPIO_CONSUMER_FUNCTION_TOGGLE,
> + GPIO_CONSUMER_FUNCTION_MONITOR,
> + __GPIO_CONSUMER_FUNCTION_LAST,
No comma in terminator line.
> +};
...
> +static void gpio_consumer_on_timer(struct timer_list *timer)
> +{
> + struct gpio_consumer_timer_data *timer_data = to_timer_data(timer);
> + timer_data->val = timer_data->val == 0 ? 1 : 0;
timer_data->val = timer_data->val ? 0 : 1;
is shorter, but what is showing better the intention is
timer_data->val ^= 1;
> + gpiod_set_value_cansleep(timer_data->desc, timer_data->val);
> + mod_timer(&timer_data->timer, jiffies + msecs_to_jiffies(1000));
> +}
...
> + ret = match_string(gpio_consumer_function_strings, -1, function_prop);
> + if (ret < 0)
> + return dev_err_probe(dev, -EINVAL,
Why not
return dev_err_probe(dev, ret,
?
> + "Invalid consumer function: '%s'\n",
> + function_prop);
...
> + flags = function == GPIO_CONSUMER_FUNCTION_MONITOR ?
> + GPIOD_IN : GPIOD_OUT_HIGH;
> + for (i = 0; i < num_lines; i++) {
> + desc = devm_gpiod_get(dev, lines[i], flags);
> + if (IS_ERR(desc))
> + return dev_err_probe(dev, PTR_ERR(desc),
> + "Failed to get GPIO '%s'\n",
> + lines[i]);
Would it make sense to request GPIOs via devm_gpiod_get_array() and then try
the rest on them in a loop?
> + }
...
> +static int gpio_consumer_bus_notifier_call(struct notifier_block *nb,
> + unsigned long action, void *data)
> +{
> + struct gpio_consumer_device *consumer;
> + struct device *dev = data;
> + char devname[32];
> +
> + consumer = container_of(nb, struct gpio_consumer_device, bus_notifier);
> + snprintf(devname, sizeof(devname), "gpio-virtual-consumer.%d",
> + consumer->id);
> + if (strcmp(dev_name(dev), devname) == 0) {
if (strcmp(dev_name(dev), devname))
return NOTIFY_DONE;
?
> + switch (action) {
> + case BUS_NOTIFY_BOUND_DRIVER:
> + consumer->driver_bound = true;
> + break;
> + case BUS_NOTIFY_DRIVER_NOT_BOUND:
> + consumer->driver_bound = false;
> + break;
> + default:
> + return NOTIFY_DONE;
> + }
> +
> + complete(&consumer->probe_completion);
> + return NOTIFY_OK;
> + }
> +
> + return NOTIFY_DONE;
> +}
...
> +static ssize_t
> +gpio_consumer_lookup_config_offset_store(struct config_item *item,
> + const char *page, size_t count)
> +{
> + struct gpio_consumer_lookup *lookup = to_gpio_consumer_lookup(item);
> + struct gpio_consumer_device *dev = lookup->parent;
> + int offset, ret;
> +
> + ret = kstrtoint(page, 0, &offset);
> + if (ret)
> + return ret;
> +
> + /* Use -1 to indicate lookup by name. */
> + if (offset > (U16_MAX - 1))
> + return -EINVAL;
So, offset here may be negative. Is it okay?
> + mutex_lock(&dev->lock);
> +
> + if (gpio_consumer_device_is_live_unlocked(dev)) {
> + mutex_unlock(&dev->lock);
> + return -EBUSY;
> + }
> +
> + lookup->offset = offset;
> +
> + mutex_unlock(&dev->lock);
> +
> + return count;
> +}
...
> + if (flags & GPIO_OPEN_DRAIN)
> + repr = "open-drain";
> + else if (flags & GPIO_OPEN_SOURCE)
> + repr = "open-source";
Can it be both flags set?
> + else
> + repr = "push-pull";
...
> + if (sysfs_streq(page, "push-pull")) {
> + lookup->flags &= ~(GPIO_OPEN_DRAIN | GPIO_OPEN_SOURCE);
> + } else if (sysfs_streq(page, "open-drain")) {
> + lookup->flags &= ~GPIO_OPEN_SOURCE;
> + lookup->flags |= GPIO_OPEN_DRAIN;
> + } else if (sysfs_streq(page, "open-source")) {
> + lookup->flags &= ~GPIO_OPEN_DRAIN;
> + lookup->flags |= GPIO_OPEN_SOURCE;
> + } else {
> + count = -EINVAL;
> + }
I prefer to see some kind of the array of constant string literals and do
sysfs_match_string() here
lookup->flags &= ~(GPIO_OPEN_DRAIN | GPIO_OPEN_SOURCE);
flag = sysfs_match_string(...);
if (flag < 0)
count = flag
else
lookup->flags |= flag;
(or something similar). And respectively indexed access above.
...
> + flags = gpio_consumer_lookup_get_flags(item);
> +
> + if (flags & GPIO_PULL_UP)
> + repr = "pull-up";
> + else if (flags & GPIO_PULL_DOWN)
> + repr = "pull-down";
> + else if (flags & GPIO_PULL_DISABLE)
> + repr = "pull-disabled";
> + else
> + repr = "as-is";
...
> + if (sysfs_streq(page, "pull-up")) {
> + lookup->flags &= ~(GPIO_PULL_DOWN | GPIO_PULL_DISABLE);
> + lookup->flags |= GPIO_PULL_UP;
> + } else if (sysfs_streq(page, "pull-down")) {
> + lookup->flags &= ~(GPIO_PULL_UP | GPIO_PULL_DISABLE);
> + lookup->flags |= GPIO_PULL_DOWN;
> + } else if (sysfs_streq(page, "pull-disabled")) {
> + lookup->flags &= ~(GPIO_PULL_UP | GPIO_PULL_DOWN);
> + lookup->flags |= GPIO_PULL_DISABLE;
> + } else if (sysfs_streq(page, "as-is")) {
> + lookup->flags &= ~(GPIO_PULL_UP | GPIO_PULL_DOWN |
> + GPIO_PULL_DISABLE);
> + } else {
> + count = -EINVAL;
> + }
The above is more tricky, but still consider similar approach.
...
> + num_entries = list_count_nodes(&dev->lookup_list);
> + table = kzalloc(sizeof(*table) + num_entries * sizeof(*table->table),
struct_size() ?
> + GFP_KERNEL);
> + if (!table)
> + return -ENOMEM;
...
> + if (list_empty(&dev->lookup_list))
> + return -ENODATA;
Instead you may count nodes here and if 0, return an error, otherwise pass it
to the callee.
> + swnode = gpio_consumer_make_device_swnode(dev);
> + if (IS_ERR(swnode))
> + return PTR_ERR(swnode);
...
> +static ssize_t
> +gpio_consumer_device_config_live_store(struct config_item *item,
> + const char *page, size_t count)
> +{
> + struct gpio_consumer_device *dev = to_gpio_consumer_device(item);
> + bool live;
> + int ret;
> +
> + ret = kstrtobool(page, &live);
> + if (ret)
> + return ret;
> +
> + mutex_lock(&dev->lock);
> +
> + if ((!live && !gpio_consumer_device_is_live_unlocked(dev)) ||
> + (live && gpio_consumer_device_is_live_unlocked(dev)))
if (live ^ gpio_consumer_device_is_live_unlocked(dev))
?
> + ret = -EPERM;
> + else if (live)
> + ret = gpio_consumer_device_activate_unlocked(dev);
> + else
> + gpio_consumer_device_deactivate_unlocked(dev);
> +
> + mutex_unlock(&dev->lock);
> +
> + return ret ?: count;
> +}
...
> +static int __init gpio_consumer_init(void)
> +{
> + int ret;
> +
> + ret = platform_driver_register(&gpio_consumer_driver);
> + if (ret) {
> + pr_err("Failed to register the gpio-consumer platform driver: %d\n",
Isn't name will be duplicated via pr_fmt()?
> + ret);
If yes, can be shortened to
pr_err("Failed to register the driver: %d\n", ret);
> + return ret;
> + }
> +
> + config_group_init(&gpio_consumer_config_subsys.su_group);
> + mutex_init(&gpio_consumer_config_subsys.su_mutex);
> + ret = configfs_register_subsystem(&gpio_consumer_config_subsys);
> + if (ret) {
> + pr_err("Failed to register the '%s' configfs subsystem: %d\n",
> + gpio_consumer_config_subsys.su_group.cg_item.ci_namebuf,
> + ret);
> + mutex_destroy(&gpio_consumer_config_subsys.su_mutex);
> + platform_driver_unregister(&gpio_consumer_driver);
> + return ret;
> + }
> +
> + return 0;
> +}
--
With Best Regards,
Andy Shevchenko
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