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

[Sathyanarayanan Kuppuswamy]

Hi Rafael,

On 3/20/23 10:15 AM, Rafael J. Wysocki wrote:
> On Thu, Mar 2, 2023 at 8:13 AM Kuppuswamy Sathyanarayanan
> <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx> 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@xxxxxxxxx>
>> [Original patch is for TDEL table, modified it for CCEL support]
>> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
>> ---
>>  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.

Yes. We can do without it. Shall I submit v2 with this change, or you want to
fix it when applying?

> 
>> +               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