linux-kernel - Re: [PATCH v2] ACPI: sysfs: Enable ACPI sysfs support for CCEL records

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Date:   Wed, 22 Mar 2023 19:31:24 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     Rafael J Wysocki <rjw@...ysocki.net>, Len Brown <lenb@...nel.org>,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] ACPI: sysfs: Enable ACPI sysfs support for CCEL records

On Mon, Mar 20, 2023 at 10:21 PM Kuppuswamy Sathyanarayanan
<sathyanarayanan.kuppuswamy@...ux.intel.com> wrote:
>
> The Confidential Computing Event Log (CCEL) table provides the address
> and length of the CCEL records area in UEFI reserved memory.

The rest of this paragraph can be omitted.

> 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".

Please provide a proper section number here and a Link: tag pointing
to the relevant section of the spec (which is
https://uefi.org/specs/ACPI/6.5/05_ACPI_Software_Programming_Model.html#cc-event-log-acpi-table
I think).

> Original-patch-by: Haibo Xu <haibo1.xu@...el.com>

If the original patch has been signed-off by that developer, you can
use a Co-developed-by: along with the original S-o-b tag here.

> [Original patch is for TDEL table, modified it for CCEL support]
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> ---
>
> Changes since v1:
>  * Removed unnecessary parenthesis as per Rafael's suggestion..
>
>  drivers/acpi/sysfs.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
>
> diff --git a/drivers/acpi/sysfs.c b/drivers/acpi/sysfs.c
> index 7f4ff56c9d42..687524b50085 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)
> --
> 2.34.1
>