BRLY-2021-043

SMM arbitrary code execution in USBRT SMM driver on Dell devices.

Public Disclosure Date: Mar 10, 2022

CVE ID

CVE-2022-24420

Vendors Affected

AMI

Products Affected

DELL Inspiron 15 Gaming 7567

Summary

BINARLY efiXplorer team has discovered SMM arbitrary code execution on Dell devices.

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Potential Impact

An attacker can exploit this vulnerability to elevate privileges from ring 0 to ring -2, execute arbitrary code in System Management Mode - an environment more privileged than operating system (OS) and completely isolated from it. Running arbitrary code in SMM additionally bypasses SMM-based SPI flash protections against modifications, which can help an attacker to install a firmware backdoor/implant into BIOS. Such a malicious firmware code in BIOS could persist across operating system re-installs. Additionally, this vulnerability potentially could be used by malicious actors to bypass security mechanisms provided by UEFI firmware (for example, Secure Boot and some types of memory isolation for hypervisors).

Vulnerability Information

BINARLY internal vulnerability identifier: BRLY-2021-043
CERT/CC assigned case number: VU#540990
Dell PSIRT assigned CVE identifier: CVE-2022-24420
CVSS v3.1 8.2 High AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H

Table of Contents

01.Affected Intel firmware

02.Vulnerability description

03.Disclosure timeline

04.Acknowledgements

Affected Intel firmware

Device/Firmware	File Name	SHA256 (File PE32 section)	File GUID
DELL Inspiron 15 Gaming 7567	USBRT	05011cd7c3b27b2e723ed88f7c4d0512ed1045c5265897aefba73fd6b8e7fece	04EAAAA1-29A1-11D7-8838-00500473D4EB

Vulnerability description

The vulnerability exists in SW SMI handler located at offset 0x1BC8 in the driver. The handler is registered as follows:

result = (gSmst->SmmLocateProtocol)(&EFI_SMM_SW_DISPATCH2_PROTOCOL_GUID, 0, &EfiSmmSwDispatch2Protocol);
if ( result >= 0 )
{
  RegisterContext.SwSmiInputValue = 0x31;
  EfiSmmSwDispatch2Protocol->Register(EfiSmmSwDispatch2Protocol, SmiHandler, &RegisterContext, &DispatchHandle);
  ...
}

The pseudocode of the vulnerable handler is shown below:

EFI_STATUS __fastcall SmiHandler(
        EFI_HANDLE DispatchHandle,
        const void *Context,
        void *CommBuffer,
        UINTN *CommBufferSize)
{
  // [COLLAPSED LOCAL DECLARATIONS. PRESS KEYPAD CTRL-"+" TO EXPAND]

  UsbData = gUsbData;
  Struct = *(gUsbData + 25824);
  if ( Struct )
  {
    *(gUsbData + 25824) = 0;
  }
  else
  {
    if ( (*(gUsbData + 8) & 0x10) != 0 )
      return 0;
    Struct = *(16 * MEMORY[0x40E] + 260);
    // check that the buffer does not overlap with SMRAM
    if ( BufferValidation(Struct, 47) < EFI_SUCCESS )
      return 0;
    *(UsbData + 26904) = 1;
  }
  if ( !Struct )
    return 0;
  FuncIndex = *Struct;
  if ( !*Struct )
    goto _Exec;
  if ( FuncIndex >= 32 && FuncIndex <= 56 )
  {
    FuncIndex -= 31;
_Exec:
    (gUsbApiTable[FuncIndex])(Struct);
    UsbData = gUsbData;
  }
  if ( !*(UsbData + 25824) )
    *(UsbData + 26904) = 0;
  return 0;
}

Struct value can be controlled by attacker with Ring 0 privileges. If FuncIndex == 14, than the function located at offset 0x3080 will be called:

__int64 __fastcall UsbApiHcProc(STRUCT *Struc)
{
  // [COLLAPSED LOCAL DECLARATIONS. PRESS KEYPAD CTRL-"+" TO EXPAND]

  result = Invoke(
             *(192 * ((Struc->HcType - 16) >> 4) + gUsbData + 112 + 8 * Struc->SubfuncIndex + 8),
             Struc->ParamBuffer,
             (Struc->ParamSize + 3) & ~3u);
  Struc->RetVal = 0;
  Struc->ApiRetVal = result;
  return result;
}

The first argument to the Invoke function is a pointer to be retrieved from the structure pointed to by gUsbData. The pseudocode of the Invoke function is shown below:

__int64 __fastcall Invoke(__int64 (*Ptr)(void), _QWORD *ParamBuffer, unsigned int ParamSize)
{
  // [COLLAPSED LOCAL DECLARATIONS. PRESS KEYPAD CTRL-"+" TO EXPAND]

  v3 = ParamSize >> 3;
  if ( !v3 )
    return Ptr();
  v4 = v3 - 1;
  if ( !v4 )
    return (Ptr)(*ParamBuffer);
  v5 = v4 - 1;
  if ( !v5 )
    return (Ptr)(*ParamBuffer, ParamBuffer[1]);
  v6 = v5 - 1;
  if ( !v6 )
    return (Ptr)(*ParamBuffer, ParamBuffer[1], ParamBuffer[2]);
  v7 = v6 - 1;
  if ( !v7 )
    return (Ptr)(*ParamBuffer, ParamBuffer[1], ParamBuffer[2], ParamBuffer[3]);
  v8 = v7 - 1;
  if ( !v8 )
    return (Ptr)(*ParamBuffer, ParamBuffer[1], ParamBuffer[2], ParamBuffer[3], ParamBuffer[4]);
  v9 = v8 - 1;
  if ( !v9 )
    return (Ptr)(*ParamBuffer, ParamBuffer[1], ParamBuffer[2], ParamBuffer[3], ParamBuffer[4], ParamBuffer[5]);
  if ( v9 == 1 )
    return (Ptr)(
             *ParamBuffer,
             ParamBuffer[1],
             ParamBuffer[2],
             ParamBuffer[3],
             ParamBuffer[4],
             ParamBuffer[5],
             ParamBuffer[6]);
  return 0;
}

According to this pseudocode, if an attacker can control a pointer, then he can execute an arbitrary function and pass up to 7 parameters to it.

gUsbData structure initialized in UHCD DXE driver (GUID: 580DD900-385D-11D7-883A-00500473D4EB). The pseudocode of the function used for initialization shown below:

void *__cdecl AllocatePoolWithAlign(UINTN AllocationSize, UINTN Align)
{
  // [COLLAPSED LOCAL DECLARATIONS. PRESS KEYPAD CTRL-"+" TO EXPAND]

  Align_1 = Align;
  Size = AllocationSize;
  Memory = 0xFFFFFFFF;
  gFlag = 0;
  if ( (gBS_0->AllocatePages(AllocateMaxAddress, EfiRuntimeServicesData, 0x10, &Memory) & 0x8000000000000000) != 0
    && (gBS_0->AllocatePages(AllocateAnyPages, EfiRuntimeServicesData, 0x10, &Memory) & 0x8000000000000000) != 0 )
  {
    return 0;
  }
  gMem = Memory;
  gBS_0->SetMem(Memory, 0x10000, 0);
  qword_BF98 = 0;
  qword_BFA8 = 0xFFFF;
  v5 = 0 % Align_1;
  if ( v5 )
    v6 = Align_1 - v5;
  else
    v6 = 0;
  gMem = v6 + Size;
  return (v6 & -(v6 + Size < 0xFFFF));
}

This means that an attacker with Ring 0 privileges will be able to find this buffer in system memory and modify it to execute arbitrary code.

To fix this problem, you need to check the pointer passed to the Invoke function (for example, call a function from a global table after checking the index).

Disclosure timeline

This bug is subject to a 90 day disclosure deadline. After 90 days elapsed or a patch has been made broadly available (whichever is earlier), the bug report will become visible to the public.

Disclosure Activity	Date
Dell PSIRT is notified	2021-12-08
Dell PSIRT confirmed reported issue	2022-02-25
Dell PSIRT assigned CVE number	2022-02-25
Dell PSIRT provide patch release	2022-02-25
BINARLY public disclosure date	2022-03-10

Acknowledgements

BINARLY efiXplorer team

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Potential Impact

Device/Firmware

File Name

SHA256 (File PE32 section)

File GUID

DELL Inspiron 15 Gaming 7567

USBRT

05011cd7c3b27b2e723ed88f7c4d0512ed1045c5265897aefba73fd6b8e7fece

04EAAAA1-29A1-11D7-8838-00500473D4EB

result = (gSmst->SmmLocateProtocol)(&EFI_SMM_SW_DISPATCH2_PROTOCOL_GUID, 0, &EfiSmmSwDispatch2Protocol); if ( result >= 0 ) { RegisterContext.SwSmiInputValue = 0x31; EfiSmmSwDispatch2Protocol->Register(EfiSmmSwDispatch2Protocol, SmiHandler, &RegisterContext, &DispatchHandle); ... }

EFI_STATUS __fastcall SmiHandler( EFI_HANDLE DispatchHandle, const void *Context, void *CommBuffer, UINTN *CommBufferSize) { // [COLLAPSED LOCAL DECLARATIONS. PRESS KEYPAD CTRL-"+" TO EXPAND] UsbData = gUsbData; Struct = *(gUsbData + 25824); if ( Struct ) { *(gUsbData + 25824) = 0; } else { if ( (*(gUsbData + 8) & 0x10) != 0 ) return 0; Struct = *(16 * MEMORY[0x40E] + 260); // check that the buffer does not overlap with SMRAM if ( BufferValidation(Struct, 47) < EFI_SUCCESS ) return 0; *(UsbData + 26904) = 1; } if ( !Struct ) return 0; FuncIndex = *Struct; if ( !*Struct ) goto _Exec; if ( FuncIndex >= 32 && FuncIndex <= 56 ) { FuncIndex -= 31; _Exec: (gUsbApiTable[FuncIndex])(Struct); UsbData = gUsbData; } if ( !*(UsbData + 25824) ) *(UsbData + 26904) = 0; return 0; }

__int64 __fastcall UsbApiHcProc(STRUCT *Struc) { // [COLLAPSED LOCAL DECLARATIONS. PRESS KEYPAD CTRL-"+" TO EXPAND] result = Invoke( *(192 * ((Struc->HcType - 16) >> 4) + gUsbData + 112 + 8 * Struc->SubfuncIndex + 8), Struc->ParamBuffer, (Struc->ParamSize + 3) & ~3u); Struc->RetVal = 0; Struc->ApiRetVal = result; return result; }

__int64 __fastcall Invoke(__int64 (*Ptr)(void), _QWORD *ParamBuffer, unsigned int ParamSize) { // [COLLAPSED LOCAL DECLARATIONS. PRESS KEYPAD CTRL-"+" TO EXPAND] v3 = ParamSize >> 3; if ( !v3 ) return Ptr(); v4 = v3 - 1; if ( !v4 ) return (Ptr)(*ParamBuffer); v5 = v4 - 1; if ( !v5 ) return (Ptr)(*ParamBuffer, ParamBuffer[1]); v6 = v5 - 1; if ( !v6 ) return (Ptr)(*ParamBuffer, ParamBuffer[1], ParamBuffer[2]); v7 = v6 - 1; if ( !v7 ) return (Ptr)(*ParamBuffer, ParamBuffer[1], ParamBuffer[2], ParamBuffer[3]); v8 = v7 - 1; if ( !v8 ) return (Ptr)(*ParamBuffer, ParamBuffer[1], ParamBuffer[2], ParamBuffer[3], ParamBuffer[4]); v9 = v8 - 1; if ( !v9 ) return (Ptr)(*ParamBuffer, ParamBuffer[1], ParamBuffer[2], ParamBuffer[3], ParamBuffer[4], ParamBuffer[5]); if ( v9 == 1 ) return (Ptr)( *ParamBuffer, ParamBuffer[1], ParamBuffer[2], ParamBuffer[3], ParamBuffer[4], ParamBuffer[5], ParamBuffer[6]); return 0; }

void *__cdecl AllocatePoolWithAlign(UINTN AllocationSize, UINTN Align) { // [COLLAPSED LOCAL DECLARATIONS. PRESS KEYPAD CTRL-"+" TO EXPAND] Align_1 = Align; Size = AllocationSize; Memory = 0xFFFFFFFF; gFlag = 0; if ( (gBS_0->AllocatePages(AllocateMaxAddress, EfiRuntimeServicesData, 0x10, &Memory) & 0x8000000000000000) != 0 && (gBS_0->AllocatePages(AllocateAnyPages, EfiRuntimeServicesData, 0x10, &Memory) & 0x8000000000000000) != 0 ) { return 0; } gMem = Memory; gBS_0->SetMem(Memory, 0x10000, 0); qword_BF98 = 0; qword_BFA8 = 0xFFFF; v5 = 0 % Align_1; if ( v5 ) v6 = Align_1 - v5; else v6 = 0; gMem = v6 + Size; return (v6 & -(v6 + Size < 0xFFFF)); }

Disclosure Activity

Date

Dell PSIRT is notified

2021-12-08

Dell PSIRT confirmed reported issue

2022-02-25

Dell PSIRT assigned CVE number

2022-02-25

Dell PSIRT provide patch release

2022-02-25

BINARLY public disclosure date

2022-03-10

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Potential Impact

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Vulnerability Information

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Affected Intel firmware

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Vulnerability description

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Disclosure timeline

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Acknowledgements

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Get started today, Ship and Buy Software You Can Prove Is Safe

Potential Impact

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Vulnerability Information

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Affected Intel firmware

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Vulnerability description

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Disclosure timeline

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Acknowledgements

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Get started today, Ship and Buy Software You Can Prove Is Safe