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

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Message-ID: <CAJZ5v0gB7WSB3F3+kTnB-r83xO9G7Sk1Vyh2os0=AeYNvHK_Mw@mail.gmail.com>
Date:   Mon, 20 Mar 2023 18:15:32 +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 v1] ACPI: sysfs: Enable ACPI sysfs support for CCEL records

On Thu, Mar 2, 2023 at 8:13 AM 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. 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)) {

The inner parens in this line are not necessary AFAICS.

Otherwise I have no objections.

> +               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)
> --