Re: [PATCH v12 10/13] HP BIOSCFG driver - spmobj-attributes

Ilpo Järvinen
2023-05-09T13:48:53Z

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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/spmobj-attributes.c | 381 ++++++++++++++++++
> 1 file changed, 381 insertions(+)
> create mode 100644 drivers/platform/x86/hp/hp-bioscfg/spmobj-attributes.c
>
> diff --git a/drivers/platform/x86/hp/hp-bioscfg/spmobj-attributes.c b/drivers/platform/x86/hp/hp-bioscfg/spmobj-attributes.c
> new file mode 100644
> index 000000000000..f08f7aae9423
> --- /dev/null
> +++ b/drivers/platform/x86/hp/hp-bioscfg/spmobj-attributes.c
> @@ -0,0 +1,381 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Functions corresponding to secure platform management object type
> + * attributes under BIOS PASSWORD for use with hp-bioscfg driver
> + *
> + * Copyright (c) 2022 HP Development Company, L.P.
> + */
> +
> +#include "bioscfg.h"
> +
> +static const char * const spm_state_types[] = {
> + "not provisioned",
> + "provisioned",
> + "provisioning in progress",
> +};
> +
> +static const char * const spm_mechanism_types[] = {
> + "not provisioned",
> + "signing-key",
> + "endorsement-key",
> +};
> +
> +struct secureplatform_provisioning_data {
> + u8 state;
> + u8 version[2];
> + u8 reserved1;
> + u32 features;
> + u32 nonce;
> + u8 reserved2[28];
> + u8 sk_mod[MAX_KEY_MOD];
> + u8 kek_mod[MAX_KEY_MOD];
> +};
> +
> +int check_spm_is_enabled(void)
> +{
> + /* do we need to check the admin password is also configured */
> + return bioscfg_drv.spm_data.is_enabled;
> +}
> +
> +/**
> + * calculate_security_buffer() - determines size of security buffer
> + * for authentication scheme
> + *
> + * @authentication: the authentication content
> + *
> + * Currently only supported type is Admin password
> + */
> +size_t calculate_security_buffer(const char *authentication)
> +{
> + int size;

Why not size_t?

> +
> + if (authentication && strlen(authentication) > 0) {
> + size = sizeof(u16) + (strlen(authentication) * sizeof(u16));

Extra parenthesis.

> + if (!strstarts(authentication, BEAM_PREFIX))
> + size += strlen(UTF_PREFIX) * sizeof(u16);
> +
> + return size;
> + }
> +
> + size = sizeof(u16) * 2;

Extra space

> + return size;

I'd do it this way though:

size_t size, authlen;

if (!authentication)
return sizeof(u16) * 2;

authlen = strlen(authentication);
if (!authlen)
return sizeof(u16) * 2;

size = sizeof(u16) + authlen * sizeof(u16);
...

> +}
> +
> +/**
> + * populate_security_buffer() - builds a security buffer for
> + * authentication scheme
> + *
> + * @buffer: the buffer to populate
> + * @authentication: the authentication content
> + *
> + * Currently only supported type is PLAIN TEXT
> + */
> +int populate_security_buffer(u16 *buffer, const char *authentication)
> +{
> + u16 *auth = buffer;
> + u16 *retbuffer;
> + char *strprefix = NULL;
> + int ret = 0;
> +
> + if (strstarts(authentication, BEAM_PREFIX)) {
> + /*
> + * BEAM_PREFIX is append to buffer when a signature
> + * is provided and Sure Admin is enabled in BIOS
> + */
> + // BEAM_PREFIX found, convert part to unicode
> + retbuffer = hp_ascii_to_utf16_unicode(auth, authentication);
> + if (!retbuffer) {
> + ret = -EINVAL;
> + goto out_buffer;

return -EINVAL directly.

> + }
> + auth = retbuffer;
> +
> + } else {
> + /*
> + * UTF-16 prefix is append to the * buffer when a BIOS

What is "the * buffer" ?

> + * admin password is configured in BIOS
> + */
> +
> + // append UTF_PREFIX to part and then convert it to unicode

Use /* */ comments consistently.

> + strprefix = kasprintf(GFP_KERNEL, "%s%s", UTF_PREFIX,
> + authentication);
> + if (!strprefix)
> + goto out_buffer;

Shouldn't you return an error code here? Also, strprefix is NULL so you
can do return -ENOMEM directly.

> +
> + retbuffer = hp_ascii_to_utf16_unicode(auth, strprefix);

If you move kfree(strprefix) here, the flow is more obvious.

> + if (!retbuffer) {
> + ret = -EINVAL;
> + goto out_buffer;
> + }
> + auth = retbuffer;
> + }
> +
> +out_buffer:
> + kfree(strprefix);
> + return ret;
> +}
> +
> +static ssize_t update_spm_state(void)
> +{
> + int ret;
> + struct secureplatform_provisioning_data data;
> +
> + ret = hp_wmi_perform_query(HPWMI_SECUREPLATFORM_GET_STATE,
> + HPWMI_SECUREPLATFORM, &data, 0,
> + sizeof(data));
> + if (ret < 0)
> + goto state_exit;

return ret; directly.

> +
> + bioscfg_drv.spm_data.mechanism = data.state;
> + if (bioscfg_drv.spm_data.mechanism)
> + bioscfg_drv.spm_data.is_enabled = 1;
> +
> +state_exit:
> + return ret;

return 0;

> +}
> +
> +static ssize_t statusbin(struct kobject *kobj,
> + struct kobj_attribute *attr,
> + struct secureplatform_provisioning_data *buf)
> +{
> + int ret = hp_wmi_perform_query(HPWMI_SECUREPLATFORM_GET_STATE,
> + HPWMI_SECUREPLATFORM, buf, 0,
> + sizeof(struct secureplatform_provisioning_data));
> +
> + return ret < 0 ? ret : sizeof(struct secureplatform_provisioning_data);

Split to:

int ret;

ret = hp_...();
if (ret < 0)
return ret;

return sizeof(...);

> +}
> +
> +/*
> + * status_show - Reads SPM status
> + */
> +static ssize_t status_show(struct kobject *kobj, struct kobj_attribute
> + *attr, char *buf)
> +{
> + int ret, i;
> + struct secureplatform_provisioning_data data;
> +
> + ret = statusbin(kobj, attr, &data);
> + if (ret < 0)
> + goto status_exit;

Can you calculate strnlen() from buf at this point, or is the result
garbage? Should you return ret instead here?

> +
> + sysfs_emit(buf, "%s{\n", buf);
> + sysfs_emit(buf, "%s\t\"State\": \"%s\",\n", buf,
> + spm_state_types[data.state]);
> + sysfs_emit(buf, "%s\t\"Version\": \"%d.%d\",\n", buf, data.version[0],
> + data.version[1]);
> +
> + /*
> + * state == 0 means secure platform management
> + * feature is not configured in BIOS.
> + */
> + if (data.state == 0)
> + goto status_exit;
> +
> + sysfs_emit(buf, "%s\t\"Nonce\": %d,\n", buf, data.nonce);
> + sysfs_emit(buf, "%s\t\"FeaturesInUse\": %d,\n", buf, data.features);
> + sysfs_emit(buf, "%s\t\"EndorsementKeyMod\": \"", buf);
> +
> + for (i = 255; i >= 0; i--)
> + sysfs_emit(buf, "%s %u", buf, data.kek_mod[i]);
> +
> + sysfs_emit(buf, "%s \",\n", buf);
> + sysfs_emit(buf, "%s\t\"SigningKeyMod\": \"", buf);
> +
> + for (i = 255; i >= 0; i--)
> + sysfs_emit(buf, "%s %u", buf, data.sk_mod[i]);
> +
> + /* Return buf contents */
> +
> + sysfs_emit(buf, "%s \"\n", buf);
> + sysfs_emit(buf, "%s}\n", buf);
> +
> +status_exit:
> + return strnlen(buf, PAGE_SIZE);
> +}

Emit buf into buf? There's sysfs_emit_at(), however,

while I'm far from sysfs formatting expert, this feels something that
tries to expose more than one thing over same sysfs file. Shouldn't they
be each in their own files?

> +static struct kobj_attribute password_spm_status = __ATTR_RO(status);
> +
> +ATTRIBUTE_SPM_N_PROPERTY_SHOW(is_enabled, spm);
> +static struct kobj_attribute password_spm_is_key_enabled = __ATTR_RO(is_enabled);
> +
> +static ssize_t key_mechanism_show(struct kobject *kobj, struct kobj_attribute *attr,
> + char *buf)
> +{
> + return sysfs_emit(buf, "%s\n",
> + spm_mechanism_types[bioscfg_drv.spm_data.mechanism]);
> +}
> +
> +static struct kobj_attribute password_spm_key_mechanism = __ATTR_RO(key_mechanism);
> +
> +static ssize_t sk_store(struct kobject *kobj,
> + struct kobj_attribute *attr,
> + const char *buf, size_t count)
> +{
> + int ret;
> + int length;
> +
> + length = count;
> + if (buf[length - 1] == '\n')
> + length--;
> +
> + /* allocate space and copy current signing key */
> + bioscfg_drv.spm_data.signing_key = kmalloc(length, GFP_KERNEL);
> + if (!bioscfg_drv.spm_data.signing_key) {
> + ret = -ENOMEM;
> + goto exit_sk;
> + }
> +
> + strscpy(bioscfg_drv.spm_data.signing_key, buf, length);
> + bioscfg_drv.spm_data.signing_key[length] = '\0';
> +
> + /* submit signing key payload */
> + ret = hp_wmi_perform_query(HPWMI_SECUREPLATFORM_SET_SK,
> + HPWMI_SECUREPLATFORM,
> + (void *)bioscfg_drv.spm_data.signing_key,
> + length, 0);
> +
> + if (!ret) {
> + bioscfg_drv.spm_data.mechanism = SIGNING_KEY;
> + set_reboot_and_signal_event();
> + }
> +
> +exit_sk:
> + kfree(bioscfg_drv.spm_data.signing_key);
> + bioscfg_drv.spm_data.signing_key = NULL;
> +
> + return ret ? ret : count;
> +}
> +
> +static struct kobj_attribute password_spm_signing_key = __ATTR_WO(sk);
> +
> +static ssize_t kek_store(struct kobject *kobj,
> + struct kobj_attribute *attr,
> + const char *buf, size_t count)
> +{
> + int ret;
> + int length;
> +
> + length = count;
> + if (buf[length - 1] == '\n')
> + length--;
> +
> + /* allocate space and copy current signing key */
> + bioscfg_drv.spm_data.endorsement_key = kmalloc(length, GFP_KERNEL);
> + if (!bioscfg_drv.spm_data.endorsement_key) {
> + ret = -ENOMEM;
> + goto exit_kek;

Return directly.

> + }
> +
> + memcpy(bioscfg_drv.spm_data.endorsement_key, buf, length);
> + bioscfg_drv.spm_data.endorsement_key[length] = '\0';
> +
> + ret = hp_wmi_perform_query(HPWMI_SECUREPLATFORM_SET_KEK,
> + HPWMI_SECUREPLATFORM,
> + (void *)bioscfg_drv.spm_data.endorsement_key,

In general, casting to void * (and back) is not required.

> + count, 0);
> +
> + if (!ret) {
> + bioscfg_drv.spm_data.mechanism = ENDORSEMENT_KEY;
> + set_reboot_and_signal_event();
> + }
> +
> +exit_kek:
> + kfree(bioscfg_drv.spm_data.endorsement_key);
> + bioscfg_drv.spm_data.endorsement_key = NULL;
> +
> + return ret ? ret : count;
> +}
> +
> +static struct kobj_attribute password_spm_endorsement_key = __ATTR_WO(kek);
> +
> +static ssize_t role_show(struct kobject *kobj, struct kobj_attribute *attr,
> + char *buf)
> +{
> + return sysfs_emit(buf, "%s\n", BIOS_SPM);
> +}
> +
> +static struct kobj_attribute password_spm_role = __ATTR_RO(role);
> +
> +static ssize_t auth_token_store(struct kobject *kobj,
> + struct kobj_attribute *attr,
> + const char *buf, size_t count)
> +{
> + int ret = 0;
> + int length;
> +
> + length = count;
> + if (buf[length - 1] == '\n')
> + length--;
> +
> + /* allocate space and copy current auth token */
> + bioscfg_drv.spm_data.auth_token = kmalloc(count, GFP_KERNEL);
> + if (!bioscfg_drv.spm_data.auth_token) {
> + ret = -ENOMEM;
> + goto exit_token;

Return directly.

> + }
> +
> + memcpy(bioscfg_drv.spm_data.auth_token, buf, count);
> + bioscfg_drv.spm_data.auth_token[length] = '\0';
> + return count;
> +
> +exit_token:
> + kfree(bioscfg_drv.spm_data.auth_token);
> + bioscfg_drv.spm_data.auth_token = NULL;
> +
> + return ret;
> +}
> +
> +static struct kobj_attribute password_spm_auth_token = __ATTR_WO(auth_token);
> +
> +static struct attribute *secure_platform_attrs[] = {
> + &password_spm_is_key_enabled.attr,
> + &password_spm_signing_key.attr,
> + &password_spm_endorsement_key.attr,
> + &password_spm_key_mechanism.attr,
> + &password_spm_status.attr,
> + &password_spm_role.attr,
> + &password_spm_auth_token.attr,
> + NULL,
> +};
> +
> +static const struct attribute_group secure_platform_attr_group = {
> + .attrs = secure_platform_attrs,
> +};
> +
> +void exit_secure_platform_attributes(void)
> +{
> + /* remove secure platform sysfs entry and free key data*/
> +
> + kfree(bioscfg_drv.spm_data.endorsement_key);
> + bioscfg_drv.spm_data.endorsement_key = NULL;
> +
> + kfree(bioscfg_drv.spm_data.signing_key);
> + bioscfg_drv.spm_data.signing_key = NULL;
> +
> + kfree(bioscfg_drv.spm_data.auth_token);
> + bioscfg_drv.spm_data.auth_token = NULL;
> +
> + if (bioscfg_drv.spm_data.attr_name_kobj)
> + sysfs_remove_group(bioscfg_drv.spm_data.attr_name_kobj,
> + &secure_platform_attr_group);
> +}
> +
> +int populate_secure_platform_data(struct kobject *attr_name_kobj)
> +{
> + /* Populate data for Secure Platform Management */
> + bioscfg_drv.spm_data.attr_name_kobj = attr_name_kobj;
> +
> + strscpy(bioscfg_drv.spm_data.attribute_name, SPM_STR,
> + sizeof(bioscfg_drv.spm_data.attribute_name));
> +
> + bioscfg_drv.spm_data.is_enabled = 0;
> + bioscfg_drv.spm_data.mechanism = 0;
> + bioscfg_drv.pending_reboot = false;
> + update_spm_state();
> +
> + bioscfg_drv.spm_data.endorsement_key = NULL;
> + bioscfg_drv.spm_data.signing_key = NULL;
> + bioscfg_drv.spm_data.auth_token = NULL;
> +
> + return sysfs_create_group(attr_name_kobj, &secure_platform_attr_group);
> +}
>

--
i.