111 lines
3.1 KiB
C
111 lines
3.1 KiB
C
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/**
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* @file detour.c
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* @brief Detour hooking library source
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* @author 8dcc
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*
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* https://github.com/8dcc/detour-lib
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*/
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#include <stdint.h>
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#include <stdbool.h>
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#include <string.h>
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#include <unistd.h> /* getpagesize */
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#include <sys/mman.h> /* mprotect */
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#include "include/detour.h"
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#define PAGE_SIZE getpagesize()
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#define PAGE_MASK (~(PAGE_SIZE - 1))
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#define PAGE_ALIGN(x) ((x + PAGE_SIZE - 1) & PAGE_MASK)
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#define PAGE_ALIGN_DOWN(x) (PAGE_ALIGN(x) - PAGE_SIZE)
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static bool protect_addr(void* ptr, int new_flags) {
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void* p = (void*)PAGE_ALIGN_DOWN((detour_ptr_t)ptr);
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int pgsz = getpagesize();
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if (mprotect(p, pgsz, new_flags) == -1)
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return false;
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return true;
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}
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/*
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* 64 bits:
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* 0: 48 b8 45 55 46 84 45 movabs rax,0x454584465545
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* 7: 45 00 00
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* a: ff e0 jmp rax
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*
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* 32 bits:
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* 0: b8 01 00 00 00 mov eax,0x1
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* 5: ff e0 jmp eax
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*/
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#ifdef __i386__
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static uint8_t def_jmp_bytes[] = { 0xB8, 0x00, 0x00, 0x00, 0x00, 0xFF, 0xE0 };
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#define JMP_BYTES_PTR 1 /* Offset inside the array where the ptr should go */
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#else
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static uint8_t def_jmp_bytes[] = { 0x48, 0xB8, 0x00, 0x00, 0x00, 0x00,
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0x00, 0x00, 0x00, 0x00, 0xFF, 0xE0 };
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#define JMP_BYTES_PTR 2 /* Offset inside the array where the ptr should go */
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#endif
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void detour_init(detour_data_t* data, void* orig, void* hook) {
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data->detoured = false;
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data->orig = orig;
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data->hook = hook;
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/* Store the first N bytes of the original function, where N is the size of
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* the jmp instructions */
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memcpy(data->saved_bytes, orig, sizeof(data->saved_bytes));
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/* Default jmp bytes */
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memcpy(data->jmp_bytes, &def_jmp_bytes, sizeof(def_jmp_bytes));
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/* JMP_BYTES_PTR is defined bellow def_jmp_bytes, and it changes depending
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* on the arch.
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* We use "&hook" and not "hook" because we want the address of
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* the func, not the first bytes of it like before. */
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memcpy(&data->jmp_bytes[JMP_BYTES_PTR], &hook, sizeof(detour_ptr_t));
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}
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bool detour_add(detour_data_t* d) {
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/* Already detoured, nothing to do */
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if (d->detoured)
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return true;
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/* See util.c */
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if (!protect_addr(d->orig, PROT_READ | PROT_WRITE | PROT_EXEC))
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return false;
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/* Copy our jmp instruction with our hook address to the orig */
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memcpy(d->orig, d->jmp_bytes, sizeof(d->jmp_bytes));
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/* Restore old protection */
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if (protect_addr(d->orig, PROT_READ | PROT_EXEC)) {
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d->detoured = true;
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return true;
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}
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return false;
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}
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bool detour_del(detour_data_t* d) {
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/* Not detoured, nothing to do */
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if (!d->detoured)
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return true;
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/* See util.c */
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if (!protect_addr(d->orig, PROT_READ | PROT_WRITE | PROT_EXEC))
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return false;
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/* Restore the bytes that were at the start of orig (we saved on init) */
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memcpy(d->orig, d->saved_bytes, sizeof(d->saved_bytes));
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/* Restore old protection */
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if (protect_addr(d->orig, PROT_READ | PROT_EXEC)) {
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d->detoured = false;
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return true;
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}
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return false;
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}
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