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.limoncie...@dell.com>
> Reviewed-by: Edward O'Callaghan <quasi...@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.limoncie...@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" <ma...@linux-mips.org>
> S: Maintained
> F: drivers/net/fddi/defxx.*
>
> +DELL SMBIOS DRIVER
> +M: Pali Rohár <pali.ro...@gmail.com>
> +M: Mario Limonciello <mario.limoncie...@dell.com>
> +L: platform-driver-...@vger.kernel.org
> +S: Maintained
> +F: drivers/platform/x86/dell-smbios.*
> +
> DELL LAPTOP DRIVER
> M: Matthew Garrett <mj...@srcf.ucam.org>
> M: Pali Rohár <pali.ro...@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.ro...@gmail.com
