[PATCH] i386: In makecontext, align the stack before calling exit [BZ #22667]

[fweimer at redhat dot com (Florian Weimer)]

Before this change, if glibc was compiled with SSE instructions and a
sufficiently recent GCC, an unaligned stack access in
__run_exit_handlers would cause stdlib/tst-makecontext to crash.

2018-01-04  Florian Weimer  <fweimer@redhat.com>

	[BZ #22667]
	* sysdeps/unix/sysv/linux/i386/makecontext.S (__makecontext):
	Align the stack before calling exit.
	* stdlib/tst-makecontext-align.c: New file.
	* stdlib/Makefile (tests): Add tst-makecontext-align.

diff --git a/stdlib/Makefile b/stdlib/Makefile
index 691325b91b..7c363a6e4d 100644
--- a/stdlib/Makefile
+++ b/stdlib/Makefile
@@ -83,7 +83,8 @@ tests		:= tst-strtol tst-strtod testmb testrand testsort testdiv   \
 		   tst-getrandom tst-atexit tst-at_quick_exit 		    \
 		   tst-cxa_atexit tst-on_exit test-atexit-race 		    \
 		   test-at_quick_exit-race test-cxa_atexit-race             \
-		   test-on_exit-race test-dlclose-exit-race
+		   test-on_exit-race test-dlclose-exit-race 		    \
+		   tst-makecontext-align
 
 tests-internal	:= tst-strtod1i tst-strtod3 tst-strtod4 tst-strtod5i \
 		   tst-tls-atexit tst-tls-atexit-nodelete
diff --git a/stdlib/tst-makecontext-align.c b/stdlib/tst-makecontext-align.c
new file mode 100644
index 0000000000..82394b4f6b
--- /dev/null
+++ b/stdlib/tst-makecontext-align.c
@@ -0,0 +1,241 @@
+/* Check stack alignment provided by makecontext.
+   Copyright (C) 2018 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
+   <http://www.gnu.org/licenses/>.  */
+
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <support/check.h>
+#include <support/namespace.h>
+#include <support/xunistd.h>
+#include <sys/mman.h>
+#include <ucontext.h>
+
+/* Used for error reporting.  */
+static const char *context;
+
+/* Check that ADDRESS is aligned to ALIGNMENT bytes, behind a compiler
+   barrier.  */
+__attribute__ ((noinline, noclone, weak))
+void
+check_align (void *address, size_t alignment)
+{
+  uintptr_t uaddress = (uintptr_t) address;
+  if ((uaddress % alignment) != 0)
+    {
+      support_record_failure ();
+      printf ("error: %s: object at address %p is not aligned to %zu bytes\n",
+              context, address, alignment);
+    }
+}
+
+/* Various alignment checking functions.  */
+
+__attribute__ ((noinline, noclone, weak))
+void
+check_align_int (void)
+{
+  int a;
+  check_align (&a, __alignof__ (a));
+}
+
+__attribute__ ((noinline, noclone, weak))
+void
+check_align_long (void)
+{
+  long a;
+  check_align (&a, __alignof__ (a));
+}
+
+__attribute__ ((noinline, noclone, weak))
+void
+check_align_long_long (void)
+{
+  long long a;
+  check_align (&a, __alignof__ (a));
+}
+
+__attribute__ ((noinline, noclone, weak))
+void
+check_align_double (void)
+{
+  double a;
+  check_align (&a, __alignof__ (a));
+}
+
+__attribute__ ((noinline, noclone, weak))
+void
+check_align_4 (void)
+{
+  int a __attribute__ ((aligned (4)));
+  check_align (&a, 4);
+}
+
+__attribute__ ((noinline, noclone, weak))
+void
+check_align_8 (void)
+{
+  double a __attribute__ ((aligned (8)));
+  check_align (&a, 8);
+}
+
+__attribute__ ((noinline, noclone, weak))
+void
+check_align_16 (void)
+{
+  struct aligned
+  {
+    double x0  __attribute__ ((aligned (16)));
+    double x1;
+  } a;
+  check_align (&a, 16);
+}
+
+__attribute__ ((noinline, noclone, weak))
+void
+check_align_32 (void)
+{
+  struct aligned
+  {
+    double x0  __attribute__ ((aligned (32)));
+    double x1;
+    double x2;
+    double x3;
+  } a;
+  check_align (&a, 32);
+}
+
+/* Call all the alignment checking functions.  */
+__attribute__ ((noinline, noclone, weak))
+void
+check_alignments (void)
+{
+  check_align_int ();
+  check_align_long ();
+  check_align_long_long ();
+  check_align_double ();
+  check_align_4 ();
+  check_align_8 ();
+  check_align_16 ();
+  check_align_32 ();
+}
+
+/* Callback functions for makecontext and their invokers (to be used
+   with support_isolate_in_subprocess).  */
+
+static ucontext_t ucp;
+
+static void
+callback_0 (void)
+{
+  context = "callback_0";
+  check_alignments ();
+  context = "after return from callback_0";
+}
+
+static void
+invoke_callback_0 (void *closure)
+{
+  makecontext (&ucp, (void *) callback_0, 0);
+  if (setcontext (&ucp) != 0)
+    FAIL_EXIT1 ("setcontext");
+  FAIL_EXIT1 ("setcontext returned");
+}
+
+static void
+callback_1 (int arg1)
+{
+  context = "callback_1";
+  check_alignments ();
+  TEST_COMPARE (arg1, 101);
+  context = "after return from callback_1";
+}
+
+static void
+invoke_callback_1 (void *closure)
+{
+  makecontext (&ucp, (void *) callback_1, 1, 101);
+  if (setcontext (&ucp) != 0)
+    FAIL_EXIT1 ("setcontext");
+  FAIL_EXIT1 ("setcontext returned");
+}
+
+static void
+callback_2 (int arg1, int arg2)
+{
+  context = "callback_2";
+  check_alignments ();
+  TEST_COMPARE (arg1, 201);
+  TEST_COMPARE (arg2, 202);
+  context = "after return from callback_2";
+}
+
+static void
+invoke_callback_2 (void *closure)
+{
+  makecontext (&ucp, (void *) callback_2, 2, 201, 202);
+  if (setcontext (&ucp) != 0)
+    FAIL_EXIT1 ("setcontext");
+  FAIL_EXIT1 ("setcontext returned");
+}
+
+static void
+callback_3 (int arg1, int arg2, int arg3)
+{
+  context = "callback_3";
+  check_alignments ();
+  TEST_COMPARE (arg1, 301);
+  TEST_COMPARE (arg2, 302);
+  TEST_COMPARE (arg3, 303);
+  context = "after return from callback_3";
+}
+
+static void
+invoke_callback_3 (void *closure)
+{
+  makecontext (&ucp, (void *) callback_3, 3, 301, 302, 303);
+  if (setcontext (&ucp) != 0)
+    FAIL_EXIT1 ("setcontext");
+  FAIL_EXIT1 ("setcontext returned");
+}
+
+static int
+do_test (void)
+{
+  context = "direct call";
+  check_alignments ();
+
+  atexit (check_alignments);
+
+  if (getcontext (&ucp) != 0)
+    FAIL_UNSUPPORTED ("getcontext");
+
+  ucp.uc_link = NULL;
+  ucp.uc_stack.ss_size = 512 * 1024;
+  ucp.uc_stack.ss_sp = xmmap (NULL, ucp.uc_stack.ss_size,
+                              PROT_READ | PROT_WRITE,
+                              MAP_PRIVATE | MAP_ANONYMOUS, -1);
+
+  support_isolate_in_subprocess (invoke_callback_0, NULL);
+  support_isolate_in_subprocess (invoke_callback_1, NULL);
+  support_isolate_in_subprocess (invoke_callback_2, NULL);
+  support_isolate_in_subprocess (invoke_callback_3, NULL);
+
+  return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/sysdeps/unix/sysv/linux/i386/makecontext.S b/sysdeps/unix/sysv/linux/i386/makecontext.S
index efa4955033..e3ca3dc0d5 100644
--- a/sysdeps/unix/sysv/linux/i386/makecontext.S
+++ b/sysdeps/unix/sysv/linux/i386/makecontext.S
@@ -108,9 +108,19 @@ L(exitcode):
 	call	HIDDEN_JUMPTARGET(__setcontext)
 	/* If this returns (which can happen if the syscall fails) we'll
 	   exit the program with the return error value (-1).  */
+	jmp L(call_exit)
 
-	movl	%eax, (%esp)
-2:	call	HIDDEN_JUMPTARGET(exit)
+2:
+	/* Exit with status 0.  */
+	xorl	%eax, %eax
+
+L(call_exit):
+	/* Align the stack and pass the exit code (from %eax).  */
+	andl	$0xfffffff0, %esp
+	subl	$12, %esp
+	pushl	%eax
+
+	call	HIDDEN_JUMPTARGET(exit)
 	/* The 'exit' call should never return.  In case it does cause
 	   the process to terminate.  */
 	hlt