Re: [PATCH 4/5] OvmfPkg/AcpiPlatformDxe: implement the QEMU_LOADER_WRITE_POINTER command

[Jordan Justen <jordan.l.justen@intel.com>]

On 2017-02-16 12:41:36, Laszlo Ersek wrote:
> 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>
> ---
>  OvmfPkg/AcpiPlatformDxe/QemuFwCfgAcpi.c | 171 +++++++++++++++++++-
>  1 file changed, 168 insertions(+), 3 deletions(-)
> 
> diff --git a/OvmfPkg/AcpiPlatformDxe/QemuFwCfgAcpi.c b/OvmfPkg/AcpiPlatformDxe/QemuFwCfgAcpi.c
> index 404589cad0b7..de827c2df204 100644
> --- a/OvmfPkg/AcpiPlatformDxe/QemuFwCfgAcpi.c
> +++ b/OvmfPkg/AcpiPlatformDxe/QemuFwCfgAcpi.c
> @@ -350,10 +350,147 @@ ProcessCmdAddChecksum (
>      AddChecksum->ResultOffset, AddChecksum->Start, AddChecksum->Length));
>    return EFI_SUCCESS;
>  }
>  
>  
> +/**
> +  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) {

What do you think of this instead?

  if (WritePointer->PointerSize < 8 &&
      RShiftU64 (PointerValue, WritePointer->PointerSize * 8) != 0) {

Patches 1-4 Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

> +    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).
>  //
>  #define INSTALLED_TABLES_MAX 128
> @@ -559,10 +696,11 @@ InstallQemuFwCfgTables (
>    EFI_STATUS               Status;
>    FIRMWARE_CONFIG_ITEM     FwCfgItem;
>    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;
>    UINTN                    *InstalledKey;
>    INT32                    Installed;
> @@ -595,10 +733,15 @@ 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:
>        Status = ProcessCmdAllocate (&LoaderEntry->Command.Allocate, Tracker);
>        break;
> @@ -611,25 +754,33 @@ InstallQemuFwCfgTables (
>      case QemuLoaderCmdAddChecksum:
>        Status = ProcessCmdAddChecksum (&LoaderEntry->Command.AddChecksum,
>                   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));
>        break;
>      }
>  
>      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;
>    }
>  
>    //
>    // second pass: identify and install ACPI tables
>    //
> @@ -656,11 +807,25 @@ InstallQemuFwCfgTables (
>      DEBUG ((EFI_D_INFO, "%a: installed %d tables\n", __FUNCTION__, Installed));
>    }
>  
>    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
>    // not directly part of some ACPI table.
>    //
> -- 
> 2.9.3
> 
>