Re: [PATCH v12 02/13] HP BIOSCFG driver - biosattr-interface

Ilpo Järvinen
2023-05-08T14:34:11Z

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On Fri, 5 May 2023, Jorge Lopez wrote:

> HP BIOS Configuration driver purpose is to provide a driver supporting
> the latest sysfs class firmware attributes framework allowing the user
> to change BIOS settings and security solutions on HP Inc.’s commercial
> notebooks.
>
> Many features of HP Commercial notebooks can be managed using Windows
> Management Instrumentation (WMI). WMI is an implementation of Web-Based
> Enterprise Management (WBEM) that provides a standards-based interface
> for changing and monitoring system settings. HP BIOSCFG driver provides
> a native Linux solution and the exposed features facilitates the
> migration to Linux environments.
>
> The Linux security features to be provided in hp-bioscfg driver enables
> managing the BIOS settings and security solutions via sysfs, a virtual
> filesystem that can be used by user-mode applications. The new
> documentation cover HP-specific firmware sysfs attributes such Secure
> Platform Management and Sure Start. Each section provides security
> feature description and identifies sysfs directories and files exposed
> by the driver.
>
> Many HP Commercial notebooks include a feature called Secure Platform
> Management (SPM), which replaces older password-based BIOS settings
> management with public key cryptography. PC secure product management
> begins when a target system is provisioned with cryptographic keys
> that are used to ensure the integrity of communications between system
> management utilities and the BIOS.
>
> HP Commercial notebooks have several BIOS settings that control its
> behaviour and capabilities, many of which are related to security.
> To prevent unauthorized changes to these settings, the system can
> be configured to use a cryptographic signature-based authorization
> string that the BIOS will use to verify authorization to modify the
> setting.
>
> Linux Security components are under development and not published yet.
> The only linux component is the driver (hp bioscfg) at this time.
> Other published security components are under Windows.
>
> Signed-off-by: Jorge Lopez <jorge.lopez2@hp.com>
>
> ---
> Based on the latest platform-drivers-x86.git/for-next
> ---
> .../x86/hp/hp-bioscfg/biosattr-interface.c | 319 ++++++++++++++++++
> 1 file changed, 319 insertions(+)
> create mode 100644 drivers/platform/x86/hp/hp-bioscfg/biosattr-interface.c
>
> diff --git a/drivers/platform/x86/hp/hp-bioscfg/biosattr-interface.c b/drivers/platform/x86/hp/hp-bioscfg/biosattr-interface.c
> new file mode 100644
> index 000000000000..8f7039a4416a
> --- /dev/null
> +++ b/drivers/platform/x86/hp/hp-bioscfg/biosattr-interface.c
> @@ -0,0 +1,319 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Functions corresponding to methods under BIOS interface GUID
> + * for use with hp-bioscfg driver.
> + *
> + * Copyright (c) 2022 Hewlett-Packard Inc.
> + */
> +
> +#include <linux/wmi.h>
> +#include "bioscfg.h"
> +
> +/*
> + * struct bios_args buffer is dynamically allocated. New WMI command types
> + * were introduced that exceeds 128-byte data size. Changes to handle
> + * the data size allocation scheme were kept in hp_wmi_perform_query function.
> + */
> +struct bios_args {
> + u32 signature;
> + u32 command;
> + u32 commandtype;
> + u32 datasize;
> + u8 data[];
> +};
> +
> +/**
> + * hp_set_attribute
> + *
> + * @a_name: The attribute name
> + * @a_value: The attribute value
> + *
> + * Sets an attribute to new value
> + *
> + * Returns zero on success
> + * -ENODEV if device is not found
> + * -EINVAL if the instance of 'Setup Admin' password is not found.
> + * -ENOMEM unable to allocate memory

Inconsistent indent.

> + */
> +int hp_set_attribute(const char *a_name, const char *a_value)
> +{
> + size_t security_area_size;
> + size_t a_name_size, a_value_size;
> + u16 *buffer = NULL;
> + u16 *start;
> + int buffer_size, instance, ret;
> + char *auth_token_choice;
> + u16 *retbuffer;
> +
> + mutex_lock(&bioscfg_drv.mutex);
> + if (!bioscfg_drv.bios_attr_wdev) {
> + ret = -ENODEV;
> + goto out_set_attribute;
> + }
> +
> + instance = get_password_instance_for_type(SETUP_PASSWD);
> + if (instance < 0) {
> + ret = -EINVAL;
> + goto out_set_attribute;
> + }
> +
> + /* Select which auth token to use; password or [auth token] */
> +

Remove newline

> + if (bioscfg_drv.spm_data.auth_token)
> + auth_token_choice = bioscfg_drv.spm_data.auth_token;
> + else
> + auth_token_choice = bioscfg_drv.password_data[instance].current_password;
> +
> + a_name_size = hp_calculate_string_buffer(a_name);
> + a_value_size = hp_calculate_string_buffer(a_value);
> + security_area_size = calculate_security_buffer(auth_token_choice);
> + buffer_size = a_name_size + a_value_size + security_area_size;
> +
> + buffer = kmalloc(buffer_size + 1, GFP_KERNEL);
> + if (!buffer) {
> + ret = -ENOMEM;
> + goto out_set_attribute;
> + }
> +
> + /* build variables to set */
> + start = buffer;
> + retbuffer = hp_ascii_to_utf16_unicode(start, a_name);
> + if (!retbuffer) {
> + ret = -EINVAL;
> + goto out_set_attribute;
> + }
> + start = retbuffer;
> +
> + retbuffer = hp_ascii_to_utf16_unicode(start, a_value);
> + if (!retbuffer) {
> + ret = -EINVAL;
> + goto out_set_attribute;
> + }
> + start = retbuffer;
> +
> + ret = populate_security_buffer(start, auth_token_choice);
> + if (ret < 0)
> + goto out_set_attribute;
> +
> + ret = hp_wmi_set_bios_setting(buffer, buffer_size);
> +
> +out_set_attribute:
> + kfree(buffer);
> + mutex_unlock(&bioscfg_drv.mutex);
> + return ret;
> +}
> +
> +/**
> + * hp_wmi_perform_query
> + *
> + * @query: The commandtype (enum hp_wmi_commandtype)
> + * @command: The command (enum hp_wmi_command)
> + * @buffer: Buffer used as input and/or output
> + * @insize: Size of input buffer
> + * @outsize: Size of output buffer
> + *
> + * returns zero on success
> + * an HP WMI query specific error code (which is positive)
> + * -EINVAL if the query was not successful at all
> + * -EINVAL if the output buffer size exceeds buffersize
> + *
> + * Note: The buffersize must at least be the maximum of the input and output
> + * size. E.g. Battery info query is defined to have 1 byte input
> + * and 128 byte output. The caller would do:
> + * buffer = kzalloc(128, GFP_KERNEL);
> + * ret = hp_wmi_perform_query(HPWMI_BATTERY_QUERY, HPWMI_READ,
> + * buffer, 1, 128)
> + */
> +int hp_wmi_perform_query(int query, enum hp_wmi_command command, void *buffer,
> + u32 insize, u32 outsize)
> +{
> + struct acpi_buffer input, output = { ACPI_ALLOCATE_BUFFER, NULL };
> + struct bios_return *bios_return;
> + union acpi_object *obj = NULL;
> + struct bios_args *args = NULL;
> + u32 mid, actual_outsize, ret;
> + size_t bios_args_size;
> +
> + mid = encode_outsize_for_pvsz(outsize);
> + if (WARN_ON(mid < 0))
> + return mid;
> +
> + bios_args_size = struct_size(args, data, insize);
> + args = kmalloc(bios_args_size, GFP_KERNEL);
> + if (!args)
> + return -ENOMEM;
> +
> + input.length = bios_args_size;
> + input.pointer = args;
> +
> + /* BIOS expects 'SECU' in hex as the signature value*/
> + args->signature = 0x55434553;
> + args->command = command;
> + args->commandtype = query;
> + args->datasize = insize;
> + memcpy(args->data, buffer, flex_array_size(args, data, insize));
> +
> + ret = wmi_evaluate_method(HP_WMI_BIOS_GUID, 0, mid, &input, &output);
> + hp_wmi_error_and_message(ret);
> +
> + if (ret)
> + goto out_free;
> +
> + obj = output.pointer;
> + if (!obj) {
> + ret = -EINVAL;
> + goto out_free;
> + }
> +
> + if (obj->type != ACPI_TYPE_BUFFER ||
> + obj->buffer.length < sizeof(*bios_return)) {
> + pr_warn("query 0x%x returned wrong type or too small buffer\n", query);
> + ret = -EINVAL;
> + goto out_free;
> + }
> +
> + bios_return = (struct bios_return *)obj->buffer.pointer;
> + ret = bios_return->return_code;
> + hp_wmi_error_and_message(ret);
> +
> + if (ret) {
> + if (ret != INVALID_CMD_VALUE &&
> + ret != INVALID_CMD_TYPE)

To the same line.

> + pr_warn("query 0x%x returned error 0x%x\n", query, ret);
> + goto out_free;
> + }
> +
> + /* Ignore output data of zero size */
> + if (!outsize)
> + goto out_free;
> +
> + actual_outsize = min(outsize, (u32)(obj->buffer.length - sizeof(*bios_return)));

Use min_t() instead of casting.

> + memcpy_and_pad(buffer, outsize, obj->buffer.pointer + sizeof(*bios_return),
> + actual_outsize, 0);
> +
> +out_free:
> + kfree(obj);
> + kfree(args);
> + return ret;
> +}
> +
> +static void *utf16_empty_string(u16 *p)
> +{
> + *p++ = 2;
> + *p++ = (u8)0x00;

Useless and non-sensical cast.

> + return p;
> +}
> +
> +/**
> + * hp_ascii_to_utf16_unicode - Convert ascii string to UTF-16 unicode
> + *
> + * BIOS supports UTF-16 characters that are 2 bytes long. No variable
> + * multi-byte language supported.
> + *
> + * @p: Unicode buffer address
> + * @str: string to convert to unicode
> + *
> + * Returns a void pointer to the buffer string
> + */
> +void *hp_ascii_to_utf16_unicode(u16 *p, const u8 *str)
> +{
> + int len = strlen(str);
> + int ret;
> +
> + /*
> + * Add null character when reading an empty string
> + * "02 00 00 00"
> + */
> + if (len == 0)
> + return utf16_empty_string(p);
> +
> + /* Move pointer len * 2 number of bytes */
> + *p++ = len * 2;

The comment sounds odd given the code context here.

> + ret = utf8s_to_utf16s(str, strlen(str), UTF16_HOST_ENDIAN, p, len);

Why is strlen(str) recalculated here?

> + if (ret < 0) {
> + dev_err(bioscfg_drv.class_dev, "UTF16 conversion failed\n");
> + return NULL;
> + }
> +
> + if ((ret * sizeof(u16)) > U16_MAX) {

Unnecessary parenthesis.

> + dev_err(bioscfg_drv.class_dev, "Error string too long\n");
> + return NULL;
> + }
> +
> + p += len;

Is this correct ?

> + return p;
> +}
> +
> +/**
> + * hp_wmi_set_bios_setting - Set setting's value in BIOS
> + *
> + * @input_buffer: Input buffer address
> + * @input_size: Input buffer size
> + *
> + * Returns: Count of unicode characters written to BIOS if successful, otherwise
> + * -ENOMEM unable to allocate memory
> + * -EINVAL buffer not allocated or too small
> + */
> +int hp_wmi_set_bios_setting(u16 *input_buffer, u32 input_size)
> +{
> + union acpi_object *obj;
> + struct acpi_buffer input = {input_size, input_buffer};
> + struct acpi_buffer output = {ACPI_ALLOCATE_BUFFER, NULL};
> + int ret;
> +
> + ret = wmi_evaluate_method(HP_WMI_SET_BIOS_SETTING_GUID, 0, 1, &input, &output);
> +
> + obj = output.pointer;
> + if (!obj)
> + return -EINVAL;
> +
> + if (obj->type != ACPI_TYPE_INTEGER)
> + ret = -EINVAL;

Missing goto?

> +
> + ret = obj->integer.value;
> + hp_wmi_error_and_message(ret);
> +
> + kfree(obj);
> + return ret;
> +}

--
i.

> +
> +static int hp_attr_set_interface_probe(struct wmi_device *wdev, const void *context)
> +{
> + mutex_lock(&bioscfg_drv.mutex);
> + bioscfg_drv.bios_attr_wdev = wdev;
> + mutex_unlock(&bioscfg_drv.mutex);
> + return 0;
> +}
> +
> +static void hp_attr_set_interface_remove(struct wmi_device *wdev)
> +{
> + mutex_lock(&bioscfg_drv.mutex);
> + bioscfg_drv.bios_attr_wdev = NULL;
> + mutex_unlock(&bioscfg_drv.mutex);
> +}
> +
> +static const struct wmi_device_id hp_attr_set_interface_id_table[] = {
> + { .guid_string = HP_WMI_BIOS_GUID},
> + { }
> +};
> +
> +static struct wmi_driver hp_attr_set_interface_driver = {
> + .driver = {
> + .name = DRIVER_NAME,
> + },
> + .probe = hp_attr_set_interface_probe,
> + .remove = hp_attr_set_interface_remove,
> + .id_table = hp_attr_set_interface_id_table,
> +};
> +
> +int init_hp_attr_set_interface(void)
> +{
> + return wmi_driver_register(&hp_attr_set_interface_driver);
> +}
> +
> +void exit_hp_attr_set_interface(void)
> +{
> + wmi_driver_unregister(&hp_attr_set_interface_driver);
> +}
> +
> +MODULE_DEVICE_TABLE(wmi, hp_attr_set_interface_id_table);
>