Add preliminary zygote code injection support

Prototyping the injection setup and a clean "self unloading" mechanism.

native/jni/inject/utils.cpp

@@ -0,0 +1,101 @@
+#include <utils.hpp>
+
+#include "inject.hpp"
+
+using namespace std;
+
+namespace {
+
+struct map_info {
+    uintptr_t start;
+    uintptr_t end;
+    int perms;
+    char *path;
+
+    map_info() : start(0), end(0), perms(0), path(nullptr) {}
+
+    enum {
+        EXEC = (1 << 0),
+        WRITE = (1 << 1),
+        READ = (1 << 2),
+    };
+};
+
+} // namespace
+
+template<typename Func>
+static void parse_maps(int pid, Func fn) {
+    char file[32];
+
+    // format: start-end perms offset dev inode path
+    sprintf(file, "/proc/%d/maps", pid);
+    file_readline(true, file, [=](string_view l) -> bool {
+        char *pos = (char *) l.data();
+        map_info info;
+
+        // Parse address hex strings
+        info.start = strtoul(pos, &pos, 16);
+        info.end = strtoul(++pos, &pos, 16);
+
+        // Parse permissions
+        if (*(++pos) != '-')
+            info.perms |= map_info::READ;
+        if (*(++pos) != '-')
+            info.perms |= map_info::WRITE;
+        if (*(++pos) != '-')
+            info.perms |= map_info::EXEC;
+        pos += 3;
+
+        // Skip everything except path
+        int path_off;
+        sscanf(pos, "%*s %*s %*s %n%*s", &path_off);
+        pos += path_off;
+        info.path = pos;
+
+        return fn(info);
+    });
+}
+
+void unmap_all(const char *name) {
+    vector<map_info> unmaps;
+    parse_maps(getpid(), [=, &unmaps](map_info &info) -> bool {
+        if (strcmp(info.path, name) == 0)
+            unmaps.emplace_back(info);
+        return true;
+    });
+    for (map_info &info : unmaps) {
+        void *addr = reinterpret_cast<void *>(info.start);
+        size_t size = info.end - info.start;
+        munmap(addr, size);
+        if (info.perms & map_info::READ) {
+            // Make sure readable pages are still readable
+            xmmap(addr, size, PROT_READ, MAP_ANONYMOUS | MAP_PRIVATE, 0, 0);
+        }
+    }
+}
+
+uintptr_t get_function_lib(uintptr_t addr, char *lib) {
+    uintptr_t base = 0;
+    parse_maps(getpid(), [=, &base](map_info &info) -> bool {
+        if (addr >= info.start && addr < info.end) {
+            if (lib)
+                strcpy(lib, info.path);
+            base = info.start;
+            return false;
+        }
+        return true;
+    });
+    return base;
+}
+
+uintptr_t get_remote_lib(int pid, const char *lib) {
+    uintptr_t base = 0;
+    parse_maps(pid, [=, &base](map_info &info) -> bool {
+        if (strcmp(info.path, lib) == 0 && (info.perms & map_info::EXEC)) {
+            base = info.start;
+            return false;
+        }
+        return true;
+    });
+    return base;
+}