OvmfPkg/AcpiPlatformDxe: implement the QEMU_LOADER_WRITE_POINTER command

The QEMU_LOADER_WRITE_POINTER command instructs the firmware to write the
address of a field within a previously allocated/downloaded fw_cfg blob
into another (writeable) fw_cfg file at a specific offset.

Put differently, QEMU_LOADER_WRITE_POINTER propagates, to QEMU, the
address that QEMU_LOADER_ALLOCATE placed the designated fw_cfg blob at, as
adjusted for the given field inside the allocated blob.

The implementation is similar to that of QEMU_LOADER_ADD_POINTER. Since
here we "patch" a pointer object in "fw_cfg file space", not guest memory
space, we utilize the QemuFwCfgSkipBytes() and QemuFwCfgWriteBytes() APIs
completed in commit range 465663e9f128..7fcb73541299.

An interesting aspect is that QEMU_LOADER_WRITE_POINTER creates a
host-level reference to a guest memory location. Therefore, if we fail to
process the linker/loader script for any reason, we have to clear out
those references first, before we release the guest memory allocations in
response to the error.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=359
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

diff --git a/OvmfPkg/AcpiPlatformDxe/QemuFwCfgAcpi.c b/OvmfPkg/AcpiPlatformDxe/QemuFwCfgAcpi.c
index 404589cad0b7952b2b9a9e7bc62a7641ea943f1f..de827c2df2040b623c0084b353fdf60614a69c86 100644 (file)
--- a/OvmfPkg/AcpiPlatformDxe/QemuFwCfgAcpi.c
+++ b/OvmfPkg/AcpiPlatformDxe/QemuFwCfgAcpi.c
@@ -352,6 +352,143 @@ ProcessCmdAddChecksum (
 }\r
 \r
 \r
+/**\r
+  Process a QEMU_LOADER_WRITE_POINTER command.\r
+\r
+  @param[in] WritePointer   The QEMU_LOADER_WRITE_POINTER command to process.\r
+\r
+  @param[in] Tracker        The ORDERED_COLLECTION tracking the BLOB user\r
+                            structures created thus far.\r
+\r
+  @retval EFI_PROTOCOL_ERROR  Malformed fw_cfg file name(s) have been found in\r
+                              WritePointer. Or, the WritePointer command\r
+                              references a file unknown to Tracker or the\r
+                              fw_cfg directory. Or, the pointer object to\r
+                              rewrite has invalid location, size, or initial\r
+                              relative value. Or, the pointer value to store\r
+                              does not fit in the given pointer size.\r
+\r
+  @retval EFI_SUCCESS         The pointer object inside the writeable fw_cfg\r
+                              file has been written.\r
+**/\r
+STATIC\r
+EFI_STATUS\r
+ProcessCmdWritePointer (\r
+  IN     CONST QEMU_LOADER_WRITE_POINTER *WritePointer,\r
+  IN     CONST ORDERED_COLLECTION        *Tracker\r
+  )\r
+{\r
+  RETURN_STATUS            Status;\r
+  FIRMWARE_CONFIG_ITEM     PointerItem;\r
+  UINTN                    PointerItemSize;\r
+  ORDERED_COLLECTION_ENTRY *PointeeEntry;\r
+  BLOB                     *PointeeBlob;\r
+  UINT64                   PointerValue;\r
+\r
+  if (WritePointer->PointerFile[QEMU_LOADER_FNAME_SIZE - 1] != '\0' ||\r
+      WritePointer->PointeeFile[QEMU_LOADER_FNAME_SIZE - 1] != '\0') {\r
+    DEBUG ((DEBUG_ERROR, "%a: malformed file name\n", __FUNCTION__));\r
+    return EFI_PROTOCOL_ERROR;\r
+  }\r
+\r
+  Status = QemuFwCfgFindFile ((CONST CHAR8 *)WritePointer->PointerFile,\r
+             &PointerItem, &PointerItemSize);\r
+  PointeeEntry = OrderedCollectionFind (Tracker, WritePointer->PointeeFile);\r
+  if (RETURN_ERROR (Status) || PointeeEntry == NULL) {\r
+    DEBUG ((DEBUG_ERROR,\r
+      "%a: invalid fw_cfg file or blob reference \"%a\" / \"%a\"\n",\r
+      __FUNCTION__, WritePointer->PointerFile, WritePointer->PointeeFile));\r
+    return EFI_PROTOCOL_ERROR;\r
+  }\r
+\r
+  if ((WritePointer->PointerSize != 1 && WritePointer->PointerSize != 2 &&\r
+       WritePointer->PointerSize != 4 && WritePointer->PointerSize != 8) ||\r
+      (PointerItemSize < WritePointer->PointerSize) ||\r
+      (PointerItemSize - WritePointer->PointerSize <\r
+       WritePointer->PointerOffset)) {\r
+    DEBUG ((DEBUG_ERROR, "%a: invalid pointer location or size in \"%a\"\n",\r
+      __FUNCTION__, WritePointer->PointerFile));\r
+    return EFI_PROTOCOL_ERROR;\r
+  }\r
+\r
+  PointeeBlob = OrderedCollectionUserStruct (PointeeEntry);\r
+  PointerValue = WritePointer->PointeeOffset;\r
+  if (PointerValue >= PointeeBlob->Size) {\r
+    DEBUG ((DEBUG_ERROR, "%a: invalid PointeeOffset\n", __FUNCTION__));\r
+    return EFI_PROTOCOL_ERROR;\r
+  }\r
+\r
+  //\r
+  // The memory allocation system ensures that the address of the byte past the\r
+  // last byte of any allocated object is expressible (no wraparound).\r
+  //\r
+  ASSERT ((UINTN)PointeeBlob->Base <= MAX_ADDRESS - PointeeBlob->Size);\r
+\r
+  PointerValue += (UINT64)(UINTN)PointeeBlob->Base;\r
+  if (RShiftU64 (\r
+        RShiftU64 (PointerValue, WritePointer->PointerSize * 8 - 1), 1) != 0) {\r
+    DEBUG ((DEBUG_ERROR, "%a: pointer value unrepresentable in \"%a\"\n",\r
+      __FUNCTION__, WritePointer->PointerFile));\r
+    return EFI_PROTOCOL_ERROR;\r
+  }\r
+\r
+  QemuFwCfgSelectItem (PointerItem);\r
+  QemuFwCfgSkipBytes (WritePointer->PointerOffset);\r
+  QemuFwCfgWriteBytes (WritePointer->PointerSize, &PointerValue);\r
+\r
+  //\r
+  // Because QEMU has now learned PointeeBlob->Base, we must mark PointeeBlob\r
+  // as unreleasable, for the case when the whole linker/loader script is\r
+  // handled successfully.\r
+  //\r
+  PointeeBlob->HostsOnlyTableData = FALSE;\r
+\r
+  DEBUG ((DEBUG_VERBOSE, "%a: PointerFile=\"%a\" PointeeFile=\"%a\" "\r
+    "PointerOffset=0x%x PointeeOffset=0x%x PointerSize=%d\n", __FUNCTION__,\r
+    WritePointer->PointerFile, WritePointer->PointeeFile,\r
+    WritePointer->PointerOffset, WritePointer->PointeeOffset,\r
+    WritePointer->PointerSize));\r
+  return EFI_SUCCESS;\r
+}\r
+\r
+\r
+/**\r
+  Undo a QEMU_LOADER_WRITE_POINTER command.\r
+\r
+  This function revokes (zeroes out) a guest memory reference communicated to\r
+  QEMU earlier. The caller is responsible for invoking this function only on\r
+  such QEMU_LOADER_WRITE_POINTER commands that have been successfully processed\r
+  by ProcessCmdWritePointer().\r
+\r
+  @param[in] WritePointer  The QEMU_LOADER_WRITE_POINTER command to undo.\r
+**/\r
+STATIC\r
+VOID\r
+UndoCmdWritePointer (\r
+  IN CONST QEMU_LOADER_WRITE_POINTER *WritePointer\r
+  )\r
+{\r
+  RETURN_STATUS        Status;\r
+  FIRMWARE_CONFIG_ITEM PointerItem;\r
+  UINTN                PointerItemSize;\r
+  UINT64               PointerValue;\r
+\r
+  Status = QemuFwCfgFindFile ((CONST CHAR8 *)WritePointer->PointerFile,\r
+             &PointerItem, &PointerItemSize);\r
+  ASSERT_RETURN_ERROR (Status);\r
+\r
+  PointerValue = 0;\r
+  QemuFwCfgSelectItem (PointerItem);\r
+  QemuFwCfgSkipBytes (WritePointer->PointerOffset);\r
+  QemuFwCfgWriteBytes (WritePointer->PointerSize, &PointerValue);\r
+\r
+  DEBUG ((DEBUG_VERBOSE,\r
+    "%a: PointerFile=\"%a\" PointerOffset=0x%x PointerSize=%d\n", __FUNCTION__,\r
+    WritePointer->PointerFile, WritePointer->PointerOffset,\r
+    WritePointer->PointerSize));\r
+}\r
+\r
+\r
 //\r
 // We'll be saving the keys of installed tables so that we can roll them back\r
 // in case of failure. 128 tables should be enough for anyone (TM).\r
@@ -561,6 +698,7 @@ InstallQemuFwCfgTables (
   UINTN                    FwCfgSize;\r
   QEMU_LOADER_ENTRY        *LoaderStart;\r
   CONST QEMU_LOADER_ENTRY  *LoaderEntry, *LoaderEnd;\r
+  CONST QEMU_LOADER_ENTRY  *WritePointerSubsetEnd;\r
   ORIGINAL_ATTRIBUTES      *OriginalPciAttributes;\r
   UINTN                    OriginalPciAttributesCount;\r
   ORDERED_COLLECTION       *Tracker;\r
@@ -597,6 +735,11 @@ InstallQemuFwCfgTables (
   //\r
   // first pass: process the commands\r
   //\r
+  // "WritePointerSubsetEnd" points one past the last successful\r
+  // QEMU_LOADER_WRITE_POINTER command. Now when we're about to start the first\r
+  // pass, no such command has been encountered yet.\r
+  //\r
+  WritePointerSubsetEnd = LoaderStart;\r
   for (LoaderEntry = LoaderStart; LoaderEntry < LoaderEnd; ++LoaderEntry) {\r
     switch (LoaderEntry->Type) {\r
     case QemuLoaderCmdAllocate:\r
@@ -613,6 +756,14 @@ InstallQemuFwCfgTables (
                  Tracker);\r
       break;\r
 \r
+    case QemuLoaderCmdWritePointer:\r
+        Status = ProcessCmdWritePointer (&LoaderEntry->Command.WritePointer,\r
+                   Tracker);\r
+        if (!EFI_ERROR (Status)) {\r
+          WritePointerSubsetEnd = LoaderEntry + 1;\r
+        }\r
+        break;\r
+\r
     default:\r
       DEBUG ((EFI_D_VERBOSE, "%a: unknown loader command: 0x%x\n",\r
         __FUNCTION__, LoaderEntry->Type));\r
@@ -620,14 +771,14 @@ InstallQemuFwCfgTables (
     }\r
 \r
     if (EFI_ERROR (Status)) {\r
-      goto FreeTracker;\r
+      goto RollbackWritePointersAndFreeTracker;\r
     }\r
   }\r
 \r
   InstalledKey = AllocatePool (INSTALLED_TABLES_MAX * sizeof *InstalledKey);\r
   if (InstalledKey == NULL) {\r
     Status = EFI_OUT_OF_RESOURCES;\r
-    goto FreeTracker;\r
+    goto RollbackWritePointersAndFreeTracker;\r
   }\r
 \r
   //\r
@@ -658,7 +809,21 @@ InstallQemuFwCfgTables (
 \r
   FreePool (InstalledKey);\r
 \r
-FreeTracker:\r
+RollbackWritePointersAndFreeTracker:\r
+  //\r
+  // In case of failure, revoke any allocation addresses that were communicated\r
+  // to QEMU previously, before we release all the blobs.\r
+  //\r
+  if (EFI_ERROR (Status)) {\r
+    LoaderEntry = WritePointerSubsetEnd;\r
+    while (LoaderEntry > LoaderStart) {\r
+      --LoaderEntry;\r
+      if (LoaderEntry->Type == QemuLoaderCmdWritePointer) {\r
+        UndoCmdWritePointer (&LoaderEntry->Command.WritePointer);\r
+      }\r
+    }\r
+  }\r
+\r
   //\r
   // Tear down the tracker infrastructure. Each fw_cfg blob will be left in\r
   // place only if we're exiting with success and the blob hosts data that is\r