Re: [RFC PATCH 7/9] apple-gmux: add sysfs interface

[Hans de Goede]

Hi,

On 2/10/23 05:48, Orlando Chamberlain wrote:
> Allow reading gmux ports from userspace. When the unsafe module
> parameter allow_user_writes is true, writing 1 byte
> values is also allowed.
> 
> For example:
> 
> cd /sys/bus/acpi/devices/APP000B:00/physical_node/
> echo 4 > gmux_selected_port
> cat gmux_selected_port_data | xxd -p
> 
> Will show the gmux version information (00000005 in this case)

Please use debugfs for this and as part of the conversion
drop the #ifdef-s (debugfs has stubs for when not enabled)
and drop all the error checking of creating the files, debugfs
is deliberately designed to not have any error checking in
the setup / teardown code.

This also removes the need for the allow_user_writes parameter
replacing it with the new kernel lockdown mechanism. debugfs
will automatically block access to writable files when
the kernel is in lockdown mode.

Regards,

Hans




> Signed-off-by: Orlando Chamberlain <orlandoch.dev@xxxxxxxxx>
> ---
>  drivers/platform/x86/apple-gmux.c | 129 ++++++++++++++++++++++++++++++
>  1 file changed, 129 insertions(+)
> 
> diff --git a/drivers/platform/x86/apple-gmux.c b/drivers/platform/x86/apple-gmux.c
> index c38d6ef0c15a..756059d48393 100644
> --- a/drivers/platform/x86/apple-gmux.c
> +++ b/drivers/platform/x86/apple-gmux.c
> @@ -66,6 +66,11 @@ struct apple_gmux_data {
>  	enum vga_switcheroo_client_id switch_state_external;
>  	enum vga_switcheroo_state power_state;
>  	struct completion powerchange_done;
> +
> +#ifdef CONFIG_SYSFS
> +	/* sysfs data */
> +	int selected_port;
> +#endif /* CONFIG_SYSFS */
>  };
>  
>  static struct apple_gmux_data *apple_gmux_data;
> @@ -651,6 +656,121 @@ static void gmux_notify_handler(acpi_handle device, u32 value, void *context)
>  		complete(&gmux_data->powerchange_done);
>  }
>  
> +/**
> + * DOC: Sysfs Interface
> + *
> + * gmux ports can be read from userspace as a sysfs interface. For example:
> + *
> + * # echo 4 > /sys/bus/acpi/devices/APP000B:00/physical_node/gmux_selected_port
> + * # cat /sys/bus/acpi/devices/APP000B:00/physical_node/gmux_selected_port_data | xxd -p
> + * 00000005
> + *
> + * Reads 4 bytes from port 4 (GMUX_PORT_VERSION_MAJOR).
> + *
> + * Single byte writes are also supported, however this must be enabled with the
> + * unsafe allow_user_writes module parameter.
> + *
> + */
> +
> +#ifdef CONFIG_SYSFS
> +
> +static bool allow_user_writes;
> +module_param_unsafe(allow_user_writes, bool, 0);
> +MODULE_PARM_DESC(allow_user_writes, "Allow userspace to write to gmux ports (default: false) (bool)");
> +
> +static ssize_t gmux_selected_port_store(struct device *dev,
> +		struct device_attribute *attr, const char *sysfsbuf, size_t count)
> +{
> +	struct apple_gmux_data *gmux_data = dev_get_drvdata(dev);
> +	u8 port;
> +
> +	if (kstrtou8(sysfsbuf, 10, &port) < 0)
> +		return -EINVAL;
> +
> +	/* On pio gmux's, make sure the user doesn't access too high of a port. */
> +	if ((gmux_data->config == &apple_gmux_pio) &&
> +		port > (gmux_data->iolen - 4))
> +		return -EINVAL;
> +
> +	gmux_data->selected_port = port;
> +	return count;
> +}
> +
> +static ssize_t gmux_selected_port_show(struct device *dev,
> +		struct device_attribute *attr, char *sysfsbuf)
> +{
> +	struct apple_gmux_data *gmux_data = dev_get_drvdata(dev);
> +
> +	return sysfs_emit(sysfsbuf, "%d\n", gmux_data->selected_port);
> +}
> +
> +DEVICE_ATTR_RW(gmux_selected_port);
> +
> +static ssize_t gmux_selected_port_data_store(struct device *dev,
> +		struct device_attribute *attr, const char *sysfsbuf, size_t count)
> +{
> +	struct apple_gmux_data *gmux_data = dev_get_drvdata(dev);
> +
> +	if (count == 1)
> +		gmux_write8(gmux_data, gmux_data->selected_port, *sysfsbuf);
> +	else
> +		return -EINVAL;
> +
> +	return count;
> +}
> +
> +static ssize_t gmux_selected_port_data_show(struct device *dev,
> +		struct device_attribute *attr, char *sysfsbuf)
> +{
> +	struct apple_gmux_data *gmux_data = dev_get_drvdata(dev);
> +	u32 data;
> +
> +	data = gmux_read32(gmux_data, gmux_data->selected_port);
> +	memcpy(sysfsbuf, &data, sizeof(data));
> +
> +	return sizeof(data);
> +}
> +
> +struct device_attribute dev_attr_gmux_selected_port_data_rw = __ATTR_RW(gmux_selected_port_data);
> +struct device_attribute dev_attr_gmux_selected_port_data_ro = __ATTR_RO(gmux_selected_port_data);
> +
> +static int gmux_init_sysfs(struct pnp_dev *pnp)
> +{
> +	int ret;
> +
> +	ret = device_create_file(&pnp->dev, &dev_attr_gmux_selected_port);
> +	if (ret)
> +		return ret;
> +	if (allow_user_writes)
> +		ret = device_create_file(&pnp->dev, &dev_attr_gmux_selected_port_data_rw);
> +	else
> +		ret = device_create_file(&pnp->dev, &dev_attr_gmux_selected_port_data_ro);
> +	if (ret)
> +		device_remove_file(&pnp->dev, &dev_attr_gmux_selected_port);
> +	return ret;
> +}
> +
> +static void gmux_fini_sysfs(struct pnp_dev *pnp)
> +{
> +	device_remove_file(&pnp->dev, &dev_attr_gmux_selected_port);
> +	if (allow_user_writes)
> +		device_remove_file(&pnp->dev, &dev_attr_gmux_selected_port_data_rw);
> +	else
> +		device_remove_file(&pnp->dev, &dev_attr_gmux_selected_port_data_ro);
> +}
> +
> +#else
> +
> +static int gmux_init_sysfs(struct pnp_dev *pnp)
> +{
> +	return 0;
> +}
> +static void gmux_fini_sysfs(struct pnp_dev *pnp)
> +{
> +}
> +
> +#endif /* CONFIG_SYSFS */
> +
>  static int gmux_suspend(struct device *dev)
>  {
>  	struct pnp_dev *pnp = to_pnp_dev(dev);
> @@ -846,8 +966,16 @@ static int gmux_probe(struct pnp_dev *pnp, const struct pnp_device_id *id)
>  		goto err_register_handler;
>  	}
>  
> +	ret = gmux_init_sysfs(pnp);
> +	if (ret) {
> +		pr_err("Failed to register gmux sysfs entries\n");
> +		goto err_sysfs;
> +	}
> +
>  	return 0;
>  
> +err_sysfs:
> +	vga_switcheroo_unregister_handler();
>  err_register_handler:
>  	gmux_disable_interrupts(gmux_data);
>  	apple_gmux_data = NULL;
> @@ -877,6 +1005,7 @@ static void gmux_remove(struct pnp_dev *pnp)
>  {
>  	struct apple_gmux_data *gmux_data = pnp_get_drvdata(pnp);
>  
> +	gmux_fini_sysfs(pnp);
>  	vga_switcheroo_unregister_handler();
>  	gmux_disable_interrupts(gmux_data);
>  	if (gmux_data->gpe >= 0) {