x86/CET: Add a setcontext test for CET

Verify that setcontext works with gaps above and below the newly
allocated shadow stack.

	* sysdeps/unix/sysv/linux/x86/Makefile (tests): Add
	tst-cet-setcontext-1 if CET is enabled.
	(CFLAGS-tst-cet-setcontext-1.c): Add -mshstk.
	* sysdeps/unix/sysv/linux/x86/tst-cet-setcontext-1.c: New file.

2 files changed, 134 insertions, 0 deletions

diff --git a/sysdeps/unix/sysv/linux/x86/Makefile b/sysdeps/unix/sysv/linux/x86/Makefile
index 111ff9f..a30fdb1 100644
--- a/sysdeps/unix/sysv/linux/x86/Makefile
+++ b/sysdeps/unix/sysv/linux/x86/Makefile
@@ -23,3 +23,10 @@ endif
 ifeq ($(subdir),setjmp)
 tests += tst-saved_mask-1
 endif
+
+ifeq ($(enable-cet),yes)
+ifeq ($(subdir),stdlib)
+tests += tst-cet-setcontext-1
+CFLAGS-tst-cet-setcontext-1.c += -mshstk
+endif
+endif
diff --git a/sysdeps/unix/sysv/linux/x86/tst-cet-setcontext-1.c b/sysdeps/unix/sysv/linux/x86/tst-cet-setcontext-1.c
new file mode 100644
index 0000000..ecf86a9
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/x86/tst-cet-setcontext-1.c
@@ -0,0 +1,127 @@
+/* Check getcontext and setcontext on the context from makecontext
+   with shadow stack.
+   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 <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <ucontext.h>
+#include <unistd.h>
+#include <sys/mman.h>
+#include <stdatomic.h>
+#include <x86intrin.h>
+
+static ucontext_t ctx[5];
+static atomic_int done;
+
+static void
+__attribute__((noinline, noclone))
+f2 (void)
+{
+  printf ("start f2\n");
+  done++;
+  if (setcontext (&ctx[2]) != 0)
+    {
+      printf ("%s: setcontext: %m\n", __FUNCTION__);
+      exit (EXIT_FAILURE);
+    }
+}
+
+static void
+f1 (void)
+{
+  printf ("start f1\n");
+  if (getcontext (&ctx[2]) != 0)
+    {
+      printf ("%s: getcontext: %m\n", __FUNCTION__);
+      exit (EXIT_FAILURE);
+    }
+  if (done)
+    exit (EXIT_SUCCESS);
+  f2 ();
+}
+
+static int
+do_test (void)
+{
+  char st1[32768];
+  puts ("making contexts");
+  if (getcontext (&ctx[0]) != 0)
+    {
+      printf ("%s: getcontext: %m\n", __FUNCTION__);
+      exit (EXIT_FAILURE);
+    }
+  if (getcontext (&ctx[1]) != 0)
+    {
+      printf ("%s: getcontext: %m\n", __FUNCTION__);
+      exit (EXIT_FAILURE);
+    }
+
+  ctx[3].uc_stack.ss_sp = st1;
+  ctx[3].uc_stack.ss_size = sizeof st1;
+  ctx[3].uc_link = &ctx[0];
+  makecontext (&ctx[3], (void (*) (void)) f1, 0);
+
+  ctx[1].uc_stack.ss_sp = st1;
+  ctx[1].uc_stack.ss_size = sizeof st1;
+  ctx[1].uc_link = &ctx[0];
+  makecontext (&ctx[1], (void (*) (void)) f1, 0);
+
+  ctx[4].uc_stack.ss_sp = st1;
+  ctx[4].uc_stack.ss_size = sizeof st1;
+  ctx[4].uc_link = &ctx[0];
+  makecontext (&ctx[4], (void (*) (void)) f1, 0);
+
+  /* NB: When shadow stack is enabled, makecontext calls arch_prctl
+     with ARCH_CET_ALLOC_SHSTK to allocate a new shadow stack which
+     can be unmapped.  The base address and size of the new shadow
+     stack are returned in __ssp[1] and __ssp[2].  makecontext is
+     called for CTX1, CTX3 and CTX4.  But only CTX1 is used.  New
+     shadow stacks are allocated in the order of CTX3, CTX1, CTX4.
+     It is very likely that CTX1's shadow stack is placed between
+     CTX3 and CTX4.  We munmap CTX3's and CTX4's shadow stacks to
+     create gaps above and below CTX1's shadow stack.  We check
+     that setcontext CTX1 works correctly in this case.  */
+  if (_get_ssp () != 0)
+    {
+      if (ctx[3].__ssp[1] != 0
+	  && munmap ((void *) (uintptr_t) ctx[3].__ssp[1],
+		     (size_t) ctx[3].__ssp[2]) != 0)
+	{
+	  printf ("%s: munmap: %m\n", __FUNCTION__);
+	  exit (EXIT_FAILURE);
+	}
+
+      if (ctx[4].__ssp[1] != 0
+	  && munmap ((void *) (uintptr_t) ctx[4].__ssp[1],
+		     (size_t) ctx[4].__ssp[2]) != 0)
+	{
+	  printf ("%s: munmap: %m\n", __FUNCTION__);
+	  exit (EXIT_FAILURE);
+	}
+    }
+
+  if (setcontext (&ctx[1]) != 0)
+    {
+      printf ("%s: setcontext: %m\n", __FUNCTION__);
+      exit (EXIT_FAILURE);
+    }
+  exit (EXIT_FAILURE);
+}
+
+#include <support/test-driver.c>