Re: [PATCH v12 11/13] HP BIOSCFG driver - surestart-attributes

[Ilpo Järvinen]

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@xxxxxx>
> 
> ---
> Based on the latest platform-drivers-x86.git/for-next
> ---
>  .../x86/hp/hp-bioscfg/surestart-attributes.c  | 133 ++++++++++++++++++
>  1 file changed, 133 insertions(+)
>  create mode 100644 drivers/platform/x86/hp/hp-bioscfg/surestart-attributes.c
> 
> diff --git a/drivers/platform/x86/hp/hp-bioscfg/surestart-attributes.c b/drivers/platform/x86/hp/hp-bioscfg/surestart-attributes.c
> new file mode 100644
> index 000000000000..b627c324f6a6
> --- /dev/null
> +++ b/drivers/platform/x86/hp/hp-bioscfg/surestart-attributes.c
> @@ -0,0 +1,133 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Functions corresponding to sure start object type attributes under
> + * BIOS for use with hp-bioscfg driver
> + *
> + *  Copyright (c) 2022 HP Development Company, L.P.
> + */
> +
> +#include "bioscfg.h"
> +#include <linux/types.h>
> +
> +/* Maximum number of log entries supported when log entry size is 16
> + * bytes.  This value is calculated by dividing 4096 (page size) by
> + * log entry size.
> + */
> +#define LOG_MAX_ENTRIES		254
> +
> +/*
> + * Current Log entry size.  This value size will change in the
> + * future. The driver reads a total of 128 bytes for each log entry
> + * provided by BIOS but only the first 16 bytes are used/read.
> + */
> +#define LOG_ENTRY_SIZE		16
> +
> +/*
> + * audit_log_entry_count_show - Reports the number of
> + *				existing audit log entries available
> + *				to be read
> + */
> +static ssize_t audit_log_entry_count_show(struct kobject *kobj,
> +					  struct kobj_attribute *attr, char *buf)
> +{
> +	int ret;
> +	u32 count = 0;
> +
> +	ret = hp_wmi_perform_query(HPWMI_SURESTART_GET_LOG_COUNT,
> +				   HPWMI_SURESTART,
> +				   &count, 1, sizeof(count));
> +

Extra newline.

> +	if (ret < 0)
> +		return ret;
> +
> +	return sysfs_emit(buf, "%d,%d,%d\n", count, LOG_ENTRY_SIZE,
> +			  LOG_MAX_ENTRIES);

Why 3 values instead of 1?

> +}
> +
> +/*
> + * audit_log_entries_show() - Return all entries found in log file
> + */
> +static ssize_t audit_log_entries_show(struct kobject *kobj,
> +				      struct kobj_attribute *attr, char *buf)
> +{
> +	int ret;
> +	int i;
> +	u32 count = 0;
> +	u8 audit_log_buffer[128];
> +
> +	// Get the number of event logs
> +	ret = hp_wmi_perform_query(HPWMI_SURESTART_GET_LOG_COUNT,
> +				   HPWMI_SURESTART,
> +				   &count, 1, sizeof(count));
> +

Extra newline.

> +	if (ret < 0)
> +		return ret;
> +
> +	/*
> +	 * The show() api will not work if the audit logs ever go
> +	 *  beyond 4KB

Extra space.

> +	 */
> +	if (count * LOG_ENTRY_SIZE > PAGE_SIZE)
> +		return -EIO;
> +
> +	/*
> +	 * We are guaranteed the buffer is 4KB so today all the event
> +	 * logs will fit
> +	 */
> +	for (i = 0; i < count; i++) {
> +		audit_log_buffer[0] = (i + 1);

Extra parenthesis.

> +
> +		/*
> +		 * read audit log entry at a time. 'buf' input value
> +		 * provides  the audit log entry to be read.  On

Extra spaces.

> +		 * input, Byte 0 = Audit Log entry number from
> +		 * beginning (1..254)
> +		 * Entry number 1 is the newest entry whereas the
> +		 * highest entry number (number of entries) is the
> +		 * oldest entry.
> +		 */
> +		ret = hp_wmi_perform_query(HPWMI_SURESTART_GET_LOG,
> +					   HPWMI_SURESTART,
> +					   audit_log_buffer, 1, 128);
> +
> +		if (ret >= 0 && (LOG_ENTRY_SIZE * i) < PAGE_SIZE) {

Can the second condition ever fail?

> +			memcpy(buf, audit_log_buffer, LOG_ENTRY_SIZE);
> +			buf += LOG_ENTRY_SIZE;
> +		} else {
> +			/*
> +			 * Encountered a failure while reading
> +			 * individual logs. Only a partial list of
> +			 * audit log will be returned.
> +			 */
> +			count = i + 1;
> +			break;
> +		}

Reverse order, do error handling with break first.

Why not return i * LOG_ENTRY_SIZE directly (or at the end), no need to 
tweak count?

> +	}
> +
> +	return count * LOG_ENTRY_SIZE;
> +}
> +
> +static struct kobj_attribute sure_start_audit_log_entry_count = __ATTR_RO(audit_log_entry_count);
> +static struct kobj_attribute sure_start_audit_log_entries = __ATTR_RO(audit_log_entries);
> +
> +static struct attribute *sure_start_attrs[] = {
> +	&sure_start_audit_log_entry_count.attr,
> +	&sure_start_audit_log_entries.attr,
> +	NULL,
> +};
> +
> +static const struct attribute_group sure_start_attr_group = {
> +	.attrs = sure_start_attrs,
> +};
> +
> +void exit_sure_start_attributes(void)
> +{
> +	sysfs_remove_group(bioscfg_drv.sure_start_attr_kobj,
> +			   &sure_start_attr_group);
> +}
> +
> +int populate_sure_start_data(struct kobject *attr_name_kobj)
> +{
> +	bioscfg_drv.sure_start_attr_kobj = attr_name_kobj;
> +	return sysfs_create_group(attr_name_kobj, &sure_start_attr_group);
> +}
> 

-- 
 i.