[PATCH v3 7/9] x86/cet: Don't disable CET if not single threaded

[H.J. Lu]

In permissive mode, don't disable IBT nor SHSTK when dlopening a legacy
shared library if not single threaded since IBT and SHSTK may be still
enabled in other threads.  Other threads with IBT or SHSTK enabled will
crash when calling functions in the legacy shared library.  Instead, an
error will be issued.
---
 sysdeps/x86/dl-cet.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/sysdeps/x86/dl-cet.c b/sysdeps/x86/dl-cet.c
index f40f8e17b0..25add215f2 100644
--- a/sysdeps/x86/dl-cet.c
+++ b/sysdeps/x86/dl-cet.c
@@ -20,6 +20,7 @@
 #include <libintl.h>
 #include <ldsodefs.h>
 #include <dl-cet.h>
+#include <sys/single_threaded.h>
 
 /* GNU_PROPERTY_X86_FEATURE_1_IBT and GNU_PROPERTY_X86_FEATURE_1_SHSTK
    are defined in <elf.h>, which are only available for C sources.
@@ -204,7 +205,10 @@ dl_cet_check_dlopen (struct link_map *m, struct dl_cet_info *info)
       && (info->feature_1_legacy
 	  & GNU_PROPERTY_X86_FEATURE_1_IBT) != 0)
     {
-      if (info->enable_ibt_type != cet_permissive)
+      /* Don't disable IBT if not single threaded since IBT may be still
+	 enabled in other threads.  */
+      if (info->enable_ibt_type != cet_permissive
+	  || !SINGLE_THREAD_P)
 	{
 	  legacy_obj = info->feature_1_legacy_ibt;
 	  msg = N_("rebuild shared object with IBT support enabled");
@@ -220,7 +224,10 @@ dl_cet_check_dlopen (struct link_map *m, struct dl_cet_info *info)
       && (info->feature_1_legacy
 	  & GNU_PROPERTY_X86_FEATURE_1_SHSTK) != 0)
     {
-      if (info->enable_shstk_type != cet_permissive)
+      /* Don't disable SHSTK if not single threaded since SHSTK may be
+         still enabled in other threads.  */
+      if (info->enable_shstk_type != cet_permissive
+	  || !SINGLE_THREAD_P)
 	{
 	  legacy_obj = info->feature_1_legacy_shstk;
 	  msg = N_("rebuild shared object with SHSTK support enabled");
-- 
2.43.0