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Improve memory map tricks

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- In `unmap_all`, replace readable pages atomically with mmap + mremap
- Create new function `remap_all` to replace pages with equivalent
  anonymous copies to prevent simple maps name scanning
This commit is contained in:
topjohnwu 2021-09-22 19:14:05 -07:00
parent da38f59e62
commit 12647dcf30
3 changed files with 39 additions and 19 deletions
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1
native/jni/zygisk/entry.cpp
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@ -106,6 +106,7 @@ static void first_stage_entry() {
// Load second stage
setenv(INJECT_ENV_2, "1", 1);
void *handle = dlopen(path, RTLD_LAZY);
remap_all(path);
// Revert path to 1st stage lib
*(strrchr(path, '.') - 1) = '1';

3
native/jni/zygisk/inject.hpp
View File

@ -16,6 +16,9 @@ enum : int {
// Unmap all pages matching the name
void unmap_all(const char *name);
// Remap all matching pages with anonymous pages
void remap_all(const char *name);
// Get library name + offset (from start of ELF), given function address
uintptr_t get_function_off(int pid, uintptr_t addr, char *lib);

54
native/jni/zygisk/utils.cpp
View File

@ -12,15 +12,9 @@ struct map_info {
uintptr_t end;
uintptr_t off;
int perms;
char *path;
const char *path;
map_info() : start(0), end(0), off(0), perms(0), path(nullptr) {}
enum {
EXEC = (1 << 0),
WRITE = (1 << 1),
READ = (1 << 2),
};
};
} // namespace
@ -43,11 +37,11 @@ static void parse_maps(int pid, Func fn) {
// Parse permissions
if (perm[0] != '-')
info.perms |= map_info::READ;
info.perms |= PROT_READ;
if (perm[1] != '-')
info.perms |= map_info::WRITE;
info.perms |= PROT_WRITE;
if (perm[2] != '-')
info.perms |= map_info::EXEC;
info.perms |= PROT_EXEC;
info.path = line + path_off;
@ -55,24 +49,46 @@ static void parse_maps(int pid, Func fn) {
});
}
void unmap_all(const char *name) {
vector<map_info> unmaps;
parse_maps(getpid(), [=, &unmaps](map_info &info) -> bool {
static vector<map_info> find_maps(const char *name) {
vector<map_info> maps;
parse_maps(getpid(), [=, &maps](map_info &info) -> bool {
if (strcmp(info.path, name) == 0)
unmaps.emplace_back(info);
maps.emplace_back(info);
return true;
});
for (map_info &info : unmaps) {
return maps;
}
void unmap_all(const char *name) {
vector<map_info> maps = find_maps(name);
for (map_info &info : maps) {
void *addr = reinterpret_cast<void *>(info.start);
size_t size = info.end - info.start;
munmap(addr, size);
if (info.perms & map_info::READ) {
if (info.perms & PROT_READ) {
// Make sure readable pages are still readable
xmmap(addr, size, PROT_READ, MAP_ANONYMOUS | MAP_PRIVATE, 0, 0);
void *dummy = xmmap(nullptr, size, PROT_READ, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
mremap(dummy, size, size, MREMAP_MAYMOVE | MREMAP_FIXED, addr);
} else {
munmap(addr, size);
}
}
}
void remap_all(const char *name) {
vector<map_info> maps = find_maps(name);
for (map_info &info : maps) {
void *addr = reinterpret_cast<void *>(info.start);
size_t size = info.end - info.start;
void *copy = xmmap(nullptr, size, PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
if ((info.perms & PROT_READ) == 0) {
mprotect(addr, size, PROT_READ);
}
memcpy(copy, addr, size);
mremap(copy, size, size, MREMAP_MAYMOVE | MREMAP_FIXED, addr);
mprotect(addr, size, info.perms);
}
}
uintptr_t get_function_off(int pid, uintptr_t addr, char *lib) {
uintptr_t off = 0;
parse_maps(pid, [=, &off](map_info &info) -> bool {
@ -90,7 +106,7 @@ uintptr_t get_function_off(int pid, uintptr_t addr, char *lib) {
uintptr_t get_function_addr(int pid, const char *lib, uintptr_t off) {
uintptr_t addr = 0;
parse_maps(pid, [=, &addr](map_info &info) -> bool {
if (strcmp(info.path, lib) == 0 && (info.perms & map_info::EXEC)) {
if (strcmp(info.path, lib) == 0 && (info.perms & PROT_EXEC)) {
addr = info.start - info.off + off;
return false;
}