x86: Properly set usable CET feature bits [BZ #26625]

commit 94cd37ebb293321115a36a422b091fdb72d2fb08
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Wed Sep 16 05:27:32 2020 -0700

    x86: Use HAS_CPU_FEATURE with IBT and SHSTK [BZ #26625]

broke

GLIBC_TUNABLES=glibc.cpu.hwcaps=-IBT,-SHSTK

since it can no longer disable IBT nor SHSTK.  Handle IBT and SHSTK with:

1. Revert commit 94cd37ebb293321115a36a422b091fdb72d2fb08.
2. Clears the usable CET feature bits if kernel doesn't support CET.
3. Add GLIBC_TUNABLES tests without dlopen.
4. Add tests to verify that CPU_FEATURE_USABLE on IBT and SHSTK matches
_get_ssp.
5. Update GLIBC_TUNABLES tests with dlopen to verify that CET is disabled
with GLIBC_TUNABLES.

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

1 files changed, 43 insertions, 0 deletions

diff --git a/sysdeps/x86/tst-cet-legacy-10.c b/sysdeps/x86/tst-cet-legacy-10.c
new file mode 100644
index 0000000000..a618557f45
--- /dev/null
+++ b/sysdeps/x86/tst-cet-legacy-10.c
@@ -0,0 +1,43 @@
+/* Check CPU_FEATURE_USABLE on IBT and SHSTK.
+   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 <x86intrin.h>
+#include <sys/platform/x86.h>
+#include <support/test-driver.h>
+#include <support/xunistd.h>
+
+/* Check that CPU_FEATURE_USABLE on IBT and SHSTK matches _get_ssp.  */
+
+static int
+do_test (void)
+{
+  if (_get_ssp () != 0)
+    {
+      if (CPU_FEATURE_USABLE (IBT) && CPU_FEATURE_USABLE (SHSTK))
+	return EXIT_SUCCESS;
+    }
+  else
+    {
+      if (!CPU_FEATURE_USABLE (IBT) && !CPU_FEATURE_USABLE (SHSTK))
+	return EXIT_SUCCESS;
+    }
+
+  return EXIT_FAILURE;
+}
+
+#include <support/test-driver.c>