/*
* Locate a symbol in an ELF image.
*/
int
elf32FindSymbolByName(struct ElfObject *o, const char *name,
const Elf32_Sym **symp, const char **namep)
{
struct Section *shdrs, *hash, *syms;
const char *symStrings;
const Elf32_Sym *sym;
Elf32_Word nbucket;
Elf32_Word nchain;
Elf32_Word i;
const Elf32_Word *buckets;
const Elf32_Word *chains;
const Elf32_Word *hashData;
unsigned long hashv;
shdrs = o->sectionHeaders;
/* First, search the hashed symbols in .dynsym. */
if (elf32FindSectionByName(o, ".hash", &hash) != -1) {
syms = &shdrs[hash->shdr.sh_link];
hashData = elf32MapSection(o, hash);
sym = elf32MapSection(o, syms);
symStrings = elf32MapSection(o, &shdrs[syms->shdr.sh_link]);
nbucket = hashData[0];
nchain = hashData[1];
buckets = hashData + 2;
chains = buckets + nbucket;
hashv = elfhash(name) % nbucket;
for (i = buckets[hashv]; i != STN_UNDEF; i = chains[i])
if (strcmp(symStrings + sym[i].st_name, name) == 0) {
*symp = sym + i;
if (namep)
*namep = symStrings + sym[i].st_name;
return (0);
}
} else if (elf32FindSectionByName(o, ".dynsym", &syms) != -1) {
/* No ".hash", but have ".dynsym": do linear search */
if (elf32LinearSymSearch(o, syms, name, symp, namep) != -1) {
return (0);
}
}
/* Do a linear search of ".symtab" if present */
if (elf32FindSectionByName(o, ".symtab", &syms) != -1 &&
elf32LinearSymSearch(o, syms, name, symp, namep) != -1) {
return (0);
}
return -1;
}
void
elfdynhash(void)
{
Sym *s, *sy, *dynstr;
int i, j, nbucket, b, nfile;
uint32 hc, *chain, *buckets;
int nsym;
char *name;
Elfaux **need;
Elflib *needlib;
Elflib *l;
Elfaux *x;
if(!iself)
return;
nsym = nelfsym;
s = lookup(".hash", 0);
s->type = SELFROSECT;
s->reachable = 1;
i = nsym;
nbucket = 1;
while(i > 0) {
++nbucket;
i >>= 1;
}
needlib = nil;
need = malloc(nsym * sizeof need[0]);
chain = malloc(nsym * sizeof chain[0]);
buckets = malloc(nbucket * sizeof buckets[0]);
if(need == nil || chain == nil || buckets == nil) {
cursym = nil;
diag("out of memory");
errorexit();
}
memset(need, 0, nsym * sizeof need[0]);
memset(chain, 0, nsym * sizeof chain[0]);
memset(buckets, 0, nbucket * sizeof buckets[0]);
for(sy=allsym; sy!=S; sy=sy->allsym) {
if (sy->dynid <= 0)
continue;
if(sy->dynimpvers)
need[sy->dynid] = addelflib(&needlib, sy->dynimplib, sy->dynimpvers);
name = sy->dynimpname;
if(name == nil)
name = sy->name;
hc = elfhash((uchar*)name);
b = hc % nbucket;
chain[sy->dynid] = buckets[b];
buckets[b] = sy->dynid;
}
adduint32(s, nbucket);
adduint32(s, nsym);
for(i = 0; i<nbucket; i++)
adduint32(s, buckets[i]);
for(i = 0; i<nsym; i++)
adduint32(s, chain[i]);
free(chain);
free(buckets);
// version symbols
dynstr = lookup(".dynstr", 0);
s = lookup(".gnu.version_r", 0);
i = 2;
nfile = 0;
for(l=needlib; l; l=l->next) {
nfile++;
// header
adduint16(s, 1); // table version
j = 0;
for(x=l->aux; x; x=x->next)
j++;
adduint16(s, j); // aux count
adduint32(s, addstring(dynstr, l->file)); // file string offset
adduint32(s, 16); // offset from header to first aux
if(l->next)
adduint32(s, 16+j*16); // offset from this header to next
else
adduint32(s, 0);
for(x=l->aux; x; x=x->next) {
x->num = i++;
// aux struct
adduint32(s, elfhash((uchar*)x->vers)); // hash
adduint16(s, 0); // flags
adduint16(s, x->num); // other - index we refer to this by
adduint32(s, addstring(dynstr, x->vers)); // version string offset
if(x->next)
adduint32(s, 16); // offset from this aux to next
else
adduint32(s, 0);
}
}
// version references
s = lookup(".gnu.version", 0);
for(i=0; i<nsym; i++) {
if(i == 0)
adduint16(s, 0); // first entry - no symbol
else if(need[i] == nil)
adduint16(s, 1); // global
else
adduint16(s, need[i]->num);
}
free(need);
s = lookup(".dynamic", 0);
elfverneed = nfile;
if(elfverneed) {
elfwritedynentsym(s, DT_VERNEED, lookup(".gnu.version_r", 0));
elfwritedynent(s, DT_VERNEEDNUM, nfile);
elfwritedynentsym(s, DT_VERSYM, lookup(".gnu.version", 0));
}
elfwritedynent(s, DT_NULL, 0);
}
int main(int argc ,char** argv)
{
Elf32_Ehdr ehdr;
Elf32_Phdr phdr;
Elf32_Word dyn_size,dyn_strsz;
Elf32_Off dyn_off;
Elf32_Dyn dyn;
Elf32_Addr dyn_sym,dyn_str,dyn_hash;
unsigned func_hash,nbucket,nchain,func_index;
char * ptr_dynstr = NULL;
char * ptr_func_content = NULL;
Elf32_Sym func_sym;
int flag = 0;
int i = 0;
char func_name[] = "getString";
if(argc < 2)
{
printf("input the so file\n");
return 0;
}
int fd = open(argv[1],O_RDWR);
if(fd < 0)
{
printf("open file failed\n");
goto _error;
}
lseek(fd,0,SEEK_SET);
if(read(fd,&ehdr,sizeof(Elf32_Ehdr)) != sizeof(Elf32_Ehdr))
{
printf("read elf header failed\n");
goto _error;
}
lseek(fd,ehdr.e_phoff,SEEK_SET);
for(i=0; i<ehdr.e_phnum;i++)
{
memset(&phdr,0,sizeof(phdr));
if(read(fd,&phdr,sizeof(Elf32_Phdr)) != sizeof(Elf32_Phdr))
{
printf("read segment failed\n");
goto _error;
}
if(phdr.p_type == PT_DYNAMIC)
{
dyn_off = phdr.p_offset;
dyn_size = phdr.p_filesz;
printf("find .dynamic section\n");
break;
}
}
lseek(fd,dyn_off,SEEK_SET);
//for(i = 0;i<dyn_size/sizeof(Elf32_Dyn);i++)
do{
if(read(fd,&dyn,sizeof(Elf32_Dyn)) != sizeof(Elf32_Dyn))
{
printf("read .dynamic failed\n");
goto _error;
}
if(dyn.d_tag == DT_SYMTAB)
{
flag |= SYMTAB;
dyn_sym = dyn.d_un.d_ptr;
}
if(dyn.d_tag == DT_STRTAB)
{
flag |= STRTAB;
dyn_str = dyn.d_un.d_ptr;
}
if(dyn.d_tag == DT_STRSZ)
{
flag |= STRSZ;
dyn_strsz = dyn.d_un.d_val;
}
if(dyn.d_tag == DT_HASH)
{
flag |= HASH;
dyn_hash = dyn.d_un.d_ptr;
}
} while(dyn.d_tag != DT_NULL);
if((flag & 0x0f) != 0x0f)
{
printf("find the needed dynamic section failed\n");
goto _error;
}
ptr_dynstr = (char*)malloc(dyn_strsz);
if(ptr_dynstr == NULL)
{
printf("malloc .dynstr failed\n");
goto _error;
}
lseek(fd,dyn_str,SEEK_SET);
if(read(fd,ptr_dynstr,dyn_strsz) != dyn_strsz)
{
printf("read .dynstr failed\n");
goto _error;
}
func_hash = elfhash(func_name);
lseek(fd,dyn_hash,SEEK_SET);
if(read(fd,&nbucket,4) != 4)
{
printf("read hash nbucket failed\n");
goto _error;
}
if(read(fd,&nchain,4) != 4)
{
printf("read hash nchain failed\n");
goto _error;
}
func_hash = func_hash%nbucket;
lseek(fd,func_hash*4,SEEK_CUR);
if(read(fd,&func_index,4) != 4)//索引是符号表或者chain
{
printf("read funck index failed\n");
goto _error;
}
lseek(fd,dyn_sym+func_index*sizeof(Elf32_Sym),SEEK_SET);
if(read(fd,&func_sym,sizeof(Elf32_Sym)) != sizeof(Elf32_Sym))
{
printf("read func sym entry failed\n'");
}
if(strcmp(ptr_dynstr+func_sym.st_name,func_name) != 0)
{
while(1) //纯C语言是没有true的
{
lseek(fd,dyn_hash+4*(2+nbucket+func_index),SEEK_SET);
if(read(fd,&func_index,4) != 4)
{
printf("read func index failed\n");
goto _error;
}
lseek(fd,dyn_sym + func_index*sizeof(Elf32_Sym),SEEK_SET);
memset(&func_sym,0,sizeof(Elf32_Sym));
if(read(fd,&func_sym,sizeof(Elf32_Sym)) != sizeof(Elf32_Sym))
{
goto _error;
}
if(strcmp(func_name,dyn_str+func_sym.st_name) == 0)
{
break;
}
}
}
printf("find target func addr: %x,sizeo:%x\n",func_sym.st_value,func_sym.st_size);
ptr_func_content = (char*)malloc(func_sym.st_size);
if(ptr_func_content == NULL)
{
printf("alloc for func failed\n");
goto _error;
}
lseek(fd,func_sym.st_value,SEEK_SET);
if(read(fd,ptr_func_content,func_sym.st_size) != func_sym.st_size)
{
printf("read func content failed\n");
goto _error;
}
for(i=0;i<func_sym.st_size;i++)
{
ptr_func_content[i] = ~ptr_func_content[i];
}
lseek(fd,func_sym.st_value,SEEK_SET);
if(write(fd,ptr_func_content,func_sym.st_size) != func_sym.st_size)
{
printf("write to func failed\n");
goto _error;
}
printf("Complete \n");
_error:
if(ptr_dynstr != NULL)
{
free(ptr_dynstr);
}
if(ptr_func_content != NULL)
{
free(ptr_func_content);
}
return 0;
}
unsigned libhook_addhook( const char *soname, const char *symbol, unsigned newval ) {
struct soinfo *si = NULL;
Elf32_Rel *rel = NULL;
Elf32_Sym *s = NULL;
unsigned int sym_offset = 0;
size_t i;
// HOOKLOG( "dlopen(%s)", soname );
// since we know the module is already loaded and mostly
// we DO NOT want its constructors to be called again,
// ise RTLD_NOLOAD to just get its soinfo address.
si = (struct soinfo *)dlopen( soname, 4 /* RTLD_NOLOAD */ );
// si = (struct soinfo *)dlopen( soname, 0 /* RTLD_NOLOAD */ );
if( !si ){
HOOKLOG( "dlopen error: %s.", dlerror() );
return 0;
}
// HOOKLOG( "libhook_addhook dlopen success [0x%X], soinfo_elf_lookup...",(unsigned int)si);
s = soinfo_elf_lookup( si, elfhash(symbol), symbol );
if( !s ){
return 0;
}
// HOOKLOG( "soinfo_elf_lookup = [0x%X]", (unsigned int)s);
sym_offset = s - si->symtab;
// HOOKLOG( "sym_offset = [0x%X]", sym_offset);
// loop reloc table to find the symbol by index
for( i = 0, rel = si->plt_rel; i < si->plt_rel_count; ++i, ++rel ) {
unsigned type = ELF32_R_TYPE(rel->r_info);
unsigned sym = ELF32_R_SYM(rel->r_info);
unsigned reloc = (unsigned)(rel->r_offset + si->base);
// HOOKLOG( "[%i] type/reloc/sym = [0x%X/0x%X/0x%X]", i, type, reloc, sym);
if( sym_offset == sym ) {
switch(type) {
case R_ARM_JUMP_SLOT:
// HOOKLOG( "found R_ARM_JUMP_SLOT at [0x%X]", reloc);
return libhook_patch_address( reloc, newval );
default:
HOOKLOG( "Expected R_ARM_JUMP_SLOT, found 0x%X", type );
}
}
}
// HOOKLOG( "find by index finished %i", 0);
unsigned original = 0;
// loop dyn reloc table
for( i = 0, rel = si->rel; i < si->rel_count; ++i, ++rel ) {
unsigned type = ELF32_R_TYPE(rel->r_info);
unsigned sym = ELF32_R_SYM(rel->r_info);
unsigned reloc = (unsigned)(rel->r_offset + si->base);
if( sym_offset == sym ) {
switch(type) {
case R_ARM_ABS32:
case R_ARM_GLOB_DAT:
original = libhook_patch_address( reloc, newval );
default:
HOOKLOG( "Expected R_ARM_ABS32 or R_ARM_GLOB_DAT, found 0x%X", type );
}
}
}
if( original == 0 ){
HOOKLOG( "Unable to find symbol in the reloc tables ( plt_rel_count=%u - rel_count=%u ).", si->plt_rel_count, si->rel_count );
}
return original;
}
