[glibc] x86/cet: Don't disable CET if not single threaded

[H.J. Lu <hjl@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=41560a9312ce0ec7203480eef8f865076bff9edb

commit 41560a9312ce0ec7203480eef8f865076bff9edb
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Fri Jul 28 14:06:01 2023 -0700

    x86/cet: Don't disable CET if not single threaded
    
    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.

Diff:
---
 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 67c51ee8c2..e486e549be 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.
@@ -233,7 +234,10 @@ 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");
@@ -249,7 +253,10 @@ 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");