Adding a stack protector for linux x86-64.

[tnv01]

Summary

Setting %fs:0x28 to a random value which is used as the stack protector cookie.

libc/startup/linux/x86_64/CMakeLists.txt

 add_startup_object(
   crt1
   SRC
     start.cpp
   DEPENDS
     libc.config.linux.app_h
     libc.include.sys_mman
     libc.include.sys_syscall
     libc.include.unistd
     libc.src.__support.threads.thread
     libc.src.__support.OSUtil.osutil
     libc.src.stdlib.exit
+    libc.src.stdlib.abort
     libc.src.stdlib.atexit
     libc.src.string.memory_utils.memcpy_implementation
     libc.src.unistd.environ
   COMPILE_OPTIONS
     -fno-omit-frame-pointer
     -ffreestanding # To avoid compiler warnings about calling the main function.
     -fno-builtin
 )

libc/startup/linux/x86_64/start.cpp

 //===-- Implementation of crt for x86_64 ----------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "config/linux/app.h"
 #include "src/__support/OSUtil/syscall.h"
 #include "src/__support/threads/thread.h"
+#include "src/stdlib/abort.h"
 #include "src/stdlib/atexit.h"
 #include "src/stdlib/exit.h"
 #include "src/string/memory_utils/memcpy_implementations.h"
 
 #include <asm/prctl.h>
 #include <linux/auxvec.h>
 #include <linux/elf.h>
 #include <stdint.h>
 #include <sys/mman.h>
 #include <sys/syscall.h>
 #include <unistd.h>
 
 extern "C" int main(int, char **, char **);
 
+extern "C" void __stack_chk_fail() { __llvm_libc::abort(); }
+
 namespace __llvm_libc {
 
 #ifdef SYS_mmap2
 static constexpr long mmapSyscallNumber = SYS_mmap2;
 #elif SYS_mmap
 static constexpr long mmapSyscallNumber = SYS_mmap;
 #else
 #error "mmap and mmap2 syscalls not available."
void init_tls(TLSDescriptor &tls_descriptor) {
   // We will assume the alignment is always a power of two.
   uintptr_t tlsSize = app.tls.size & -app.tls.align;
   if (tlsSize != app.tls.size)
     tlsSize += app.tls.align;
 
   // Per the x86_64 TLS ABI, the entry pointed to by the thread pointer is the
   // address of the TLS block. So, we add more size to accomodate this address
   // entry.
-  uintptr_t tlsSizeWithAddr = tlsSize + sizeof(uintptr_t);
+  // We also need to include space for the stack canary. The canary is at
+  // offset 0x28 (40) and is of size uintptr_t.
+  uintptr_t tlsSizeWithAddr = tlsSize + sizeof(uintptr_t) + 40;
 
   // We cannot call the mmap function here as the functions set errno on
   // failure. Since errno is implemented via a thread local variable, we cannot
   // use errno before TLS is setup.
   long mmapRetVal = __llvm_libc::syscall_impl(
       mmapSyscallNumber, nullptr, tlsSizeWithAddr, PROT_READ | PROT_WRITE,
       MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
   // We cannot check the return value with MAP_FAILED as that is the return
   // of the mmap function and not the mmap syscall.
   if (mmapRetVal < 0 && static_cast<uintptr_t>(mmapRetVal) > -app.pageSize)
     __llvm_libc::syscall_impl(SYS_exit, 1);
   uintptr_t *tlsAddr = reinterpret_cast<uintptr_t *>(mmapRetVal);
 
   // x86_64 TLS faces down from the thread pointer with the first entry
   // pointing to the address of the first real TLS byte.
   uintptr_t endPtr = reinterpret_cast<uintptr_t>(tlsAddr) + tlsSize;
   *reinterpret_cast<uintptr_t *>(endPtr) = endPtr;
 
   __llvm_libc::inline_memcpy(reinterpret_cast<char *>(tlsAddr),
                              reinterpret_cast<const char *>(app.tls.address),
                              app.tls.init_size);
+  uintptr_t *stackGuardAddr = reinterpret_cast<uintptr_t *>(endPtr + 40);
+  // Setting the stack guard to a random value.
+  // We cannot call the get_random function here as the function sets errno on
+  // failure. Since errno is implemented via a thread local variable, we cannot
+  // use errno before TLS is setup.
+  ssize_t stackGuardRetVal = __llvm_libc::syscall_impl<ssize_t>(
+      SYS_getrandom, reinterpret_cast<long>(stackGuardAddr), sizeof(uint64_t),
+      0);
+  if (stackGuardRetVal < 0)
+    __llvm_libc::syscall_impl(SYS_exit, 1);
 
   tls_descriptor = {tlsSizeWithAddr, uintptr_t(tlsAddr), endPtr};
   return;
 }
 
 void cleanup_tls(uintptr_t addr, uintptr_t size) {
   if (size == 0)
     return;

libc/test/integration/src/unistd/CMakeLists.txt

DEPENDS
     libc.src.pthread.pthread_atfork
     libc.src.signal.raise
     libc.src.sys.wait.wait
     libc.src.sys.wait.wait4
     libc.src.sys.wait.waitpid
     libc.src.unistd.fork
 )
 
+if((${LIBC_TARGET_OS} STREQUAL "linux") AND (${LIBC_TARGET_ARCHITECTURE_IS_X86}))
+  add_integration_test(
+    stack_smashing_test
+    SUITE
+      unistd-integration-tests
+    SRCS
+      stack_smashing_test.cpp
+    DEPENDS
+      libc.include.errno
+      libc.include.signal
+      libc.include.sys_wait
+      libc.include.unistd
+      libc.src.pthread.pthread_atfork
+      libc.src.signal.raise
+      libc.src.sys.wait.wait
+      libc.src.sys.wait.wait4
+      libc.src.sys.wait.waitpid
+      libc.src.unistd.fork
+    COMPILE_OPTIONS
+      -fstack-protector-all
+  )
+endif()
+
 add_executable(
   libc_execv_test_normal_exit
   EXCLUDE_FROM_ALL
   execv_test_normal_exit.cpp
 )
 set_target_properties(
   libc_execv_test_normal_exit
   PROPERTIES

libc/test/integration/src/unistd/stack_smashing_test.cpp

+//===--- Stack smashing test to check stack canary set up  ----------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/__support/CPP/string.h"
+#include "src/__support/OSUtil/io.h"
+#include "src/pthread/pthread_atfork.h"
+#include "src/signal/raise.h"
+#include "src/sys/wait/wait.h"
+#include "src/sys/wait/wait4.h"
+#include "src/sys/wait/waitpid.h"
+#include "src/unistd/fork.h"
+
+#include "test/IntegrationTest/test.h"
+
+#include <errno.h>
+#include <signal.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+void no_stack_smashing_normal_exit() {
+  pid_t pid = __llvm_libc::fork();
+  if (pid == 0) {
+    // Child process
+    char foo[30];
+    for (int i = 0; i < 30; i++)
+      foo[i] = 42;
+    return;
+  }
+  ASSERT_TRUE(pid > 0);
+  int status;
+  pid_t cpid = __llvm_libc::wait(&status);
+  ASSERT_TRUE(cpid > 0);
+  ASSERT_EQ(cpid, pid);
+  ASSERT_TRUE(WIFEXITED(status));
+}
+
+void stack_smashing_abort() {
+  pid_t pid = __llvm_libc::fork();
+  if (pid == 0) {
+    // Child process
+    char foo[30];
+    char *frame_ptr = static_cast<char *>(__builtin_frame_address(0));
+    char *cur_ptr = &foo[0];
+    // Corrupt the stack
+    while (cur_ptr != frame_ptr) {
+      *cur_ptr = 42;
+      cur_ptr++;
+    }
+    return;
+  }
+  ASSERT_TRUE(pid > 0);
+  int status;
+  pid_t cpid = __llvm_libc::wait(&status);
+  ASSERT_TRUE(cpid > 0);
+  ASSERT_EQ(cpid, pid);
+  ASSERT_TRUE(WTERMSIG(status) == SIGABRT);
+}
+
+TEST_MAIN(int argc, char **argv, char **envp) {
+  no_stack_smashing_normal_exit();
+  stack_smashing_abort();
+  return 0;
+}