linux-kernel - Re: [PATCH v1] ACPI: sysfs: Enable ACPI sysfs support for CCEL records

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Date:   Wed, 15 Mar 2023 13:48:56 -0700
From:   Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Rafael J Wysocki <rjw@...ysocki.net>
Cc:     Len Brown <lenb@...nel.org>, linux-acpi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] ACPI: sysfs: Enable ACPI sysfs support for CCEL
 records

Hi Rafael,

Gentle ping! Any comments on this patch?

On 3/1/23 11:13 PM, Kuppuswamy Sathyanarayanan wrote:
> The Confidential Computing Event Log (CCEL) table provides the address
> and length of the CCEL records area in UEFI reserved memory. To access
> these records, userspace can use /dev/mem to retrieve them. But
> '/dev/mem' is not enabled on many systems for security reasons.
> 
> So to allow user space access these event log records without the
> /dev/mem interface, add support to access it via sysfs interface. The
> ACPI driver has provided read only access to BERT records area via
> '/sys/firmware/acpi/tables/data/BERT' in sysfs. So follow the same way,
> and add support for /sys/firmware/acpi/tables/data/CCEL to enable
> read-only access to the CCEL recorids area.
> 
> More details about the CCEL table can be found in ACPI specification
> r6.5, sec titled "CC Event Log ACPI Table".
> 
> Original-patch-by: Haibo Xu <haibo1.xu@...el.com>
> [Original patch is for TDEL table, modified it for CCEL support]
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> ---
>  drivers/acpi/sysfs.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/drivers/acpi/sysfs.c b/drivers/acpi/sysfs.c
> index 7db3b530279b..afeac925b31b 100644
> --- a/drivers/acpi/sysfs.c
> +++ b/drivers/acpi/sysfs.c
> @@ -458,11 +458,28 @@ static int acpi_bert_data_init(void *th, struct acpi_data_attr *data_attr)
>  	return sysfs_create_bin_file(tables_data_kobj, &data_attr->attr);
>  }
>  
> +static int acpi_ccel_data_init(void *th, struct acpi_data_attr *data_attr)
> +{
> +	struct acpi_table_ccel *ccel = th;
> +
> +	if (ccel->header.length < sizeof(struct acpi_table_ccel) ||
> +	    !(ccel->log_area_start_address) || !(ccel->log_area_minimum_length)) {
> +		kfree(data_attr);
> +		return -EINVAL;
> +	}
> +	data_attr->addr = ccel->log_area_start_address;
> +	data_attr->attr.size = ccel->log_area_minimum_length;
> +	data_attr->attr.attr.name = "CCEL";
> +
> +	return sysfs_create_bin_file(tables_data_kobj, &data_attr->attr);
> +}
> +
>  static struct acpi_data_obj {
>  	char *name;
>  	int (*fn)(void *, struct acpi_data_attr *);
>  } acpi_data_objs[] = {
>  	{ ACPI_SIG_BERT, acpi_bert_data_init },
> +	{ ACPI_SIG_CCEL, acpi_ccel_data_init },
>  };
>  
>  #define NUM_ACPI_DATA_OBJS ARRAY_SIZE(acpi_data_objs)

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer