Re: [PATCH v11 08/15] platform/x86: dell-smbios: Add a sysfs interface for SMBIOS tokens

["Pali Rohár" <pali.rohar@gmail.com>]

On Friday 20 October 2017 12:40:23 Mario Limonciello wrote:
> Currently userspace tools can access system tokens via the dcdbas
> kernel module and a SMI call that will cause the platform to execute
> SMM code.
> 
> With a goal in mind of deprecating the dcdbas kernel module a different
> method for accessing these tokens from userspace needs to be created.
> 
> This is intentionally marked to only be readable as a process with
> CAP_SYS_ADMIN as it can contain sensitive information about the
> platform's configuration.
> 
> While adding this interface I found that some tokens are duplicated.
> These need to be ignored from sysfs to avoid duplicate files.
> 
> MAINTAINERS was missing for this driver.  Add myself and Pali to
> maintainers list for it.
> 
> Signed-off-by: Mario Limonciello <mario.limonciello@dell.com>
> Reviewed-by: Edward O'Callaghan <quasisec@google.com>
> ---
>  .../ABI/testing/sysfs-platform-dell-smbios         |  21 ++
>  MAINTAINERS                                        |   7 +
>  drivers/platform/x86/dell-smbios.c                 | 212 ++++++++++++++++++++-
>  3 files changed, 239 insertions(+), 1 deletion(-)
>  create mode 100644 Documentation/ABI/testing/sysfs-platform-dell-smbios
> 
> diff --git a/Documentation/ABI/testing/sysfs-platform-dell-smbios b/Documentation/ABI/testing/sysfs-platform-dell-smbios
> new file mode 100644
> index 000000000000..205d3b6361e0
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-platform-dell-smbios
> @@ -0,0 +1,21 @@
> +What:		/sys/devices/platform/<platform>/tokens/*
> +Date:		November 2017
> +KernelVersion:	4.15
> +Contact:	"Mario Limonciello" <mario.limonciello@dell.com>
> +Description:
> +		A read-only description of Dell platform tokens
> +		available on the machine.
> +
> +		Each token attribute is available as a pair of
> +		sysfs attributes readable by a process with
> +		CAP_SYS_ADMIN.
> +
> +		For example the token ID "5" would be available
> +		as the following attributes:
> +
> +		0005_location
> +		0005_value
> +
> +		Tokens will vary from machine to machine, and
> +		only tokens available on that machine will be
> +		displayed.
> diff --git a/MAINTAINERS b/MAINTAINERS
> index f4cf35950b08..09e774f1d0b2 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -3978,6 +3978,13 @@ M:	"Maciej W. Rozycki" <macro@linux-mips.org>
>  S:	Maintained
>  F:	drivers/net/fddi/defxx.*
>  
> +DELL SMBIOS DRIVER
> +M:	Pali Rohár <pali.rohar@gmail.com>
> +M:	Mario Limonciello <mario.limonciello@dell.com>
> +L:	platform-driver-x86@vger.kernel.org
> +S:	Maintained
> +F:	drivers/platform/x86/dell-smbios.*
> +
>  DELL LAPTOP DRIVER
>  M:	Matthew Garrett <mjg59@srcf.ucam.org>
>  M:	Pali Rohár <pali.rohar@gmail.com>
> diff --git a/drivers/platform/x86/dell-smbios.c b/drivers/platform/x86/dell-smbios.c
> index 7e779278d054..9e2b396861bb 100644
> --- a/drivers/platform/x86/dell-smbios.c
> +++ b/drivers/platform/x86/dell-smbios.c
> @@ -16,10 +16,12 @@
>  
>  #include <linux/kernel.h>
>  #include <linux/module.h>
> +#include <linux/capability.h>
>  #include <linux/dmi.h>
>  #include <linux/err.h>
>  #include <linux/gfp.h>
>  #include <linux/mutex.h>
> +#include <linux/platform_device.h>
>  #include <linux/slab.h>
>  #include <linux/io.h>
>  #include "../../firmware/dcdbas.h"
> @@ -39,7 +41,11 @@ static DEFINE_MUTEX(buffer_mutex);
>  static int da_command_address;
>  static int da_command_code;
>  static int da_num_tokens;
> +static struct platform_device *platform_device;
>  static struct calling_interface_token *da_tokens;
> +static struct device_attribute *token_location_attrs;
> +static struct device_attribute *token_value_attrs;
> +static struct attribute **token_attrs;
>  
>  int dell_smbios_error(int value)
>  {
> @@ -157,6 +163,26 @@ static void __init parse_da_table(const struct dmi_header *dm)
>  	da_num_tokens += tokens;
>  }
>  
> +static void zero_duplicates(struct device *dev)
> +{
> +	int i, j;
> +
> +	for (i = 0; i < da_num_tokens; i++) {
> +		for (j = i+1; j < da_num_tokens; j++) {
> +			if (da_tokens[i].tokenID == 0 ||

Hint: you can move this check out of j-loop as condition is independent
of it.

Also how many tokens are there? Is not quadratic solution too slow?

> +			    da_tokens[j].tokenID == 0)
> +				continue;
> +			if (da_tokens[i].tokenID == da_tokens[j].tokenID) {
> +				dev_dbg(dev, "Zeroing dup token ID %x(%x/%x)\n",
> +					da_tokens[j].tokenID,
> +					da_tokens[j].location,
> +					da_tokens[j].value);
> +				da_tokens[j].tokenID = 0;
> +			}
> +		}
> +	}
> +}
> +
>  static void __init find_tokens(const struct dmi_header *dm, void *dummy)
>  {
>  	switch (dm->type) {
> @@ -170,6 +196,154 @@ static void __init find_tokens(const struct dmi_header *dm, void *dummy)
>  	}
>  }
>  
> +static int match_attribute(struct device *dev,
> +			   struct device_attribute *attr)
> +{
> +	int i;
> +
> +	for (i = 0; i < da_num_tokens * 2; i++) {
> +		if (!token_attrs[i])
> +			continue;
> +		if (strcmp(token_attrs[i]->name, attr->attr.name) == 0)
> +			return i/2;
> +	}
> +	dev_dbg(dev, "couldn't match: %s\n", attr->attr.name);
> +	return -EINVAL;
> +}
> +
> +static ssize_t location_show(struct device *dev,
> +			     struct device_attribute *attr, char *buf)
> +{
> +	int i;
> +
> +	if (!capable(CAP_SYS_ADMIN))
> +		return -EPERM;
> +
> +	i = match_attribute(dev, attr);
> +	if (i > 0)
> +		return scnprintf(buf, PAGE_SIZE, "%08x", da_tokens[i].location);
> +	return 0;
> +}
> +
> +static ssize_t value_show(struct device *dev,
> +			  struct device_attribute *attr, char *buf)
> +{
> +	int i;
> +
> +	if (!capable(CAP_SYS_ADMIN))
> +		return -EPERM;
> +
> +	i = match_attribute(dev, attr);
> +	if (i > 0)
> +		return scnprintf(buf, PAGE_SIZE, "%08x", da_tokens[i].value);
> +	return 0;
> +}
> +
> +static struct attribute_group smbios_attribute_group = {
> +	.name = "tokens"
> +};
> +
> +static struct platform_driver platform_driver = {
> +	.driver = {
> +		.name = "dell-smbios",
> +	},
> +};
> +
> +static int build_tokens_sysfs(struct platform_device *dev)
> +{
> +	char buffer_location[13];
> +	char buffer_value[10];
> +	char *location_name;
> +	char *value_name;
> +	size_t size;
> +	int ret;
> +	int i, j;
> +
> +	/* (number of tokens  + 1 for null terminated */
> +	size = sizeof(struct device_attribute) * (da_num_tokens + 1);
> +	token_location_attrs = kzalloc(size, GFP_KERNEL);
> +	if (!token_location_attrs)
> +		return -ENOMEM;
> +	token_value_attrs = kzalloc(size, GFP_KERNEL);
> +	if (!token_value_attrs)
> +		goto out_allocate_value;
> +
> +	/* need to store both location and value + terminator*/
> +	size = sizeof(struct attribute *) * ((2 * da_num_tokens) + 1);
> +	token_attrs = kzalloc(size, GFP_KERNEL);
> +	if (!token_attrs)
> +		goto out_allocate_attrs;
> +
> +	for (i = 0, j = 0; i < da_num_tokens; i++) {
> +		/* skip empty */
> +		if (da_tokens[i].tokenID == 0)
> +			continue;
> +		/* add location */
> +		sprintf(buffer_location, "%04x_location",
> +			da_tokens[i].tokenID);
> +		location_name = kstrdup(buffer_location, GFP_KERNEL);
> +		if (location_name == NULL)
> +			goto out_unwind_strings;
> +		sysfs_attr_init(&token_location_attrs[i].attr);
> +		token_location_attrs[i].attr.name = location_name;
> +		token_location_attrs[i].attr.mode = 0444;
> +		token_location_attrs[i].show = location_show;
> +		token_attrs[j++] = &token_location_attrs[i].attr;
> +
> +		/* add value */
> +		sprintf(buffer_value, "%04x_value",
> +			da_tokens[i].tokenID);
> +		value_name = kstrdup(buffer_value, GFP_KERNEL);
> +		if (value_name == NULL)
> +			goto loop_fail_create_value;
> +		sysfs_attr_init(&token_value_attrs[i].attr);
> +		token_value_attrs[i].attr.name = value_name;
> +		token_value_attrs[i].attr.mode = 0444;
> +		token_value_attrs[i].show = value_show;
> +		token_attrs[j++] = &token_value_attrs[i].attr;
> +		continue;
> +
> +loop_fail_create_value:
> +		kfree(value_name);
> +		goto out_unwind_strings;
> +	}
> +	smbios_attribute_group.attrs = token_attrs;
> +
> +	ret = sysfs_create_group(&dev->dev.kobj, &smbios_attribute_group);
> +	if (ret)
> +		goto out_unwind_strings;
> +	return 0;
> +
> +out_unwind_strings:
> +	for (i = i-1; i > 0; i--) {
> +		kfree(token_location_attrs[i].attr.name);
> +		kfree(token_value_attrs[i].attr.name);
> +	}
> +	kfree(token_attrs);
> +out_allocate_attrs:
> +	kfree(token_value_attrs);
> +out_allocate_value:
> +	kfree(token_location_attrs);
> +
> +	return -ENOMEM;
> +}
> +
> +static void free_group(struct platform_device *pdev)
> +{
> +	int i;
> +
> +	sysfs_remove_group(&pdev->dev.kobj,
> +				&smbios_attribute_group);
> +	for (i = 0; i < da_num_tokens; i++) {
> +		kfree(token_location_attrs[i].attr.name);
> +		kfree(token_value_attrs[i].attr.name);
> +	}
> +	kfree(token_attrs);
> +	kfree(token_value_attrs);
> +	kfree(token_location_attrs);
> +}
> +
> +
>  static int __init dell_smbios_init(void)
>  {
>  	const struct dmi_device *valid;
> @@ -197,9 +371,40 @@ static int __init dell_smbios_init(void)
>  		ret = -ENOMEM;
>  		goto fail_buffer;
>  	}
> +	ret = platform_driver_register(&platform_driver);
> +	if (ret)
> +		goto fail_platform_driver;
> +
> +	platform_device = platform_device_alloc("dell-smbios", 0);
> +	if (!platform_device) {
> +		ret = -ENOMEM;
> +		goto fail_platform_device_alloc;
> +	}
> +	ret = platform_device_add(platform_device);
> +	if (ret)
> +		goto fail_platform_device_add;
> +
> +	/* duplicate tokens will cause problems building sysfs files */
> +	zero_duplicates(&platform_device->dev);
> +
> +	ret = build_tokens_sysfs(platform_device);
> +	if (ret)
> +		goto fail_create_group;
>  
>  	return 0;
>  
> +fail_create_group:
> +	platform_device_del(platform_device);
> +
> +fail_platform_device_add:
> +	platform_device_put(platform_device);
> +
> +fail_platform_device_alloc:
> +	platform_driver_unregister(&platform_driver);
> +
> +fail_platform_driver:
> +	free_page((unsigned long)buffer);
> +
>  fail_buffer:
>  	kfree(da_tokens);
>  	return ret;
> @@ -207,8 +412,13 @@ static int __init dell_smbios_init(void)
>  
>  static void __exit dell_smbios_exit(void)
>  {
> -	kfree(da_tokens);
> +	if (platform_device) {
> +		free_group(platform_device);
> +		platform_device_unregister(platform_device);
> +		platform_driver_unregister(&platform_driver);
> +	}
>  	free_page((unsigned long)buffer);
> +	kfree(da_tokens);
>  }
>  
>  subsys_initcall(dell_smbios_init);

-- 
Pali Rohár
pali.rohar@gmail.com