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Keep the dynamic linker's soinfo pools mostly read-only.

Browse source 
We'll need a lot more refactoring of this code before we can reduce
the granularity, but this is a step forward.

Change-Id: I07061720e734b571a8399c1d5b4f2f35cd681307
This commit is contained in:
Elliott Hughes 2012-11-01 15:16:56 -07:00
parent 064f862d55
commit d23736e4f2
4 changed files with 253 additions and 241 deletions
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1
linker/debugger.cpp
View file

@ -32,7 +32,6 @@
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdbool.h>
#include <signal.h>
#include <sys/prctl.h>
#include <errno.h>

9
linker/dlfcn.cpp
View file

@ -57,13 +57,11 @@ const char* dlerror() {
void* dlopen(const char* filename, int flag) {
ScopedPthreadMutexLocker locker(&gDlMutex);
soinfo* result = find_library(filename);
soinfo* result = do_dlopen(filename);
if (result == NULL) {
__bionic_format_dlerror("dlopen failed", linker_get_error());
return NULL;
}
soinfo_call_constructors(result);
result->refcount++;
return result;
}
@ -139,7 +137,7 @@ int dladdr(const void* addr, Dl_info* info) {
int dlclose(void* handle) {
ScopedPthreadMutexLocker locker(&gDlMutex);
return soinfo_unload((soinfo*) handle);
return do_dlclose(reinterpret_cast<soinfo*>(handle));
}
#if defined(ANDROID_ARM_LINKER)
@ -236,7 +234,8 @@ soinfo libdl_info = {
refcount: 0,
{ l_addr: 0, l_name: 0, l_ld: 0, l_next: 0, l_prev: 0, },
constructors_called: 0, load_bias: 0,
constructors_called: false,
load_bias: 0,
has_text_relocations: false,
has_DT_SYMBOLIC: true,
};

327
linker/linker.cpp
View file

@ -31,7 +31,6 @@
#include <fcntl.h>
#include <linux/auxvec.h>
#include <pthread.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
@ -74,7 +73,6 @@
* and NOEXEC
*/
static bool soinfo_link_image(soinfo* si);
// We can't use malloc(3) in the dynamic linker. We use a linked list of anonymous
@ -293,6 +291,14 @@ static bool ensure_free_list_non_empty() {
return true;
}
static void set_soinfo_pool_protection(int protection) {
for (soinfo_pool_t* p = gSoInfoPools; p != NULL; p = p->next) {
if (mprotect(p, sizeof(*p), protection) == -1) {
abort(); // Can't happen.
}
}
}
static soinfo* soinfo_alloc(const char* name) {
if (strlen(name) >= SOINFO_NAME_LEN) {
DL_ERR("library name \"%s\" too long", name);
@ -833,20 +839,18 @@ static soinfo* load_library(const char* name) {
return si.release();
}
static soinfo *
init_library(soinfo *si)
{
/* At this point we know that whatever is loaded @ base is a valid ELF
* shared library whose segments are properly mapped in. */
TRACE("[ %5d init_library base=0x%08x sz=0x%08x name='%s') ]\n",
pid, si->base, si->size, si->name);
static soinfo* init_library(soinfo* si) {
// At this point we know that whatever is loaded @ base is a valid ELF
// shared library whose segments are properly mapped in.
TRACE("[ %5d init_library base=0x%08x sz=0x%08x name='%s') ]\n",
pid, si->base, si->size, si->name);
if (!soinfo_link_image(si)) {
munmap((void *)si->base, si->size);
return NULL;
}
if (!soinfo_link_image(si)) {
munmap((void *)si->base, si->size);
return NULL;
}
return si;
return si;
}
static soinfo *find_loaded_library(const char *name)
@ -868,63 +872,86 @@ static soinfo *find_loaded_library(const char *name)
return NULL;
}
soinfo *find_library(const char *name)
{
soinfo *si;
static soinfo* find_library_internal(const char* name) {
if (name == NULL) {
return somain;
}
if (name == NULL)
return somain;
si = find_loaded_library(name);
if (si != NULL) {
if(si->flags & FLAG_ERROR) {
DL_ERR("\"%s\" failed to load previously", name);
return NULL;
}
if(si->flags & FLAG_LINKED) return si;
DL_ERR("OOPS: recursive link to \"%s\"", si->name);
return NULL;
soinfo* si = find_loaded_library(name);
if (si != NULL) {
if (si->flags & FLAG_ERROR) {
DL_ERR("\"%s\" failed to load previously", name);
return NULL;
}
if (si->flags & FLAG_LINKED) {
return si;
}
DL_ERR("OOPS: recursive link to \"%s\"", si->name);
return NULL;
}
TRACE("[ %5d '%s' has not been loaded yet. Locating...]\n", pid, name);
si = load_library(name);
if (si == NULL)
return NULL;
return init_library(si);
TRACE("[ %5d '%s' has not been loaded yet. Locating...]\n", pid, name);
si = load_library(name);
if (si != NULL) {
si = init_library(si);
}
return si;
}
static void call_destructors(soinfo *si);
static soinfo* find_library(const char* name) {
soinfo* si = find_library_internal(name);
if (si != NULL) {
si->refcount++;
}
return si;
}
int soinfo_unload(soinfo* si) {
if (si->refcount == 1) {
TRACE("%5d unloading '%s'\n", pid, si->name);
call_destructors(si);
static int soinfo_unload(soinfo* si) {
if (si->refcount == 1) {
TRACE("%5d unloading '%s'\n", pid, si->name);
si->CallDestructors();
for (unsigned* d = si->dynamic; *d; d += 2) {
if(d[0] == DT_NEEDED){
soinfo *lsi = find_loaded_library(si->strtab + d[1]);
if (lsi) {
TRACE("%5d %s needs to unload %s\n", pid,
si->name, lsi->name);
soinfo_unload(lsi);
} else {
// TODO: should we return -1 in this case?
DL_ERR("\"%s\": could not unload dependent library",
si->name);
}
}
for (unsigned* d = si->dynamic; *d; d += 2) {
if (d[0] == DT_NEEDED) {
soinfo* lsi = find_loaded_library(si->strtab + d[1]);
if (lsi != NULL) {
TRACE("%5d %s needs to unload %s\n", pid, si->name, lsi->name);
soinfo_unload(lsi);
} else {
// TODO: should we return -1 in this case?
DL_ERR("\"%s\": could not unload dependent library", si->name);
}
munmap((char *)si->base, si->size);
notify_gdb_of_unload(si);
soinfo_free(si);
si->refcount = 0;
} else {
si->refcount--;
PRINT("%5d not unloading '%s', decrementing refcount to %d\n",
pid, si->name, si->refcount);
}
}
return 0;
munmap(reinterpret_cast<void*>(si->base), si->size);
notify_gdb_of_unload(si);
soinfo_free(si);
si->refcount = 0;
} else {
si->refcount--;
PRINT("%5d not unloading '%s', decrementing refcount to %d\n",
pid, si->name, si->refcount);
}
return 0;
}
soinfo* do_dlopen(const char* name) {
set_soinfo_pool_protection(PROT_READ | PROT_WRITE);
soinfo* si = find_library(name);
if (si != NULL) {
si->CallConstructors();
}
set_soinfo_pool_protection(PROT_READ);
return si;
}
int do_dlclose(soinfo* si) {
set_soinfo_pool_protection(PROT_READ | PROT_WRITE);
int result = soinfo_unload(si);
set_soinfo_pool_protection(PROT_READ);
return result;
}
/* TODO: don't use unsigned for addrs below. It works, but is not
@ -1270,106 +1297,89 @@ static int mips_relocate_got(soinfo* si, soinfo* needed[]) {
*
* DT_FINI_ARRAY must be parsed in reverse order.
*/
void soinfo::CallArray(const char* array_name UNUSED, unsigned* array, int count, bool reverse) {
if (array == NULL) {
return;
}
static void call_array(unsigned *ctor, int count, int reverse)
{
int n, inc = 1;
int step = 1;
if (reverse) {
array += (count-1);
step = -1;
}
if (reverse) {
ctor += (count-1);
inc = -1;
TRACE("[ %5d Calling %s @ %p [%d] for '%s' ]\n", pid, array_name, array, count, name);
for (int n = count; n > 0; n--) {
TRACE("[ %5d Looking at %s[%d] *%p == 0x%08x ]\n", pid, array_name, n, array, *array);
void (*func)() = (void (*)()) *array;
array += step;
if (((int) func == 0) || ((int) func == -1)) {
continue;
}
TRACE("[ %5d Calling func @ %p ]\n", pid, func);
func();
}
for(n = count; n > 0; n--) {
TRACE("[ %5d Looking at %s *0x%08x == 0x%08x ]\n", pid,
reverse ? "dtor" : "ctor",
(unsigned)ctor, (unsigned)*ctor);
void (*func)() = (void (*)()) *ctor;
ctor += inc;
if(((int) func == 0) || ((int) func == -1)) continue;
TRACE("[ %5d Calling func @ 0x%08x ]\n", pid, (unsigned)func);
func();
}
TRACE("[ %5d Done calling %s for '%s' ]\n", pid, array_name, name);
}
static void soinfo_call_preinit_constructors(soinfo *si)
{
TRACE("[ %5d Calling preinit_array @ 0x%08x [%d] for '%s' ]\n",
pid, (unsigned)si->preinit_array, si->preinit_array_count,
si->name);
call_array(si->preinit_array, si->preinit_array_count, 0);
TRACE("[ %5d Done calling preinit_array for '%s' ]\n", pid, si->name);
void soinfo::CallFunction(const char* function_name UNUSED, void (*function)()) {
if (function == NULL) {
return;
}
TRACE("[ %5d Calling %s @ %p for '%s' ]\n", pid, function_name, function, name);
function();
TRACE("[ %5d Done calling %s for '%s' ]\n", pid, function_name, name);
}
void soinfo_call_constructors(soinfo *si)
{
if (si->constructors_called)
return;
void soinfo::CallPreInitConstructors() {
CallArray("DT_PREINIT_ARRAY", preinit_array, preinit_array_count, false);
}
// Set this before actually calling the constructors, otherwise it doesn't
// protect against recursive constructor calls. One simple example of
// constructor recursion is the libc debug malloc, which is implemented in
// libc_malloc_debug_leak.so:
// 1. The program depends on libc, so libc's constructor is called here.
// 2. The libc constructor calls dlopen() to load libc_malloc_debug_leak.so.
// 3. dlopen() calls soinfo_call_constructors() with the newly created
// soinfo for libc_malloc_debug_leak.so.
// 4. The debug so depends on libc, so soinfo_call_constructors() is
// called again with the libc soinfo. If it doesn't trigger the early-
// out above, the libc constructor will be called again (recursively!).
si->constructors_called = 1;
void soinfo::CallConstructors() {
if (constructors_called) {
return;
}
if (!(si->flags & FLAG_EXE) && si->preinit_array) {
DL_ERR("shared library \"%s\" has a preinit_array table @ 0x%08x. "
"This is INVALID.", si->name, (unsigned) si->preinit_array);
}
// We set constructors_called before actually calling the constructors, otherwise it doesn't
// protect against recursive constructor calls. One simple example of constructor recursion
// is the libc debug malloc, which is implemented in libc_malloc_debug_leak.so:
// 1. The program depends on libc, so libc's constructor is called here.
// 2. The libc constructor calls dlopen() to load libc_malloc_debug_leak.so.
// 3. dlopen() calls the constructors on the newly created
// soinfo for libc_malloc_debug_leak.so.
// 4. The debug .so depends on libc, so CallConstructors is
// called again with the libc soinfo. If it doesn't trigger the early-
// out above, the libc constructor will be called again (recursively!).
constructors_called = true;
if (si->dynamic) {
unsigned *d;
for(d = si->dynamic; *d; d += 2) {
if(d[0] == DT_NEEDED){
soinfo* lsi = find_loaded_library(si->strtab + d[1]);
if (!lsi) {
DL_ERR("\"%s\": could not initialize dependent library",
si->name);
} else {
soinfo_call_constructors(lsi);
}
}
if (!(flags & FLAG_EXE) && preinit_array) {
DL_ERR("shared library \"%s\" has a preinit_array table @ %p", name, preinit_array);
return;
}
if (dynamic) {
for (unsigned* d = dynamic; *d; d += 2) {
if (d[0] == DT_NEEDED) {
soinfo* lsi = find_loaded_library(strtab + d[1]);
if (lsi == NULL) {
DL_ERR("\"%s\": could not initialize dependent library", name);
} else {
lsi->CallConstructors();
}
}
}
}
if (si->init_func) {
TRACE("[ %5d Calling init_func @ 0x%08x for '%s' ]\n", pid,
(unsigned)si->init_func, si->name);
si->init_func();
TRACE("[ %5d Done calling init_func for '%s' ]\n", pid, si->name);
}
if (si->init_array) {
TRACE("[ %5d Calling init_array @ 0x%08x [%d] for '%s' ]\n", pid,
(unsigned)si->init_array, si->init_array_count, si->name);
call_array(si->init_array, si->init_array_count, 0);
TRACE("[ %5d Done calling init_array for '%s' ]\n", pid, si->name);
}
CallFunction("DT_INIT", init_func);
CallArray("DT_INIT_ARRAY", init_array, init_array_count, false);
}
static void call_destructors(soinfo *si)
{
if (si->fini_array) {
TRACE("[ %5d Calling fini_array @ 0x%08x [%d] for '%s' ]\n", pid,
(unsigned)si->fini_array, si->fini_array_count, si->name);
call_array(si->fini_array, si->fini_array_count, 1);
TRACE("[ %5d Done calling fini_array for '%s' ]\n", pid, si->name);
}
if (si->fini_func) {
TRACE("[ %5d Calling fini_func @ 0x%08x for '%s' ]\n", pid,
(unsigned)si->fini_func, si->name);
si->fini_func();
TRACE("[ %5d Done calling fini_func for '%s' ]\n", pid, si->name);
}
void soinfo::CallDestructors() {
CallArray("DT_FINI_ARRAY", fini_array, fini_array_count, true);
CallFunction("DT_FINI", fini_func);
}
/* Force any of the closed stdin, stdout and stderr to be associated with
@ -1632,18 +1642,16 @@ static bool soinfo_link_image(soinfo* si) {
}
/* if this is the main executable, then load all of the preloads now */
if(si->flags & FLAG_EXE) {
int i;
if (si->flags & FLAG_EXE) {
memset(preloads, 0, sizeof(preloads));
for(i = 0; gLdPreloadNames[i] != NULL; i++) {
soinfo *lsi = find_library(gLdPreloadNames[i]);
if(lsi == 0) {
for (size_t i = 0; gLdPreloadNames[i] != NULL; i++) {
soinfo* lsi = find_library(gLdPreloadNames[i]);
if (lsi == NULL) {
strlcpy(tmp_err_buf, linker_get_error(), sizeof(tmp_err_buf));
DL_ERR("could not load library \"%s\" needed by \"%s\"; caused by %s",
gLdPreloadNames[i], si->name, tmp_err_buf);
return false;
}
lsi->refcount++;
preloads[i] = lsi;
}
}
@ -1652,17 +1660,16 @@ static bool soinfo_link_image(soinfo* si) {
pneeded = needed = (soinfo**) alloca((1 + dynamic_count) * sizeof(soinfo*));
for (unsigned* d = si->dynamic; *d; d += 2) {
if(d[0] == DT_NEEDED){
if (d[0] == DT_NEEDED) {
DEBUG("%5d %s needs %s\n", pid, si->name, si->strtab + d[1]);
soinfo *lsi = find_library(si->strtab + d[1]);
if(lsi == 0) {
soinfo* lsi = find_library(si->strtab + d[1]);
if (lsi == NULL) {
strlcpy(tmp_err_buf, linker_get_error(), sizeof(tmp_err_buf));
DL_ERR("could not load library \"%s\" needed by \"%s\"; caused by %s",
si->strtab + d[1], si->name, tmp_err_buf);
return false;
}
*pneeded++ = lsi;
lsi->refcount++;
}
}
*pneeded = NULL;
@ -1910,10 +1917,10 @@ static unsigned __linker_init_post_relocation(unsigned **elfdata, unsigned linke
exit(EXIT_FAILURE);
}
soinfo_call_preinit_constructors(si);
si->CallPreInitConstructors();
for (size_t i = 0; preloads[i] != NULL; ++i) {
soinfo_call_constructors(preloads[i]);
preloads[i]->CallConstructors();
}
/*After the link_image, the si->base is initialized.
@ -1922,7 +1929,7 @@ static unsigned __linker_init_post_relocation(unsigned **elfdata, unsigned linke
*for some arch like x86 could work correctly within so exe.
*/
map->l_addr = si->base;
soinfo_call_constructors(si);
si->CallConstructors();
#if TIMING
gettimeofday(&t1,NULL);
@ -2056,6 +2063,8 @@ extern "C" unsigned __linker_init(unsigned **elfdata) {
// the main part of the linker now.
unsigned start_address = __linker_init_post_relocation(elfdata, linker_addr);
set_soinfo_pool_protection(PROT_READ);
// Return the address that the calling assembly stub should jump to.
return start_address;
}

157
linker/linker.h
View file

@ -46,33 +46,29 @@
// itself at the start of a page.
#define PAGE_END(x) PAGE_START((x) + (PAGE_SIZE-1))
void debugger_init();
// Magic shared structures that GDB knows about.
/* magic shared structures that GDB knows about */
struct link_map
{
uintptr_t l_addr;
char * l_name;
uintptr_t l_ld;
struct link_map * l_next;
struct link_map * l_prev;
struct link_map {
uintptr_t l_addr;
char * l_name;
uintptr_t l_ld;
struct link_map * l_next;
struct link_map * l_prev;
};
// Values for r_debug->state
enum {
RT_CONSISTENT,
RT_ADD,
RT_DELETE
RT_CONSISTENT,
RT_ADD,
RT_DELETE
};
struct r_debug
{
int32_t r_version;
struct link_map * r_map;
void (*r_brk)(void);
int32_t r_state;
uintptr_t r_ldbase;
struct r_debug {
int32_t r_version;
struct link_map* r_map;
void (*r_brk)(void);
int32_t r_state;
uintptr_t r_ldbase;
};
#define FLAG_LINKED 0x00000001
@ -83,75 +79,83 @@ struct r_debug
#define SOINFO_NAME_LEN 128
struct soinfo {
char name[SOINFO_NAME_LEN];
const Elf32_Phdr *phdr;
int phnum;
unsigned entry;
unsigned base;
unsigned size;
char name[SOINFO_NAME_LEN];
const Elf32_Phdr* phdr;
int phnum;
unsigned entry;
unsigned base;
unsigned size;
int unused; // DO NOT USE, maintained for compatibility.
int unused; // DO NOT USE, maintained for compatibility.
unsigned *dynamic;
unsigned* dynamic;
unsigned unused2; // DO NOT USE, maintained for compatibility
unsigned unused3; // DO NOT USE, maintained for compatibility
unsigned unused2; // DO NOT USE, maintained for compatibility
unsigned unused3; // DO NOT USE, maintained for compatibility
soinfo *next;
unsigned flags;
soinfo* next;
unsigned flags;
const char *strtab;
Elf32_Sym *symtab;
const char* strtab;
Elf32_Sym* symtab;
unsigned nbucket;
unsigned nchain;
unsigned *bucket;
unsigned *chain;
unsigned nbucket;
unsigned nchain;
unsigned* bucket;
unsigned* chain;
unsigned *plt_got;
unsigned* plt_got;
Elf32_Rel *plt_rel;
unsigned plt_rel_count;
Elf32_Rel* plt_rel;
unsigned plt_rel_count;
Elf32_Rel *rel;
unsigned rel_count;
Elf32_Rel* rel;
unsigned rel_count;
unsigned *preinit_array;
unsigned preinit_array_count;
unsigned* preinit_array;
unsigned preinit_array_count;
unsigned *init_array;
unsigned init_array_count;
unsigned *fini_array;
unsigned fini_array_count;
unsigned* init_array;
unsigned init_array_count;
unsigned* fini_array;
unsigned fini_array_count;
void (*init_func)(void);
void (*fini_func)(void);
void (*init_func)();
void (*fini_func)();
#if defined(ANDROID_ARM_LINKER)
/* ARM EABI section used for stack unwinding. */
unsigned *ARM_exidx;
unsigned ARM_exidx_count;
// ARM EABI section used for stack unwinding.
unsigned* ARM_exidx;
unsigned ARM_exidx_count;
#elif defined(ANDROID_MIPS_LINKER)
#if 0
/* not yet */
unsigned *mips_pltgot
// Not yet.
unsigned* mips_pltgot
#endif
unsigned mips_symtabno;
unsigned mips_local_gotno;
unsigned mips_gotsym;
#endif
unsigned mips_symtabno;
unsigned mips_local_gotno;
unsigned mips_gotsym;
#endif /* ANDROID_*_LINKER */
unsigned refcount;
struct link_map linkmap;
unsigned refcount;
struct link_map linkmap;
int constructors_called;
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 */
Elf32_Addr load_bias;
// When you read a virtual address from the ELF file, add this
// value to get the corresponding address in the process' address space.
Elf32_Addr load_bias;
bool has_text_relocations;
bool has_DT_SYMBOLIC;
bool has_text_relocations;
bool has_DT_SYMBOLIC;
void CallConstructors();
void CallDestructors();
void CallPreInitConstructors();
private:
void CallArray(const char* array_name, unsigned* array, int count, bool reverse);
void CallFunction(const char* function_name, void (*function)());
};
extern soinfo libdl_info;
@ -203,16 +207,17 @@ extern soinfo libdl_info;
#define DT_PREINIT_ARRAYSZ 33
#endif
soinfo *find_library(const char *name);
Elf32_Sym *lookup(const char *name, soinfo **found, soinfo *start);
soinfo *find_containing_library(const void *addr);
const char *linker_get_error(void);
soinfo* do_dlopen(const char* name);
int do_dlclose(soinfo* si);
int soinfo_unload(soinfo* si);
Elf32_Sym *soinfo_find_symbol(soinfo* si, const void *addr);
Elf32_Sym *soinfo_lookup(soinfo *si, const char *name);
void soinfo_call_constructors(soinfo *si);
Elf32_Sym* lookup(const char* name, soinfo** found, soinfo* start);
soinfo* find_containing_library(const void* addr);
const char* linker_get_error();
Elf32_Sym* soinfo_find_symbol(soinfo* si, const void* addr);
Elf32_Sym* soinfo_lookup(soinfo* si, const char* name);
void debugger_init();
extern "C" void notify_gdb_of_libraries();
#endif