Add support for reading CCEL EventLogs from devmem (#288)

* Add support for reading CCEL EventLogs from devmem

"ACPI sysfs support for CCEL records" [1] is merged in linux kernel
since v6.4, and some old kernels may not have the sysfs feature.

Parse the CCEL EventLogs' physics address and length from the raw ACPI
table and read the EventLog from /dev/mem to faclitate old kernels.

Signed-off-by: GuoRui.Yu <[email protected]>
[1] torvalds/linux@4f855dc

* Make tdx_{eventlogs,extend_rtmr,tdreport,verify_rtmr} executable

Signed-off-by: GuoRui.Yu <[email protected]>

---------

Signed-off-by: GuoRui.Yu <[email protected]>
Co-authored-by: GuoRui.Yu <[email protected]>

Author: yuguorui

utilities/tdx/pytdxmeasure/pytdxmeasure/actor.py

@@ -4,6 +4,7 @@
 
 import os
 import logging
+import struct
 from typing import Dict, List
 from hashlib import sha384
 
@@ -89,8 +90,7 @@ def __init__(self, base, length):
         self._event_logs = []
         self._rtmrs = {}
 
-    def _read(self, ccel_file="/sys/firmware/acpi/tables/data/CCEL"):
-        assert os.path.exists(ccel_file), f"Could not find the CCEL file {ccel_file}"
+    def _read_direct(self, ccel_file):
         try:
             with open(ccel_file, "rb") as fobj:
                 self._data = fobj.read()
@@ -100,6 +100,62 @@ def _read(self, ccel_file="/sys/firmware/acpi/tables/data/CCEL"):
             LOG.error("Need root permission to open file %s", ccel_file)
             return None
 
+    def _read_from_devmem(self, acpi_file):
+        try:
+            with open(acpi_file, "rb") as fobj:
+                acpi_data = fobj.read()
+                assert len(acpi_data) > 0
+
+            # typedef struct {
+            #   UINT32  Signature;
+            #   UINT32  Length;
+            #   UINT8   Revision;
+            #   UINT8   Checksum;
+            #   UINT8   OemId[6];
+            #   UINT64  OemTableId;
+            #   UINT32  OemRevision;
+            #   UINT32  CreatorId;
+            #   UINT32  CreatorRevision;
+            # } EFI_ACPI_DESCRIPTION_HEADER;
+
+            # typedef struct {
+            #     EFI_ACPI_DESCRIPTION_HEADER Header;
+            #     UINT32                      Rsv;  // default to 0
+            #     UINT64                      Laml; // Optional
+            #     UINT64                      Lasa;
+            # } TDX_Event_Log_ACPI_Table;
+
+            # Read the CCEL table from the /sys/firmware/acpi/tables/CCEL
+            struct_fmt = "<4sI2B6sQ4IQQ"
+            ccel_acpi_table = struct.unpack(struct_fmt, acpi_data[:struct.calcsize(struct_fmt)])
+            (
+                signature, length, revision, checksum, oem_id, oem_table_id, oem_revision,
+                creator_id, creator_revision,
+                rsv, laml, lasa
+            ) = ccel_acpi_table
+
+            assert signature == b'CCEL', "Invalid CCEL ACPI table"
+            assert length == len(acpi_data), "Invalid CCEL ACPI table"
+            assert rsv == 0, "Invalid CCEL ACPI table"
+
+            with open("/dev/mem", "rb") as fobj:
+                fobj.seek(lasa)
+                self._data = fobj.read(laml)
+                assert len(self._data) > 0
+                return self._data
+
+        except (PermissionError, OSError):
+            LOG.error("Need root permission to open file %s", acpi_file)
+            return None
+
+    def _read(self, ccel_file="/sys/firmware/acpi/tables/data/CCEL", acpi_file="/sys/firmware/acpi/tables/CCEL"):
+        assert os.path.exists(ccel_file) or os.path.exists(acpi_file), f"Could not find the CCEL file and CCEL ACPI table"
+
+        if os.path.exists(ccel_file):
+            return self._read_direct(ccel_file)
+        else:
+            return self._read_from_devmem(acpi_file)
+
     @staticmethod
     def _replay_single_rtmr(event_logs: List[TDEventLogEntry]) -> RTMR:
         rtmr = bytearray(RTMR.RTMR_LENGTH_BY_BYTES)