[PATCH v2] ACPI: sysfs: Enable ACPI sysfs support for CCEL records

[Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>]

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@intel.com>
[Original patch is for TDEL table, modified it for CCEL support]
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.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