[libc] implement secure random buffer filling with vDSO

libc/src/__support/OSUtil/linux/CMakeLists.txt

@@ -53,3 +53,4 @@ add_object_library(
     libc.src.errno.errno
     libc.src.sys.auxv.getauxval
 )
+

libc/src/__support/OSUtil/linux/aarch64/vdso.h

@@ -23,6 +23,8 @@ LIBC_INLINE constexpr cpp::string_view symbol_name(VDSOSym sym) {
     return "__kernel_clock_gettime";
   case VDSOSym::ClockGetRes:
     return "__kernel_clock_getres";
+  case VDSOSym::GetRandom:
+    return "__kernel_getrandom";
   default:
     return "";
   }

libc/src/__support/OSUtil/linux/vdso_sym.h

@@ -19,7 +19,6 @@ struct __kernel_timespec;
 struct timezone;
 struct riscv_hwprobe;
 struct getcpu_cache;
-struct cpu_set_t;
 // NOLINTEND(llvmlibc-implementation-in-namespace)
 
 namespace LIBC_NAMESPACE_DECL {
@@ -35,7 +34,8 @@ enum class VDSOSym {
   RTSigReturn,
   FlushICache,
   RiscvHwProbe,
-  VDSOSymCount
+  GetRandom,
+  VDSOSymCount,
 };
 
 template <VDSOSym sym> LIBC_INLINE constexpr auto dispatcher() {
@@ -58,8 +58,11 @@ template <VDSOSym sym> LIBC_INLINE constexpr auto dispatcher() {
   else if constexpr (sym == VDSOSym::FlushICache)
     return static_cast<void (*)(void *, void *, unsigned int)>(nullptr);
   else if constexpr (sym == VDSOSym::RiscvHwProbe)
-    return static_cast<int (*)(riscv_hwprobe *, size_t, size_t, cpu_set_t *,
+    return static_cast<int (*)(riscv_hwprobe *, size_t, size_t, void *,
                                unsigned)>(nullptr);
+  else if constexpr (sym == VDSOSym::GetRandom)
+    return static_cast<int (*)(void *, size_t, unsigned int, void *, size_t)>(
+        nullptr);
   else
     return static_cast<void *>(nullptr);
 }

libc/src/__support/OSUtil/linux/x86_64/vdso.h

@@ -29,6 +29,8 @@ LIBC_INLINE constexpr cpp::string_view symbol_name(VDSOSym sym) {
     return "__vdso_time";
   case VDSOSym::ClockGetRes:
     return "__vdso_clock_getres";
+  case VDSOSym::GetRandom:
+    return "__vdso_getrandom";
   default:
     return "";
   }

libc/src/__support/threads/thread.cpp

@@ -117,7 +117,7 @@ class ThreadAtExitCallbackMgr {
 
   int add_callback(AtExitCallback *callback, void *obj) {
     cpp::lock_guard lock(mtx);
-    return callback_list.push_back({callback, obj});
+    return callback_list.push_back({callback, obj}) ? 0 : -1;
   }
 
   void call() {
@@ -161,6 +161,10 @@ void call_atexit_callbacks(ThreadAttributes *attrib) {
   }
 }
 
+bool add_atexit_callback(void (*callback)(void *), void *obj) {
+  return atexit_callback_mgr.add_callback(callback, obj) == 0;
+}
+
 } // namespace internal
 
 cpp::optional<unsigned int> new_tss_key(TSSDtor *dtor) {

libc/src/__support/threads/thread.h

@@ -246,6 +246,9 @@ namespace internal {
 // returned by this function.
 ThreadAtExitCallbackMgr *get_thread_atexit_callback_mgr();
 
+// Add internal atexit callbacks.
+bool add_atexit_callback(void (*callback)(void *), void *obj);
+
 // Call the currently registered thread specific atexit callbacks. Useful for
 // implementing the thread_exit function.
 void call_atexit_callbacks(ThreadAttributes *attrib);

libc/src/stdlib/linux/CMakeLists.txt

@@ -9,3 +9,21 @@ add_entrypoint_object(
     libc.src.signal.raise
     libc.src.stdlib._Exit
 )
+
+add_object_library(
+    cprng
+  HDRS
+    cprng.h
+  SRCS
+    cprng.cpp
+  DEPENDS
+    libc.src.__support.common
+    libc.src.__support.OSUtil.linux.vdso
+    libc.src.__support.threads.callonce
+    libc.src.__support.threads.linux.raw_mutex
+    libc.src.__support.CPP.optional
+    libc.src.__support.CPP.new
+    libc.src.__support.threads.thread
+    libc.src.sys.auxv.getauxval
+    libc.src.stdlib.atexit
+)