x86-64: Align child stack to 16 bytes [BZ #27902]

In the x86-64 clone wrapper, align child stack to 16 bytes per the
x86-64 psABI.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

sysdeps/unix/sysv/linux/Makefile

@@ -109,7 +109,7 @@ tests += tst-clone tst-clone2 tst-clone3 tst-fanotify tst-personality \
 	 tst-tgkill tst-sysvsem-linux tst-sysvmsg-linux tst-sysvshm-linux \
 	 tst-timerfd tst-ppoll \
 	 tst-clock_adjtime tst-adjtimex tst-ntp_adjtime tst-ntp_gettime \
-	 tst-ntp_gettimex tst-sigtimedwait
+	 tst-ntp_gettimex tst-sigtimedwait tst-misalign-clone
 
 # Test for the symbol version of fcntl that was replaced in glibc 2.28.
 ifeq ($(have-GLIBC_2.27)$(build-shared),yesyes)

sysdeps/unix/sysv/linux/tst-misalign-clone.c

@@ -0,0 +1,96 @@
+/* Verify that the clone wrapper properly aligns the child stack.
+   Copyright (C) 2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <sched.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include <libc-pointer-arith.h>
+#include <tst-stack-align.h>
+#include <stackinfo.h>
+#include <support/xunistd.h>
+#include <support/check.h>
+
+static int
+check_stack_alignment (void *arg)
+{
+  bool ok = true;
+
+  puts ("in f");
+
+  if (TEST_STACK_ALIGN ())
+    ok = false;
+
+  return ok ? 0 : 1;
+}
+
+static int
+do_test (void)
+{
+  puts ("in do_test");
+
+  if (TEST_STACK_ALIGN ())
+    FAIL_EXIT1 ("stack isn't aligned\n");
+
+#ifdef __ia64__
+# define STACK_SIZE (256 * 1024)
+#else
+# define STACK_SIZE (128 * 1024)
+#endif
+
+  char st[STACK_SIZE + 1];
+  /* NB: Align child stack to 1 byte.  */
+  char *stack = PTR_ALIGN_UP (&st[0], 2) + 1;
+
+#ifdef __ia64__
+  extern int __clone2 (int (*__fn) (void *__arg), void *__child_stack_base,
+		       size_t __child_stack_size, int __flags,
+		       void *__arg, ...);
+  pid_t p = __clone2 (check_stack_alignment, stack, STACK_SIZE, 0, 0);
+#else
+# if _STACK_GROWS_DOWN
+  pid_t p = clone (check_stack_alignment, stack + STACK_SIZE, 0, 0);
+# elif _STACK_GROWS_UP
+  pid_t p = clone (check_stack_alignment, stack, 0, 0);
+# else
+#  error "Define either _STACK_GROWS_DOWN or _STACK_GROWS_UP"
+# endif
+#endif
+
+  /* Clone must not fail.  */
+  TEST_VERIFY_EXIT (p != -1);
+
+  int e;
+  xwaitpid (p, &e, __WCLONE);
+  if (!WIFEXITED (e))
+    {
+      if (WIFSIGNALED (e))
+	printf ("died from signal %s\n", strsignal (WTERMSIG (e)));
+     FAIL_EXIT1 ("process did not terminate correctly");
+    }
+
+  if (WEXITSTATUS (e) != 0)
+    FAIL_EXIT1 ("exit code %d", WEXITSTATUS (e));
+
+  return 0;
+}
+
+#include <support/test-driver.c>

sysdeps/unix/sysv/linux/x86_64/clone.S

@@ -54,12 +54,15 @@ ENTRY (__clone)
 	movq	$-EINVAL,%rax
 	testq	%rdi,%rdi		/* no NULL function pointers */
 	jz	SYSCALL_ERROR_LABEL
-	testq	%rsi,%rsi		/* no NULL stack pointers */
+
-	jz	SYSCALL_ERROR_LABEL
+	/* Align stack to 16 bytes per the x86-64 psABI.  */
+	andq	$-16, %rsi
+	jz	SYSCALL_ERROR_LABEL	/* no NULL stack pointers */
 
 	/* Insert the argument onto the new stack.  */
+	movq	%rcx,-8(%rsi)
+
 	subq	$16,%rsi
-	movq	%rcx,8(%rsi)
 
 	/* Save the function pointer.  It will be popped off in the
 	   child.  */