基于学习和分享的目的，你可以自行下载，随意进行更改，但需要注明出处，版权属于我个人所有。
实现原理和思路：
1、必须完全了解Android linker加载和解析so过程
2、仿照linker解析过程解析要进行hook的so
3、修改GOT条目对于segment属性为可写，替换GOT条目，修改回为原属性
该版本为很早以前版本，可能仅支持4.4和5.0，想支持更高版本，应该稍作修改就可以了。
另外ALOGI
///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
头文件
/*
*
* Android Got Hook
*
* Author : sp00f
* Version 0.1
*/
#ifndef GOTHOOK_H_
#define GOTHOOK_H_
#include <android/log.h>
#define ALOGI(...) ((void)__android_log_print(ANDROID_LOG_INFO, "LOG", __VA_ARGS__))
/**
* Function : GotHook
* @param libName - will got hook 's so name
* @param symbol - will hook import method symbol
* @param oldAddr - the method addr before hooked
* @param newAddr - will replace the new addr of the method
*
* @return success true ,else false
*/
bool gotHook(const char* libName, const char* symbol, void* oldAddr, void* newAddr);
#endif /* GOTHOOK_H_ */
实现源码：
/*
*
* Android Got Hook
*
* Author : sp00f
* Version 0.1
*/
#include "GotHook.h"
#include <fcntl.h>
#include <dlfcn.h>
#include <string.h>
#include <types.h>
#include <errno.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/exec_elf.h>
#include <elf.h>
#ifndef MAYBE_MAP_FLAG
#define MAYBE_MAP_FLAG(x,from,to) (((x) & (from)) ? (to) : 0)
#endif
#ifndef PFLAGS_TO_PROT
#define PFLAGS_TO_PROT(x) (MAYBE_MAP_FLAG((x), PF_X, PROT_EXEC) | \
MAYBE_MAP_FLAG((x), PF_R, PROT_READ) | \
MAYBE_MAP_FLAG((x), PF_W, PROT_WRITE))
#endif
#ifndef PAGE_START
#define PAGE_START(x) ((x) & PAGE_MASK)
#endif
#ifndef PAGE_OFFSET
#define PAGE_OFFSET(x) ((x) & ~PAGE_MASK)
#endif
#ifndef PAGE_END
#define PAGE_END(x) PAGE_START((x) + (PAGE_SIZE-1))
#endif
#ifndef SOINFO_NAME_LEN
#define SOINFO_NAME_LEN 128
#endif
#ifndef MAYBE_MAP_FLAG
#define MAYBE_MAP_FLAG(x,from,to) (((x) & (from)) ? (to) : 0)
#endif
#ifndef PFLAGS_TO_PROT
#define PFLAGS_TO_PROT(x) (MAYBE_MAP_FLAG((x), PF_X, PROT_EXEC) | \
MAYBE_MAP_FLAG((x), PF_R, PROT_READ) | \
MAYBE_MAP_FLAG((x), PF_W, PROT_WRITE))
#endif
#ifndef PAGE_START
#define PAGE_START(x) ((x) & PAGE_MASK)
#endif
#ifndef PAGE_OFFSET
#define PAGE_OFFSET(x) ((x) & ~PAGE_MASK)
#endif
#ifndef PAGE_END
#define PAGE_END(x) PAGE_START((x) + (PAGE_SIZE-1))
#endif
#ifndef SOINFO_NAME_LEN
#define SOINFO_NAME_LEN 128
#endif
// mips64 interprets Elf64_Rel structures' r_info field differently.
// bionic (like other C libraries) has macros that assume regular ELF files,
// but the dynamic linker needs to be able to load mips64 ELF files.
#if defined(__mips__) && defined(__LP64__)
#undef ELF64_R_SYM
#undef ELF64_R_TYPE
#undef ELF64_R_INFO
#define ELF64_R_SYM(info) (((info) >> 0) & 0xffffffff)
#define ELF64_R_SSYM(info) (((info) >> 32) & 0xff)
#define ELF64_R_TYPE3(info) (((info) >> 40) & 0xff)
#define ELF64_R_TYPE2(info) (((info) >> 48) & 0xff)
#define ELF64_R_TYPE(info) (((info) >> 56) & 0xff)
#endif
#if defined(__aarch64__) || defined(__x86_64__)
#define USE_RELA 1
#endif
typedef void (*linker_function_t)();
struct link_map {
Elf_Addr l_addr;
char* l_name;
Elf_Dyn* l_ld;
struct link_map* l_next;
struct link_map* l_prev;
};
struct soinfo {
char name[SOINFO_NAME_LEN];
const Elf_Phdr* phdr;
size_t phnum;
Elf_Addr entry;
Elf_Addr base;//vmap addr
size_t size;//mmap load size
#ifndef __LP64__
uint32_t unused1; // DO NOT USE, maintained for compatibility.
#endif
Elf_Dyn* dynamic;
#ifndef __LP64__
uint32_t unused2; // DO NOT USE, maintained for compatibility
uint32_t unused3; // DO NOT USE, maintained for compatibility
#endif
soinfo* next;
unsigned flags;
const char* strtab;
Elf_Sym* symtab;
size_t nbucket;
size_t nchain;
unsigned* bucket;
unsigned* chain;
#if defined(__mips__) || !defined(__LP64__)
// This is only used by mips and mips64, but needs to be here for
// all 32-bit architectures to preserve binary compatibility.
Elf_Addr** plt_got;
#endif
#if defined(USE_RELA)
Elf_RelA* plt_rela;
size_t plt_rela_count;
Elf_RelA* rela;
size_t rela_count;
#else
Elf_Rel* plt_rel;
size_t plt_rel_count;
Elf_Rel* rel;
size_t rel_count;
#endif
linker_function_t* preinit_array;
size_t preinit_array_count;
linker_function_t* init_array;
size_t init_array_count;
linker_function_t* fini_array;
size_t fini_array_count;
linker_function_t init_func;
linker_function_t fini_func;
#if defined(__arm__)
// ARM EABI section used for stack unwinding.
unsigned* ARM_exidx;
size_t ARM_exidx_count;
#elif defined(__mips__)
unsigned mips_symtabno;
unsigned mips_local_gotno;
unsigned mips_gotsym;
#endif
size_t ref_count;
struct link_map link_map_;
bool constructors_called;
// When you read a virtual address from the ELF file, add this
// value to get the corresponding address in the process' address space.
Elf_Addr load_bias;
#if !defined(__LP64__)
bool has_text_relocations;
#endif
bool has_DT_SYMBOLIC;
};
//exe maps
// b6ec9000-b6f0c000 r-xp 00000000 b3:1c 627097 /data/local/tmp/jiagu_art
// b6f0c000-b6f0f000 r--p 00042000 b3:1c 627097 /data/local/tmp/jiagu_art
// b6f0f000-b6f12000 rw-p 00045000 b3:1c 627097 /data/local/tmp/jiagu_art
//
// exe select soinfo last phdr start and end,it is different between exe phdr Segments and so phdr Segments
//
//
//@1 maybe has bug, i think process's so maps, always like :
//74ede000-74eea000 r-xp 00000000 b3:1c 48880 /data/app-lib/com.example.test-2/libnotify.so
//74eea000-74eeb000 r--p 0000b000 b3:1c 48880 /data/app-lib/com.example.test-2/libnotify.so
//74eeb000-74eec000 rw-p 0000c000 b3:1c 48880 /data/app-lib/com.example.test-2/libnotify.so
//so i select the mid segment (because plt got in this segment),and change it's prot
//at last i change it back
//i also found, when i change it back , the flags = PF_X not PF_R ,why ??
//@2 before this method , i change last two segments ,but when i changed it , the last two segments was combined into one segments
//so i use @1
//you can implement yours' ,like reading process's maps, and parsing the maps, than change the corrent segments.
//this is a test ,so i implement like @1 , some code was siphoned from linker code.
static int changeSegmentsProt(const Elf_Phdr* phdr_table, int phdr_count,
Elf_Addr load_bias, int extra_prot_flags, bool isSo) {
Elf_Addr prot_start = 0;
Elf_Addr prot_mid = 0;
Elf_Addr prot_end = 0;
int flags = 0;
if(isSo) {
for (size_t i = 0; i < phdr_count; ++i) {
const Elf_Phdr* phdr = &phdr_table[i];
// Segment addresses in memory.
Elf_Addr seg_start = phdr->p_vaddr + load_bias;
Elf_Addr seg_end = seg_start + phdr->p_memsz;
Elf_Addr seg_page_start = PAGE_START(seg_start);
Elf_Addr seg_page_end = PAGE_END(seg_end);
ALOGI("[*] seg_page_start = 0x%.16x , seg_page_end = 0x%.16x, length = 0x%.16x",
seg_page_start, seg_page_end, (seg_page_end - seg_page_start));
if (seg_page_start > prot_start)
prot_start = seg_page_start;
if (seg_page_end > prot_end)
prot_end = seg_page_end;
if (seg_page_end > prot_start && seg_page_end < prot_end) {
prot_mid = seg_page_end;
flags = PFLAGS_TO_PROT(phdr->p_flags);
}
}
} else {
const Elf_Phdr* phdr = &phdr_table[phdr_count-1];
// Segment addresses in memory.
Elf_Addr seg_start = phdr->p_vaddr + load_bias;
Elf_Addr seg_end = seg_start + phdr->p_memsz;
Elf_Addr seg_page_start = PAGE_START(seg_start);
Elf_Addr seg_page_end = PAGE_END(seg_end);
ALOGI("[*] seg_page_start = 0x%.16x , seg_page_end = 0x%.16x, length = 0x%.16x",
seg_page_start, seg_page_end, (seg_page_end - seg_page_start));
prot_start = seg_page_start;
prot_mid = seg_page_end;
flags = PFLAGS_TO_PROT(phdr->p_flags);
}
ALOGI("[+] prot_start = 0x%.16x , prot_mid = 0x%.16x, prot_end = 0x%.16x",
prot_start, prot_mid, prot_end);
int ret = -1;
if(extra_prot_flags == 0) {
ret = mprotect((void*) prot_start, (prot_mid - prot_start),
PROT_READ | extra_prot_flags);
} else {
ret = mprotect((void*) prot_start, (prot_mid - prot_start),
flags | extra_prot_flags );
}
if (ret < 0) {
return ret;
}
return 0;
}
#if defined(USE_RELA)
static bool isHookedSym(struct soinfo* si, const char* symbol, void* oldAddr,
void* newAddr, Elf_Sym* symtab, const char* strtab,
Elf_RelA* rel, size_t count) {
#else
static bool isHookedSym(struct soinfo* si, const char* symbol, void* oldAddr,
void* newAddr, Elf_Sym* symtab, const char* strtab,
Elf_Rel* rel, size_t count) {
#endif
ALOGI("[*] into isHookedSym");
bool isFoundSym = false;
for (size_t idx = 0; idx < count; ++idx, ++rel) {
unsigned type = ELF_R_TYPE(rel->r_info);
unsigned sym = ELF_R_SYM(rel->r_info);
Elf_Addr reloc = static_cast<Elf_Addr>(rel->r_offset + si->base);
char* sym_name = NULL;
if (type == 0) { // R_*_NONE
continue;
}
if (sym != 0) {
sym_name = (char *) (strtab + symtab[sym].st_name);
// ALOGI("[*] sym_name = %s", sym_name);
Elf_Addr addr = *reinterpret_cast<Elf_Addr*>(reloc);
const char* symname = const_cast<const char*>(sym_name);
if (strcmp(symname, symbol) == 0) {
*reinterpret_cast<Elf_Addr*>(reloc) = (Elf_Addr) newAddr;
*reinterpret_cast<Elf_Addr*>(oldAddr) = addr;
ALOGI("[+] sys name = %s , got old addr = 0x%.16x, ret orgi_addr = 0x%.16x, new addr = 0x%.16x",
sym_name, addr, *reinterpret_cast<Elf_Addr*>(oldAddr),
*reinterpret_cast<Elf_Addr*>(reloc));
isFoundSym = true;
break;
}
}
}
ALOGI("[*] return isHookedSym");
return isFoundSym;
}
bool gotHook(const char* libName, const char* symbol, void* oldAddr,
void* newAddr) {
bool isFoundSym = false;
bool isSo = true;
void* handle = dlopen(libName, RTLD_NOW);
if (!handle) {
ALOGI("[-] can't find so library %s", libName);
isSo = false;
}
if(!isSo) {
handle = dlopen("libdl.so", RTLD_NOW);
struct soinfo* oi = (struct soinfo*) handle;
while(oi) {
ALOGI("[*] so name=%s", oi->name);
if(strstr(oi->name, libName)) {
handle = (void*) oi;
break;
}
oi = oi->next;
}
if(!handle)
ALOGI("[-] can't find bin %s", libName);
}
struct soinfo* si = (struct soinfo*) handle;
Elf_Sym* symtab = si->symtab;
const char* strtab = si->strtab;
#if defined(USE_RELA)
Elf_RelA* rel = si->plt_rela;
size_t count = si->plt_rela_count;
#else
Elf_Rel* rel = si->plt_rel;
size_t count = si->plt_rel_count;
#endif
if(count == 0) {
#if defined(USE_RELA)
rel = si->rela;
count = si->rela_count;
#else
rel = si->rel;
count = si->rel_count;
#endif
}
ALOGI("[*] import sym count = %d", count);
if(count == 0)
return false;
ALOGI("[*] module base = %.16x, module size = %.16x" , si->base, si->size);
if (changeSegmentsProt(si->phdr, si->phnum, si->base, PROT_WRITE, isSo) < 0) {
ALOGI("[-] can't unprotect loadable segments for \"%s\": %s",
si->name, strerror(errno));
return false;
}
isFoundSym = isHookedSym(si, symbol, oldAddr,
newAddr, symtab, strtab,
rel,count) ;
if(!isFoundSym) {
#if defined(USE_RELA)
rel = si->rela;
count = si->rela_count;
#else
rel = si->rel;
count = si->rel_count;
#endif
isFoundSym = isHookedSym(si, symbol, oldAddr,
newAddr, symtab, strtab,
rel,count) ;
}
if (changeSegmentsProt(si->phdr, si->phnum, si->base, 0, isSo) < 0) {
ALOGI("[-] can't unprotect loadable segments for \"%s\": %s",
si->name, strerror(errno));
return false;
}
if(isSo)
dlclose(handle);
ALOGI("[*] hook %s ,sym %s is %d", libName, symbol, isFoundSym);
return isFoundSym;
}