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>

1 files changed, 168 insertions, 3 deletions

diff --git a/OvmfPkg/AcpiPlatformDxe/QemuFwCfgAcpi.c b/OvmfPkg/AcpiPlatformDxe/QemuFwCfgAcpi.c
index 404589cad0..de827c2df2 100644
--- a/OvmfPkg/AcpiPlatformDxe/QemuFwCfgAcpi.c
+++ b/OvmfPkg/AcpiPlatformDxe/QemuFwCfgAcpi.c
@@ -352,6 +352,143 @@ ProcessCmdAddChecksum (
 }

 

 

+/**

+  Process a QEMU_LOADER_WRITE_POINTER command.

+

+  @param[in] WritePointer   The QEMU_LOADER_WRITE_POINTER command to process.

+

+  @param[in] Tracker        The ORDERED_COLLECTION tracking the BLOB user

+                            structures created thus far.

+

+  @retval EFI_PROTOCOL_ERROR  Malformed fw_cfg file name(s) have been found in

+                              WritePointer. Or, the WritePointer command

+                              references a file unknown to Tracker or the

+                              fw_cfg directory. Or, the pointer object to

+                              rewrite has invalid location, size, or initial

+                              relative value. Or, the pointer value to store

+                              does not fit in the given pointer size.

+

+  @retval EFI_SUCCESS         The pointer object inside the writeable fw_cfg

+                              file has been written.

+**/

+STATIC

+EFI_STATUS

+ProcessCmdWritePointer (

+  IN     CONST QEMU_LOADER_WRITE_POINTER *WritePointer,

+  IN     CONST ORDERED_COLLECTION        *Tracker

+  )

+{

+  RETURN_STATUS            Status;

+  FIRMWARE_CONFIG_ITEM     PointerItem;

+  UINTN                    PointerItemSize;

+  ORDERED_COLLECTION_ENTRY *PointeeEntry;

+  BLOB                     *PointeeBlob;

+  UINT64                   PointerValue;

+

+  if (WritePointer->PointerFile[QEMU_LOADER_FNAME_SIZE - 1] != '\0' ||

+      WritePointer->PointeeFile[QEMU_LOADER_FNAME_SIZE - 1] != '\0') {

+    DEBUG ((DEBUG_ERROR, "%a: malformed file name\n", __FUNCTION__));

+    return EFI_PROTOCOL_ERROR;

+  }

+

+  Status = QemuFwCfgFindFile ((CONST CHAR8 *)WritePointer->PointerFile,

+             &PointerItem, &PointerItemSize);

+  PointeeEntry = OrderedCollectionFind (Tracker, WritePointer->PointeeFile);

+  if (RETURN_ERROR (Status) || PointeeEntry == NULL) {

+    DEBUG ((DEBUG_ERROR,

+      "%a: invalid fw_cfg file or blob reference \"%a\" / \"%a\"\n",

+      __FUNCTION__, WritePointer->PointerFile, WritePointer->PointeeFile));

+    return EFI_PROTOCOL_ERROR;

+  }

+

+  if ((WritePointer->PointerSize != 1 && WritePointer->PointerSize != 2 &&

+       WritePointer->PointerSize != 4 && WritePointer->PointerSize != 8) ||

+      (PointerItemSize < WritePointer->PointerSize) ||

+      (PointerItemSize - WritePointer->PointerSize <

+       WritePointer->PointerOffset)) {

+    DEBUG ((DEBUG_ERROR, "%a: invalid pointer location or size in \"%a\"\n",

+      __FUNCTION__, WritePointer->PointerFile));

+    return EFI_PROTOCOL_ERROR;

+  }

+

+  PointeeBlob = OrderedCollectionUserStruct (PointeeEntry);

+  PointerValue = WritePointer->PointeeOffset;

+  if (PointerValue >= PointeeBlob->Size) {

+    DEBUG ((DEBUG_ERROR, "%a: invalid PointeeOffset\n", __FUNCTION__));

+    return EFI_PROTOCOL_ERROR;

+  }

+

+  //

+  // The memory allocation system ensures that the address of the byte past the

+  // last byte of any allocated object is expressible (no wraparound).

+  //

+  ASSERT ((UINTN)PointeeBlob->Base <= MAX_ADDRESS - PointeeBlob->Size);

+

+  PointerValue += (UINT64)(UINTN)PointeeBlob->Base;

+  if (RShiftU64 (

+        RShiftU64 (PointerValue, WritePointer->PointerSize * 8 - 1), 1) != 0) {

+    DEBUG ((DEBUG_ERROR, "%a: pointer value unrepresentable in \"%a\"\n",

+      __FUNCTION__, WritePointer->PointerFile));

+    return EFI_PROTOCOL_ERROR;

+  }

+

+  QemuFwCfgSelectItem (PointerItem);

+  QemuFwCfgSkipBytes (WritePointer->PointerOffset);

+  QemuFwCfgWriteBytes (WritePointer->PointerSize, &PointerValue);

+

+  //

+  // Because QEMU has now learned PointeeBlob->Base, we must mark PointeeBlob

+  // as unreleasable, for the case when the whole linker/loader script is

+  // handled successfully.

+  //

+  PointeeBlob->HostsOnlyTableData = FALSE;

+

+  DEBUG ((DEBUG_VERBOSE, "%a: PointerFile=\"%a\" PointeeFile=\"%a\" "

+    "PointerOffset=0x%x PointeeOffset=0x%x PointerSize=%d\n", __FUNCTION__,

+    WritePointer->PointerFile, WritePointer->PointeeFile,

+    WritePointer->PointerOffset, WritePointer->PointeeOffset,

+    WritePointer->PointerSize));

+  return EFI_SUCCESS;

+}

+

+

+/**

+  Undo a QEMU_LOADER_WRITE_POINTER command.

+

+  This function revokes (zeroes out) a guest memory reference communicated to

+  QEMU earlier. The caller is responsible for invoking this function only on

+  such QEMU_LOADER_WRITE_POINTER commands that have been successfully processed

+  by ProcessCmdWritePointer().

+

+  @param[in] WritePointer  The QEMU_LOADER_WRITE_POINTER command to undo.

+**/

+STATIC

+VOID

+UndoCmdWritePointer (

+  IN CONST QEMU_LOADER_WRITE_POINTER *WritePointer

+  )

+{

+  RETURN_STATUS        Status;

+  FIRMWARE_CONFIG_ITEM PointerItem;

+  UINTN                PointerItemSize;

+  UINT64               PointerValue;

+

+  Status = QemuFwCfgFindFile ((CONST CHAR8 *)WritePointer->PointerFile,

+             &PointerItem, &PointerItemSize);

+  ASSERT_RETURN_ERROR (Status);

+

+  PointerValue = 0;

+  QemuFwCfgSelectItem (PointerItem);

+  QemuFwCfgSkipBytes (WritePointer->PointerOffset);

+  QemuFwCfgWriteBytes (WritePointer->PointerSize, &PointerValue);

+

+  DEBUG ((DEBUG_VERBOSE,

+    "%a: PointerFile=\"%a\" PointerOffset=0x%x PointerSize=%d\n", __FUNCTION__,

+    WritePointer->PointerFile, WritePointer->PointerOffset,

+    WritePointer->PointerSize));

+}

+

+

 //

 // We'll be saving the keys of installed tables so that we can roll them back

 // in case of failure. 128 tables should be enough for anyone (TM).

@@ -561,6 +698,7 @@ InstallQemuFwCfgTables (
   UINTN                    FwCfgSize;

   QEMU_LOADER_ENTRY        *LoaderStart;

   CONST QEMU_LOADER_ENTRY  *LoaderEntry, *LoaderEnd;

+  CONST QEMU_LOADER_ENTRY  *WritePointerSubsetEnd;

   ORIGINAL_ATTRIBUTES      *OriginalPciAttributes;

   UINTN                    OriginalPciAttributesCount;

   ORDERED_COLLECTION       *Tracker;

@@ -597,6 +735,11 @@ InstallQemuFwCfgTables (
   //

   // first pass: process the commands

   //

+  // "WritePointerSubsetEnd" points one past the last successful

+  // QEMU_LOADER_WRITE_POINTER command. Now when we're about to start the first

+  // pass, no such command has been encountered yet.

+  //

+  WritePointerSubsetEnd = LoaderStart;

   for (LoaderEntry = LoaderStart; LoaderEntry < LoaderEnd; ++LoaderEntry) {

     switch (LoaderEntry->Type) {

     case QemuLoaderCmdAllocate:

@@ -613,6 +756,14 @@ InstallQemuFwCfgTables (
                  Tracker);

       break;

 

+    case QemuLoaderCmdWritePointer:

+        Status = ProcessCmdWritePointer (&LoaderEntry->Command.WritePointer,

+                   Tracker);

+        if (!EFI_ERROR (Status)) {

+          WritePointerSubsetEnd = LoaderEntry + 1;

+        }

+        break;

+

     default:

       DEBUG ((EFI_D_VERBOSE, "%a: unknown loader command: 0x%x\n",

         __FUNCTION__, LoaderEntry->Type));

@@ -620,14 +771,14 @@ InstallQemuFwCfgTables (
     }

 

     if (EFI_ERROR (Status)) {

-      goto FreeTracker;

+      goto RollbackWritePointersAndFreeTracker;

     }

   }

 

   InstalledKey = AllocatePool (INSTALLED_TABLES_MAX * sizeof *InstalledKey);

   if (InstalledKey == NULL) {

     Status = EFI_OUT_OF_RESOURCES;

-    goto FreeTracker;

+    goto RollbackWritePointersAndFreeTracker;

   }

 

   //

@@ -658,7 +809,21 @@ InstallQemuFwCfgTables (
 

   FreePool (InstalledKey);

 

-FreeTracker:

+RollbackWritePointersAndFreeTracker:

+  //

+  // In case of failure, revoke any allocation addresses that were communicated

+  // to QEMU previously, before we release all the blobs.

+  //

+  if (EFI_ERROR (Status)) {

+    LoaderEntry = WritePointerSubsetEnd;

+    while (LoaderEntry > LoaderStart) {

+      --LoaderEntry;

+      if (LoaderEntry->Type == QemuLoaderCmdWritePointer) {

+        UndoCmdWritePointer (&LoaderEntry->Command.WritePointer);

+      }

+    }

+  }

+

   //

   // Tear down the tracker infrastructure. Each fw_cfg blob will be left in

   // place only if we're exiting with success and the blob hosts data that is