Simplify hooking implementation

minecraft-linux · Sep 25, 2021 · 45ab709 · 45ab709
1 parent 9eec9d0
commit 45ab709
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Showing 3 changed files with 46 additions and 21 deletions.
diff --git a/linker/linker.cpp b/linker/linker.cpp
@@ -663,7 +663,13 @@ class LoadTask {
     auto extinfo = this->get_extinfo();
     if(extinfo && extinfo->flags & ANDROID_DLEXT_MCPELAUNCHER_HOOKS) {
       for(auto hook = extinfo->mcpelauncher_hooks; hook->name; hook++) {
-        (si_->symbols[hook->name] = std::make_shared<ElfW(Sym)>())->st_value = (ElfW(Addr))hook->value - si_->load_bias;
+        auto entry = std::make_shared<soinfo::HookEntry>();
+        entry->symbol.st_value = (ElfW(Addr))hook->value - si_->load_bias;
+        entry->symbol.st_info = STB_GLOBAL << 4;
+        entry->symbol.st_shndx = 1;
+        hook->value = nullptr;
+        entry->orig = &hook->value;
+        si_->symbols[hook->name] = std::move(entry);
       }
     }
 
@@ -2278,6 +2284,16 @@ void* do_dlopen(const char* name, int flags,
            "... dlopen calling constructors: realpath=\"%s\", soname=\"%s\", handle=%p",
            si->get_realpath(), si->get_soname(), handle);
     si->call_constructors();
+    if(extinfo && extinfo->flags & ANDROID_DLEXT_MCPELAUNCHER_HOOKS) {
+      for(auto&& sym : si->symbols) {
+        // Check if this symbol isn't relocated do a fake lookup to enshure orig is set
+        if(sym.second->orig != nullptr && *sym.second->orig == 0) {
+          void* val;
+          do_dlsym(handle, sym.first.data(), nullptr, nullptr, &val);
+        }
+        sym.second->orig = nullptr;
+      }
+    }
     failure_guard.Disable();
     LD_LOG(kLogDlopen,
            "... dlopen successful: realpath=\"%s\", soname=\"%s\", handle=%p",
@@ -2858,7 +2874,11 @@ soinfo *soinfo::load_library(const char *name, const std::unordered_map<std::str
     // lib->symbols.reserve(symbols.size());
     for (auto&& s : symbols) {
       if(s.second) {
-        (lib->symbols[s.first] = std::make_shared<ElfW(Sym)>())->st_value = (ElfW(Addr))s.second;
+        auto entry = std::make_shared<soinfo::HookEntry>();
+        entry->symbol.st_value = (ElfW(Addr))s.second;
+        entry->symbol.st_info = STB_GLOBAL << 4;
+        entry->symbol.st_shndx = 1;
+        lib->symbols[s.first] = std::move(entry);
       } else {
         async_safe_format_log(2, "load_library", "Undefined symbol %s", s.first.c_str());
       }

diff --git a/linker/linker_soinfo.cpp b/linker/linker_soinfo.cpp
@@ -97,6 +97,10 @@ void SymbolLookupList::set_dt_symbolic_lib(soinfo* lib) {
   begin_ = lib ? &libs_[0] : &libs_[1];
 }
 
+bool SymbolLookupLib::needs_sysv_lookup() const {
+  return si_ != nullptr && (gnu_bloom_filter_ == nullptr || si_->symbols.size() > 0);
+}
+
 // Check whether a requested version matches the version on a symbol definition. There are a few
 // special cases:
 //  - If the defining DSO has no version info at all, then any version matches.
@@ -148,19 +152,6 @@ soinfo_do_lookup_impl(const char* name, const version_info* vi,
                    name, lib->si_->get_realpath(), reinterpret_cast<void*>(lib->si_->base));
       }
 
-      if (lib->si_->symbols.size()) {
-        // Custom overrides
-        auto sym = lib->si_->symbols.find(name);
-        if(sym != lib->si_->symbols.end()) {
-          // if(!strcmp("mcpelauncher_vlog", name)) {
-          //   // throw 0;
-          //   int i = 0;
-          // }
-          *si_found_in = lib->si_;
-          return sym->second.get();
-        }
-      }
-
       const uint32_t word_num = (hash / kBloomMaskBits) & lib->gnu_maskwords_;
       const ElfW(Addr) bloom_word = lib->gnu_bloom_filter_[word_num];
       const uint32_t h1 = hash % kBloomMaskBits;
@@ -338,19 +329,29 @@ SymbolLookupLib soinfo::get_lookup_lib() {
 
 const ElfW(Sym)* soinfo::find_symbol_by_name(SymbolName& symbol_name,
                                              const version_info* vi) const {
+  void** orig = nullptr;
+  ElfW(Sym)* ret = nullptr;
   if (this->symbols.size()) {
     // Custom Library
     auto sym = this->symbols.find(symbol_name.get_name());
     if(sym != this->symbols.end()) {
       auto n = symbol_name.get_name();
-
-      return sym->second.get();
+      orig = sym->second->orig;
+      ret = &sym->second->symbol;
     }
   }
   if(this->bucket_) {
-    return is_gnu_hash() ? gnu_lookup(symbol_name, vi) : elf_lookup(symbol_name, vi);
+    auto&& ret2 = is_gnu_hash() ? gnu_lookup(symbol_name, vi) : elf_lookup(symbol_name, vi);
+    if(!ret) {
+      return ret2;
+    } else {
+      if(orig != nullptr) {
+        *orig = ret2 ? (void*)(ret2->st_value + load_bias) : nullptr;
+      }
+      return ret;
+    }
   }
-  return (ElfW(Sym)*)nullptr;
+  return ret;
 }
 
 const ElfW(Sym)* soinfo::gnu_lookup(SymbolName& symbol_name, const version_info* vi) const {

diff --git a/linker/linker_soinfo.h b/linker/linker_soinfo.h
@@ -91,7 +91,7 @@ struct SymbolLookupLib {
 
   soinfo* si_ = nullptr;
 
-  bool needs_sysv_lookup() const { return si_ != nullptr && gnu_bloom_filter_ == nullptr; }
+  bool needs_sysv_lookup() const;
 };
 
 // A list of libraries to search for a symbol.
@@ -442,7 +442,11 @@ struct soinfo {
   std::vector<TlsDynamicResolverArg> tlsdesc_args_;
 
 public:
-  std::unordered_map<std::string, std::shared_ptr<ElfW(Sym)>> symbols;
+  struct HookEntry {
+    ElfW(Sym) symbol;
+    void** orig;
+  };
+  std::unordered_map<std::string, std::shared_ptr<HookEntry>> symbols;
 };
 
 // This function is used by dlvsym() to calculate hash of sym_ver