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, 7 insertions, 4 deletions

diff --git a/sysdeps/x86/tst-cet-legacy-5.c b/sysdeps/x86/tst-cet-legacy-5.c
index e3efeb1f4e..d870de3eae 100644
--- a/sysdeps/x86/tst-cet-legacy-5.c
+++ b/sysdeps/x86/tst-cet-legacy-5.c
@@ -37,6 +37,12 @@ do_test_1 (const char *modname, bool fail)
   int (*fp) (void);
   void *h;
 
+  /* NB: dlopen should never fail on non-CET platforms.  If SHSTK is
+     disabled, assuming IBT is also disabled.  */
+  bool cet_enabled = _get_ssp () != 0 && !CET_MAYBE_DISABLED;
+  if (!cet_enabled)
+    fail = false;
+
   h = dlopen (modname, RTLD_LAZY);
   if (h == NULL)
     {
@@ -53,10 +59,7 @@ do_test_1 (const char *modname, bool fail)
       FAIL_EXIT1 ("cannot open '%s': %s\n", modname, err);
     }
 
-  /* NB: dlopen should never fail on non-CET platforms.  If SHSTK is
-     disabled, assuming IBT is also disabled.  */
-  bool cet_enabled = _get_ssp () != 0 && !CET_MAYBE_DISABLED;
-  if (fail && cet_enabled)
+  if (fail)
     FAIL_EXIT1 ("dlopen should have failed\n");
 
   fp = dlsym (h, "test");