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am b1bfa795: Merge "Allow sharing the RELRO section via a file."

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* commit 'b1bfa7956c56c28b8c914e6606df191e094e7b42':
  Allow sharing the RELRO section via a file.
This commit is contained in:
Torne (Richard Coles) 2014-04-22 13:32:01 +00:00 committed by Android Git Automerger
commit d56dd74036
5 changed files with 226 additions and 6 deletions
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18
libc/include/android/dlext.h
View File

@ -36,15 +36,31 @@ enum {
*/
ANDROID_DLEXT_RESERVED_ADDRESS_HINT = 0x2,
/* When set, write the GNU RELRO section of the mapped library to relro_fd
* after relocation has been performed, to allow it to be reused by another
* process loading the same library at the same address. This implies
* ANDROID_DLEXT_USE_RELRO.
*/
ANDROID_DLEXT_WRITE_RELRO = 0x4,
/* When set, compare the GNU RELRO section of the mapped library to relro_fd
* after relocation has been performed, and replace any relocated pages that
* are identical with a version mapped from the file.
*/
ANDROID_DLEXT_USE_RELRO = 0x8,
/* Mask of valid bits */
ANDROID_DLEXT_VALID_FLAG_BITS = ANDROID_DLEXT_RESERVED_ADDRESS |
ANDROID_DLEXT_RESERVED_ADDRESS_HINT,
ANDROID_DLEXT_RESERVED_ADDRESS_HINT |
ANDROID_DLEXT_WRITE_RELRO |
ANDROID_DLEXT_USE_RELRO,
};
typedef struct {
int flags;
void* reserved_addr;
size_t reserved_size;
int relro_fd;
} android_dlextinfo;
extern void* android_dlopen_ext(const char* filename, int flag, const android_dlextinfo* extinfo);

27
linker/linker.cpp
View File

@ -65,7 +65,7 @@
* and NOEXEC
*/
static bool soinfo_link_image(soinfo* si);
static bool soinfo_link_image(soinfo* si, const android_dlextinfo* extinfo);
static ElfW(Addr) get_elf_exec_load_bias(const ElfW(Ehdr)* elf);
// We can't use malloc(3) in the dynamic linker. We use a linked list of anonymous
@ -760,7 +760,7 @@ static soinfo* find_library_internal(const char* name, const android_dlextinfo*
TRACE("[ find_library_internal base=%p size=%zu name='%s' ]",
reinterpret_cast<void*>(si->base), si->size, si->name);
if (!soinfo_link_image(si)) {
if (!soinfo_link_image(si, extinfo)) {
munmap(reinterpret_cast<void*>(si->base), si->size);
soinfo_free(si);
return NULL;
@ -1566,7 +1566,7 @@ static int nullify_closed_stdio() {
return return_value;
}
static bool soinfo_link_image(soinfo* si) {
static bool soinfo_link_image(soinfo* si, const android_dlextinfo* extinfo) {
/* "base" might wrap around UINT32_MAX. */
ElfW(Addr) base = si->load_bias;
const ElfW(Phdr)* phdr = si->phdr;
@ -1904,6 +1904,23 @@ static bool soinfo_link_image(soinfo* si) {
return false;
}
/* Handle serializing/sharing the RELRO segment */
if (extinfo && (extinfo->flags & ANDROID_DLEXT_WRITE_RELRO)) {
if (phdr_table_serialize_gnu_relro(si->phdr, si->phnum, si->load_bias,
extinfo->relro_fd) < 0) {
DL_ERR("failed serializing GNU RELRO section for \"%s\": %s",
si->name, strerror(errno));
return false;
}
} else if (extinfo && (extinfo->flags & ANDROID_DLEXT_USE_RELRO)) {
if (phdr_table_map_gnu_relro(si->phdr, si->phnum, si->load_bias,
extinfo->relro_fd) < 0) {
DL_ERR("failed mapping GNU RELRO section for \"%s\": %s",
si->name, strerror(errno));
return false;
}
}
notify_gdb_of_load(si);
return true;
}
@ -2057,7 +2074,7 @@ static ElfW(Addr) __linker_init_post_relocation(KernelArgumentBlock& args, ElfW(
somain = si;
if (!soinfo_link_image(si)) {
if (!soinfo_link_image(si, NULL)) {
__libc_format_fd(2, "CANNOT LINK EXECUTABLE: %s\n", linker_get_error_buffer());
exit(EXIT_FAILURE);
}
@ -2174,7 +2191,7 @@ extern "C" ElfW(Addr) __linker_init(void* raw_args) {
linker_so.phnum = elf_hdr->e_phnum;
linker_so.flags |= FLAG_LINKER;
if (!soinfo_link_image(&linker_so)) {
if (!soinfo_link_image(&linker_so, NULL)) {
// It would be nice to print an error message, but if the linker
// can't link itself, there's no guarantee that we'll be able to
// call write() (because it involves a GOT reference). We may as

126
linker/linker_phdr.cpp
View File

@ -31,6 +31,9 @@
#include <errno.h>
#include <machine/exec.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include "linker.h"
#include "linker_debug.h"
@ -523,6 +526,129 @@ int phdr_table_protect_gnu_relro(const ElfW(Phdr)* phdr_table, size_t phdr_count
return _phdr_table_set_gnu_relro_prot(phdr_table, phdr_count, load_bias, PROT_READ);
}
/* Serialize the GNU relro segments to the given file descriptor. This can be
* performed after relocations to allow another process to later share the
* relocated segment, if it was loaded at the same address.
*
* Input:
* phdr_table -> program header table
* phdr_count -> number of entries in tables
* load_bias -> load bias
* fd -> writable file descriptor to use
* Return:
* 0 on error, -1 on failure (error code in errno).
*/
int phdr_table_serialize_gnu_relro(const ElfW(Phdr)* phdr_table, size_t phdr_count, ElfW(Addr) load_bias,
int fd) {
const ElfW(Phdr)* phdr = phdr_table;
const ElfW(Phdr)* phdr_limit = phdr + phdr_count;
ssize_t file_offset = 0;
for (phdr = phdr_table; phdr < phdr_limit; phdr++) {
if (phdr->p_type != PT_GNU_RELRO) {
continue;
}
ElfW(Addr) seg_page_start = PAGE_START(phdr->p_vaddr) + load_bias;
ElfW(Addr) seg_page_end = PAGE_END(phdr->p_vaddr + phdr->p_memsz) + load_bias;
ssize_t size = seg_page_end - seg_page_start;
ssize_t written = TEMP_FAILURE_RETRY(write(fd, reinterpret_cast<void*>(seg_page_start), size));
if (written != size) {
return -1;
}
void* map = mmap(reinterpret_cast<void*>(seg_page_start), size, PROT_READ,
MAP_PRIVATE|MAP_FIXED, fd, file_offset);
if (map == MAP_FAILED) {
return -1;
}
file_offset += size;
}
return 0;
}
/* Where possible, replace the GNU relro segments with mappings of the given
* file descriptor. This can be performed after relocations to allow a file
* previously created by phdr_table_serialize_gnu_relro in another process to
* replace the dirty relocated pages, saving memory, if it was loaded at the
* same address. We have to compare the data before we map over it, since some
* parts of the relro segment may not be identical due to other libraries in
* the process being loaded at different addresses.
*
* Input:
* phdr_table -> program header table
* phdr_count -> number of entries in tables
* load_bias -> load bias
* fd -> readable file descriptor to use
* Return:
* 0 on error, -1 on failure (error code in errno).
*/
int phdr_table_map_gnu_relro(const ElfW(Phdr)* phdr_table, size_t phdr_count, ElfW(Addr) load_bias,
int fd) {
// Map the file at a temporary location so we can compare its contents.
struct stat file_stat;
if (TEMP_FAILURE_RETRY(fstat(fd, &file_stat)) != 0) {
return -1;
}
off_t file_size = file_stat.st_size;
void* temp_mapping = mmap(NULL, file_size, PROT_READ, MAP_PRIVATE, fd, 0);
if (temp_mapping == MAP_FAILED) {
return -1;
}
size_t file_offset = 0;
// Iterate over the relro segments and compare/remap the pages.
const ElfW(Phdr)* phdr = phdr_table;
const ElfW(Phdr)* phdr_limit = phdr + phdr_count;
for (phdr = phdr_table; phdr < phdr_limit; phdr++) {
if (phdr->p_type != PT_GNU_RELRO) {
continue;
}
ElfW(Addr) seg_page_start = PAGE_START(phdr->p_vaddr) + load_bias;
ElfW(Addr) seg_page_end = PAGE_END(phdr->p_vaddr + phdr->p_memsz) + load_bias;
char* file_base = static_cast<char*>(temp_mapping) + file_offset;
char* mem_base = reinterpret_cast<char*>(seg_page_start);
size_t match_offset = 0;
size_t size = seg_page_end - seg_page_start;
while (match_offset < size) {
// Skip over dissimilar pages.
while (match_offset < size &&
memcmp(mem_base + match_offset, file_base + match_offset, PAGE_SIZE) != 0) {
match_offset += PAGE_SIZE;
}
// Count similar pages.
size_t mismatch_offset = match_offset;
while (mismatch_offset < size &&
memcmp(mem_base + mismatch_offset, file_base + mismatch_offset, PAGE_SIZE) == 0) {
mismatch_offset += PAGE_SIZE;
}
// Map over similar pages.
if (mismatch_offset > match_offset) {
void* map = mmap(mem_base + match_offset, mismatch_offset - match_offset,
PROT_READ, MAP_PRIVATE|MAP_FIXED, fd, match_offset);
if (map == MAP_FAILED) {
munmap(temp_mapping, file_size);
return -1;
}
}
match_offset = mismatch_offset;
}
// Add to the base file offset in case there are multiple relro segments.
file_offset += size;
}
munmap(temp_mapping, file_size);
return 0;
}
#if defined(__arm__)
# ifndef PT_ARM_EXIDX

5
linker/linker_phdr.h
View File

@ -89,6 +89,11 @@ int phdr_table_unprotect_segments(const ElfW(Phdr)* phdr_table, size_t phdr_coun
int phdr_table_protect_gnu_relro(const ElfW(Phdr)* phdr_table, size_t phdr_count, ElfW(Addr) load_bias);
int phdr_table_serialize_gnu_relro(const ElfW(Phdr)* phdr_table, size_t phdr_count, ElfW(Addr) load_bias,
int fd);
int phdr_table_map_gnu_relro(const ElfW(Phdr)* phdr_table, size_t phdr_count, ElfW(Addr) load_bias,
int fd);
#if defined(__arm__)
int phdr_table_get_arm_exidx(const ElfW(Phdr)* phdr_table, size_t phdr_count, ElfW(Addr) load_bias,

56
tests/dlext_test.cpp
View File

@ -17,8 +17,14 @@
#include <gtest/gtest.h>
#include <dlfcn.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <android/dlext.h>
#include <sys/mman.h>
#include <sys/wait.h>
#define ASSERT_DL_NOTNULL(ptr) \
@ -27,10 +33,14 @@
#define ASSERT_DL_ZERO(i) \
ASSERT_EQ(0, i) << "dlerror: " << dlerror()
#define ASSERT_NOERROR(i) \
ASSERT_NE(-1, i) << "errno: " << strerror(errno)
typedef int (*fn)(void);
#define LIBNAME "libdlext_test.so"
#define LIBSIZE 1024*1024 // how much address space to reserve for it
#define RELRO_FILE "/data/local/tmp/libdlext_test.relro"
class DlExtTest : public ::testing::Test {
@ -134,3 +144,49 @@ TEST_F(DlExtTest, ReservedHintTooSmall) {
reinterpret_cast<char*>(start) + PAGE_SIZE));
EXPECT_EQ(4, f());
}
TEST_F(DlExtTest, RelroShareChildWrites) {
void* start = mmap(NULL, LIBSIZE, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS,
-1, 0);
ASSERT_TRUE(start != MAP_FAILED);
android_dlextinfo extinfo;
extinfo.reserved_addr = start;
extinfo.reserved_size = LIBSIZE;
int relro_fd;
relro_fd = open(RELRO_FILE, O_CREAT | O_RDWR | O_TRUNC, 0644);
extinfo.flags = ANDROID_DLEXT_RESERVED_ADDRESS | ANDROID_DLEXT_WRITE_RELRO;
ASSERT_NOERROR(relro_fd);
extinfo.relro_fd = relro_fd;
pid_t pid = fork();
if (pid == 0) {
// child process
void* handle = android_dlopen_ext(LIBNAME, RTLD_NOW, &extinfo);
if (handle == NULL) {
fprintf(stderr, "in child: %s\n", dlerror());
exit(1);
}
exit(0);
}
// continuing in parent
ASSERT_NOERROR(close(relro_fd));
ASSERT_NOERROR(pid);
int status;
ASSERT_EQ(pid, waitpid(pid, &status, 0));
ASSERT_TRUE(WIFEXITED(status));
ASSERT_EQ(0, WEXITSTATUS(status));
relro_fd = open(RELRO_FILE, O_RDONLY);
ASSERT_NOERROR(relro_fd);
extinfo.flags = ANDROID_DLEXT_RESERVED_ADDRESS | ANDROID_DLEXT_USE_RELRO;
extinfo.relro_fd = relro_fd;
handle_ = android_dlopen_ext(LIBNAME, RTLD_NOW, &extinfo);
ASSERT_NOERROR(close(relro_fd));
ASSERT_DL_NOTNULL(handle_);
fn f = reinterpret_cast<fn>(dlsym(handle_, "getRandomNumber"));
ASSERT_DL_NOTNULL(f);
EXPECT_EQ(4, f());
}