Merge "Add some slack at the end of large allocations when target SDK level < S." am: 6ba27e04df

Original change: https://android-review.googlesource.com/c/platform/bionic/+/1621044

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I4c153c044cfa38e432e3a1e7b6eaca6a7cb8e761

libc/bionic/libc_init_common.cpp

@@ -132,6 +132,14 @@ void __libc_init_fork_handler() {
   pthread_atfork(arc4random_fork_handler, _thread_arc4_unlock, _thread_arc4_unlock);
 }
 
+extern "C" void scudo_malloc_set_add_large_allocation_slack(int add_slack);
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE void __libc_set_target_sdk_version(int target __unused) {
+#if defined(USE_SCUDO)
+  scudo_malloc_set_add_large_allocation_slack(target < __ANDROID_API_S__);
+#endif
+}
+
 __noreturn static void __early_abort(int line) {
   // We can't write to stdout or stderr because we're aborting before we've checked that
   // it's safe for us to use those file descriptors. We probably can't strace either, so

libc/bionic/libc_init_common.h

@@ -66,4 +66,6 @@ __LIBC_HIDDEN__ void __libc_init_AT_SECURE(char** envp);
 // pthread_atfork may call malloc() during its once-init.
 __LIBC_HIDDEN__ void __libc_init_fork_handler();
 
+__LIBC_HIDDEN__ void __libc_set_target_sdk_version(int target);
+
 #endif

libc/bionic/libc_init_dynamic.cpp

@@ -46,6 +46,7 @@
 #include <elf.h>
 #include "libc_init_common.h"
 
+#include "private/bionic_defs.h"
 #include "private/bionic_elf_tls.h"
 #include "private/bionic_globals.h"
 #include "platform/bionic/macros.h"
@@ -107,6 +108,8 @@ static void __libc_preinit_impl() {
   __libc_shared_globals()->unload_hook = __hwasan_library_unloaded;
 #endif
 
+  __libc_shared_globals()->set_target_sdk_version_hook = __libc_set_target_sdk_version;
+
   netdClientInit();
 }
 

libc/bionic/libc_init_static.cpp

@@ -400,6 +400,7 @@ extern "C" int android_get_application_target_sdk_version() {
 
 extern "C" void android_set_application_target_sdk_version(int target) {
   g_target_sdk_version = target;
+  __libc_set_target_sdk_version(target);
 }
 
 // This function is called in the dynamic linker before ifunc resolvers have run, so this file is

libc/private/bionic_globals.h

@@ -95,9 +95,10 @@ struct libc_shared_globals {
   TlsModules tls_modules;
   BionicAllocator tls_allocator;
 
-  // Values passed from the HWASan runtime (via libc.so) to the loader.
+  // Values passed from libc.so to the loader.
   void (*load_hook)(ElfW(Addr) base, const ElfW(Phdr)* phdr, ElfW(Half) phnum) = nullptr;
   void (*unload_hook)(ElfW(Addr) base, const ElfW(Phdr)* phdr, ElfW(Half) phnum) = nullptr;
+  void (*set_target_sdk_version_hook)(int target) = nullptr;
 
   // Values passed from the linker to libc.so.
   const char* init_progname = nullptr;

linker/linker_sdk_versions.cpp

@@ -31,6 +31,8 @@
 #include <android/api-level.h>
 #include <android/fdsan.h>
 
+#include "private/bionic_globals.h"
+
 #include "linker.h"
 
 static std::atomic<int> g_target_sdk_version(__ANDROID_API__);
@@ -45,6 +47,9 @@ void set_application_target_sdk_version(int target) {
   if (target < 30) {
     android_fdsan_set_error_level_from_property(ANDROID_FDSAN_ERROR_LEVEL_WARN_ONCE);
   }
+  if (__libc_shared_globals()->set_target_sdk_version_hook) {
+    __libc_shared_globals()->set_target_sdk_version_hook(target);
+  }
 }
 
 int get_application_target_sdk_version() {

tests/malloc_test.cpp

@@ -46,6 +46,7 @@
 #if defined(__BIONIC__)
 
 #include "SignalUtils.h"
+#include "dlext_private.h"
 
 #include "platform/bionic/malloc.h"
 #include "platform/bionic/mte.h"
@@ -1351,3 +1352,22 @@ TEST(malloc, disable_mte) {
   GTEST_SKIP() << "bionic extension";
 #endif
 }
+
+TEST(malloc, allocation_slack) {
+#if defined(__BIONIC__)
+  bool allocator_scudo;
+  GetAllocatorVersion(&allocator_scudo);
+  if (!allocator_scudo) {
+    GTEST_SKIP() << "scudo allocator only test";
+  }
+
+  // Test that older target SDK levels let you access a few bytes off the end of
+  // a large allocation.
+  android_set_application_target_sdk_version(29);
+  auto p = std::make_unique<char[]>(131072);
+  volatile char *vp = p.get();
+  volatile char oob ATTRIBUTE_UNUSED = vp[131072];
+#else
+  GTEST_SKIP() << "bionic extension";
+#endif
+}