Re: [PATCH v1 1/6] ShellPkg: acpiview: DBG2: Prevent buffer overruns

["Krzysztof Koch" <krzysztof.koch@arm.com>]

Hi Zhichao,

The reason why processing of the Debug Device Information Structure is split into:
1. loading the header
2. dumping the entire structure

Is because we want to let the users control how much of the structure is dumped. This is important for backward compatibility of the acpiview tool with the ACPI specification (and other specs).

New ACPI table fields are appended at the end of structures/tables. If, for example, we are asked to parse an old version of Debug Device Information Structure, the 'Length' field will tell us to ignore some of the newly added fields. These fields do not make sense in the context of an old version of the corresponding spec.

The following code in Dbg2Parser.c:

    // Make sure the Debug Device Information structure lies inside the table.
    if ((Offset + *DbgDevInfoLen) > AcpiTableLength) {
      IncrementErrorCount ();
      Print (
        L"ERROR: Invalid Debug Device Information structure length. " \
          L"DbgDevInfoLen = %d. RemainingTableBufferLength = %d. " \
          L"DBG2 parsing aborted.\n",
        *DbgDevInfoLen,
        AcpiTableLength - Offset
        );
      return;
    }

Makes sure that the user-provided structure length won't result in a buffer overrun with respect to the DBG2 table buffer. This way we allow users to specify how much of the structure they want to parse while still preventing buffer overruns.

In short, I'm not sure if getting rid of DbgDevInfoHeaderParser would work as you assume that the remaining table buffer length should be passed to ParseAcpi() as an argument, not the length of the Debug Device Information Structure. What do you think?

Kind regards,

Krzysztof

-----Original Message-----
From: Gao, Zhichao <zhichao.gao@intel.com> 
Sent: Monday, August 5, 2019 7:48
To: Krzysztof Koch <Krzysztof.Koch@arm.com>; devel@edk2.groups.io
Cc: Carsey, Jaben <jaben.carsey@intel.com>; Ni, Ray <ray.ni@intel.com>; Sami Mujawar <Sami.Mujawar@arm.com>; Matteo Carlini <Matteo.Carlini@arm.com>; nd <nd@arm.com>
Subject: RE: [PATCH v1 1/6] ShellPkg: acpiview: DBG2: Prevent buffer overruns

About DbgDevInfoHeaderParser and DbgDevInfoParser.
This patch would parse same DbgDevInfo twice, one for getting length, the other for dumping structure info.
How about the following?
Add one parameter for DumpDbgDeviceInfo

STATIC
VOID
EFIAPI
DumpDbgDeviceInfo (
  IN  UINT8*  Ptr,
  OUT UINT32* Length
  )

==>

STATIC
VOID
EFIAPI
DumpDbgDeviceInfo (
  IN  UINT8*  Ptr,
  IN  UINT32* Length			// remain length of acpi struct to parse to make sure all operation is in a valid scope
  OUT UINT16* DbgDevInfoLength	// return pointer dbgdevinfo length
  )

Then we would not need an anditional DbgDevInfoHeaderParser and the header would be parsed for only once.

Any better comments, please let me know.

Thanks,
Zhichao

> -----Original Message-----
> From: Krzysztof Koch [mailto:krzysztof.koch@arm.com]
> Sent: Thursday, August 1, 2019 4:44 PM
> To: devel@edk2.groups.io
> Cc: Carsey, Jaben <jaben.carsey@intel.com>; Ni, Ray 
> <ray.ni@intel.com>; Gao, Zhichao <zhichao.gao@intel.com>; 
> Sami.Mujawar@arm.com; Matteo.Carlini@arm.com; nd@arm.com
> Subject: [PATCH v1 1/6] ShellPkg: acpiview: DBG2: Prevent buffer 
> overruns
> 
> Modify the DBG2 table parsing logic to prevent reading past the ACPI 
> buffer lengths provided.
> 
> Modify the signature of the DumpDbgDeviceInfo() function to make it 
> consistent with the ACPI structure processing functions in other 
> acpiview parsers. Now, the length of the Debug Device Information 
> Structure is read before the entire structure is dumped.
> 
> This refactoring change makes it easier to stop reading beyond the
> DBG2 table buffer if the Debug Device Information Structure Buffer 
> does not fit in the DBG2 buffer.
> 
> For processing the first two fields of the Debug Device Information 
> Structure (to get the length) a new ACPI_PARSER array is defined.
> 
> References:
> - Microsoft Debug Port Table 2 (DBG2), December 10, 2015
> 
> Signed-off-by: Krzysztof Koch <krzysztof.koch@arm.com>
> ---
> 
> Notes:
>     v1:
>     - Prevent buffer overruns in DBG2 acpiview parser [Krzysztof]
> 
> 
> ShellPkg/Library/UefiShellAcpiViewCommandLib/Parsers/Dbg2/Dbg2Parser.c
> | 141 +++++++++++++-------
>  1 file changed, 92 insertions(+), 49 deletions(-)
> 
> diff --git
> a/ShellPkg/Library/UefiShellAcpiViewCommandLib/Parsers/Dbg2/Dbg2Parse
> r.c
> b/ShellPkg/Library/UefiShellAcpiViewCommandLib/Parsers/Dbg2/Dbg2Parse
> r.c
> index
> c6929695a1032c57761ef85002d6c51b7800ce23..869e700b9beda4886bf7bc5ae
> 4ced3ab9a59efa3 100644
> ---
> a/ShellPkg/Library/UefiShellAcpiViewCommandLib/Parsers/Dbg2/Dbg2Parse
> r.c
> +++
> b/ShellPkg/Library/UefiShellAcpiViewCommandLib/Parsers/Dbg2/Dbg2Pars
> +++ er.c
> @@ -64,10 +64,17 @@ STATIC CONST ACPI_PARSER Dbg2Parser[] = {
>     (VOID**)&NumberDbgDeviceInfo, NULL, NULL}  };
> 
> +/// An ACPI_PARSER array describing the debug device information 
> +structure /// header.
> +STATIC CONST ACPI_PARSER DbgDevInfoHeaderParser[] = {
> +  {L"Revision", 1, 0, L"0x%x", NULL, NULL, NULL, NULL},
> +  {L"Length", 2, 1, L"%d", NULL, (VOID**)&DbgDevInfoLen, NULL, NULL} 
> +};
> +
>  /// An ACPI_PARSER array describing the debug device information.
>  STATIC CONST ACPI_PARSER DbgDevInfoParser[] = {
>    {L"Revision", 1, 0, L"0x%x", NULL, NULL, NULL, NULL},
> -  {L"Length", 2, 1, L"%d", NULL, (VOID**)&DbgDevInfoLen, NULL, NULL},
> +  {L"Length", 2, 1, L"%d", NULL, NULL, NULL, NULL},
> 
>    {L"Generic Address Registers Count", 1, 3, L"0x%x", NULL,
>     (VOID**)&GasCount, NULL, NULL},
> @@ -93,76 +100,91 @@ STATIC CONST ACPI_PARSER DbgDevInfoParser[] = {
>  /**
>    This function parses the debug device information structure.
> 
> -  @param [in]  Ptr     Pointer to the start of the buffer.
> -  @param [out] Length  Pointer in which the length of the debug
> -                       device information is returned.
> +  @param [in] Ptr     Pointer to the start of the buffer.
> +  @param [in] Length  Length of the debug device information structure.
>  **/
>  STATIC
>  VOID
>  EFIAPI
>  DumpDbgDeviceInfo (
> -  IN  UINT8*  Ptr,
> -  OUT UINT32* Length
> +  IN UINT8* Ptr,
> +  IN UINT16 Length
>    )
>  {
>    UINT16  Index;
> -  UINT8*  DataPtr;
> -  UINT32* AddrSize;
> -
> -  // Parse the debug device info to get the Length
> -  ParseAcpi (
> -    FALSE,
> -    0,
> -    "Debug Device Info",
> -    Ptr,
> -    3,  // Length is 2 bytes starting at offset 1
> -    PARSER_PARAMS (DbgDevInfoParser)
> -    );
> +  UINT16  Offset;
> 
>    ParseAcpi (
>      TRUE,
>      2,
>      "Debug Device Info",
>      Ptr,
> -    *DbgDevInfoLen,
> +    Length,
>      PARSER_PARAMS (DbgDevInfoParser)
>      );
> 
> -  // GAS and Address Size
> +  // GAS
>    Index = 0;
> -  DataPtr = Ptr + (*BaseAddrRegOffset);
> -  AddrSize = (UINT32*)(Ptr + (*AddrSizeOffset));
> -  while (Index < (*GasCount)) {
> +  Offset = *BaseAddrRegOffset;
> +  while ((Index++ < *GasCount) &&
> +         (Offset < Length)) {
>      PrintFieldName (4, L"BaseAddressRegister");
> -    DumpGasStruct (DataPtr, 4, GAS_LENGTH);
> +    Offset += (UINT16)DumpGasStruct (
> +                        Ptr + Offset,
> +                        4,
> +                        Length - Offset
> +                        );
> +  }
> +
> +  // Make sure the array of address sizes corresponding to each GAS 
> + fit in the  // Debug Device Information structure  if 
> + ((*AddrSizeOffset + (*GasCount * sizeof (UINT32))) > Length) {
> +    IncrementErrorCount ();
> +    Print (
> +      L"ERROR: Invalid GAS count. GasCount = %d. 
> + RemainingBufferLength
> = %d. " \
> +        L"Parsing of the Debug Device Information structure aborted.\n",
> +      *GasCount,
> +      Length - *AddrSizeOffset
> +      );
> +    return;
> +  }
> +
> +  // Address Size
> +  Index = 0;
> +  Offset = *AddrSizeOffset;
> +  while ((Index++ < *GasCount) &&
> +         (Offset < Length)) {
>      PrintFieldName (4, L"Address Size");
> -    Print (L"0x%x\n", AddrSize[Index]);
> -    DataPtr += GAS_LENGTH;
> -    Index++;
> +    Print (L"0x%x\n", *((UINT32*)(Ptr + Offset)));
> +    Offset += sizeof (UINT32);
>    }
> 
>    // NameSpace String
>    Index = 0;
> -  DataPtr = Ptr + (*NameSpaceStringOffset);
> +  Offset = *NameSpaceStringOffset;
>    PrintFieldName (4, L"NameSpace String");
> -  while (Index < (*NameSpaceStringLength)) {
> -    Print (L"%c", DataPtr[Index++]);
> +  while ((Index++ < *NameSpaceStringLength) &&
> +         (Offset < Length)) {
> +    Print (L"%c", *(Ptr + Offset));
> +    Offset++;
>    }
>    Print (L"\n");
> 
>    // OEM Data
> -  Index = 0;
> -  DataPtr = Ptr + (*OEMDataOffset);
> -  PrintFieldName (4, L"OEM Data");
> -  while (Index < (*OEMDataLength)) {
> -    Print (L"%x ", DataPtr[Index++]);
> -    if ((Index & 7) == 0) {
> -      Print (L"\n%-*s   ", OUTPUT_FIELD_COLUMN_WIDTH, L"");
> +  if (*OEMDataOffset != 0) {
> +    Index = 0;
> +    Offset = *OEMDataOffset;
> +    PrintFieldName (4, L"OEM Data");
> +    while ((Index++ < *OEMDataLength) &&
> +           (Offset < Length)) {
> +      Print (L"%x ", *(Ptr + Offset));
> +      if ((Index & 7) == 0) {
> +        Print (L"\n%-*s   ", OUTPUT_FIELD_COLUMN_WIDTH, L"");
> +      }
> +      Offset++;
>      }
> +    Print (L"\n");
>    }
> -  Print (L"\n");
> -
> -  *Length = *DbgDevInfoLen;
>  }
> 
>  /**
> @@ -187,8 +209,7 @@ ParseAcpiDbg2 (
>    )
>  {
>    UINT32 Offset;
> -  UINT32 DbgDeviceInfoLength;
> -  UINT8* DevInfoPtr;
> +  UINT32 Index;
> 
>    if (!Trace) {
>      return;
> @@ -202,14 +223,36 @@ ParseAcpiDbg2 (
>               AcpiTableLength,
>               PARSER_PARAMS (Dbg2Parser)
>               );
> -  DevInfoPtr = Ptr + Offset;
> 
> -  while (Offset < AcpiTableLength) {
> -    DumpDbgDeviceInfo (
> -      DevInfoPtr,
> -      &DbgDeviceInfoLength
> +  Offset = *OffsetDbgDeviceInfo;
> +  Index = 0;
> +
> +  while (Index++ < *NumberDbgDeviceInfo) {
> +
> +    // Parse the Debug Device Information Structure header to obtain Length
> +    ParseAcpi (
> +      FALSE,
> +      0,
> +      NULL,
> +      Ptr + Offset,
> +      AcpiTableLength - Offset,
> +      PARSER_PARAMS (DbgDevInfoHeaderParser)
>        );
> -    Offset += DbgDeviceInfoLength;
> -    DevInfoPtr += DbgDeviceInfoLength;
> +
> +    // Make sure the Debug Device Information structure lies inside the table.
> +    if ((Offset + *DbgDevInfoLen) > AcpiTableLength) {
> +      IncrementErrorCount ();
> +      Print (
> +        L"ERROR: Invalid Debug Device Information structure length. " \
> +          L"DbgDevInfoLen = %d. RemainingTableBufferLength = %d. " \
> +          L"DBG2 parsing aborted.\n",
> +        *DbgDevInfoLen,
> +        AcpiTableLength - Offset
> +        );
> +      return;
> +    }
> +
> +    DumpDbgDeviceInfo (Ptr + Offset, (*DbgDevInfoLen));
> +    Offset += (*DbgDevInfoLen);
>    }
>  }
> --
> 'Guid(CE165669-3EF3-493F-B85D-6190EE5B9759)'
>