V2 [PATCH] x86: Remove ARCH_CET_LEGACY_BITMAP [BZ #25397]

Message ID CAMe9rOoON6Dt-WaMmAQ3m76GMxp_RnKjLUZvL=QyheqCa_4=Vg@mail.gmail.com
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  • V2 [PATCH] x86: Remove ARCH_CET_LEGACY_BITMAP [BZ #25397]
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Commit Message

H.J. Lu March 9, 2020, 6:18 p.m.
On Mon, Mar 9, 2020 at 3:05 AM Florian Weimer <fw@deneb.enyo.de> wrote:
>

> * H. J. Lu:

>

> > diff --git a/sysdeps/x86/dl-cet.c b/sysdeps/x86/dl-cet.c

> > index ca3b5849bc..2be7a3a49f 100644

> > --- a/sysdeps/x86/dl-cet.c

> > +++ b/sysdeps/x86/dl-cet.c

>

> > +           /* IBT is enabled only if it is enabled in executable as

> > +              well as all shared objects.  */

> > +           enable_ibt &= (enable_ibt_type == CET_ALWAYS_ON

> > +                          || (l->l_cet & lc_ibt) != 0);

>

> As a general comment, I think we should add more logging as to way

> processes lose protection.  But that does not need to happen with this

> patch.

>

> > +               /* When IBT is enabled, we can't dlopening a shared

> > +                  object without IBT.  */

>

> “we cannot dlopen”


Fixed.

> > +               if (enable_ibt != ibt_enabled)

> > +                 _dl_signal_error (EINVAL, l->l_name, "dlopen",

> > +                                   N_("indirect branch tracking isn't enabled"));

>

> I think the error message should say *where* indirect branch tracking

> is not enabled.  I assume this is a property of the loaded object.


Fixed.   Now I got

.... libvirtd[1048]: internal error: Failed to load module
'/usr/lib64/libvirt/storage-backend/libvirt_storage_backend_rbd.so':
/usr/lib64/ceph/libceph-common.so.0: indirect branch tracking isn't
enabled: Invalid argument

>

> > +               /* When SHSTK is enabled, we can't dlopening a shared

> > +                  object without SHSTK.  */

> > +               if (enable_shstk != shstk_enabled)

> > +                 _dl_signal_error (EINVAL, l->l_name, "dlopen",

> > +                                   N_("shadow stack isn't enabled"));

>

> See above.


Also fixed.

> > diff --git a/sysdeps/x86/tst-cet-legacy-7.c b/sysdeps/x86/tst-cet-legacy-7.c

> > new file mode 100644

> > index 0000000000..e6f5d6f145

> > --- /dev/null

> > +++ b/sysdeps/x86/tst-cet-legacy-7.c

>

> > +  funcp = mmap (NULL, 0x1000, PROT_EXEC | PROT_READ | PROT_WRITE,

> > +             MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);

> > +  if (funcp == MAP_FAILED)

> > +    FAIL_EXIT1 ("mmap failed (errno=%d)", errno);

>

> You could use xmmap here.


Fixed,

> Rest of the patch looks okay to me.


Here is the updated patch.  OK for master?

Thanks.

--
H.J.

Comments

Florian Weimer March 10, 2020, 1:13 p.m. | #1
* H. J. Lu:

>> I think the error message should say *where* indirect branch tracking

>> is not enabled.  I assume this is a property of the loaded object.

>

> Fixed.   Now I got

>

> .... libvirtd[1048]: internal error: Failed to load module

> '/usr/lib64/libvirt/storage-backend/libvirt_storage_backend_rbd.so':

> /usr/lib64/ceph/libceph-common.so.0: indirect branch tracking isn't

> enabled: Invalid argument


What I meant is that the error message should say that the object
needs to be rebuilt with IBT/SHSTK support.  In the above, it's
unclear whether the process or the object has to enable IBT.

(The Invalid Argument part should also be suppressed.)

Patch

From 3fdfdca97bc103f633ff1f9ee7aa0a5bc9fa5748 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Tue, 25 Jun 2019 09:50:52 -0700
Subject: [PATCH] x86: Remove ARCH_CET_LEGACY_BITMAP [BZ #25397]

Since legacy bitmap doesn't cover jitted code generated by legacy JIT
engine, it isn't very useful.  This patch removes ARCH_CET_LEGACY_BITMAP
and treats indirect branch tracking similar to shadow stack by removing
legacy bitmap support.

	* sysdeps/unix/sysv/linux/x86/dl-cet.h
	(dl_cet_allocate_legacy_bitmap): Removed.
	* sysdeps/unix/sysv/linux/x86/include/asm/prctl.h
	(ARCH_CET_LEGACY_BITMAP): Removed.
	* sysdeps/x86/Makefile (tests): Add tst-cet-legacy-7.
	(CFLAGS-tst-cet-legacy-mod-5a.c): Changed to
	-fcf-protection=branch.
	(CFLAGS-tst-cet-legacy-mod-6a.c): Likewise.
	(CFLAGS-tst-cet-legacy-7.c): New.
	* sysdeps/x86/dl-cet.c (dl_cet_mark_legacy_region): Removed.
	(dl_cet_check): Remove legacy bitmap support.  Don't allow
	dlopening legacy shared library when IBT is enabled.  Set
	feature_1 if IBT or SHSTK is enabled in executable.
	* sysdeps/x86/dl-procruntime.c (_dl_x86_legacy_bitmap): Removed.
	* sysdeps/x86/tst-cet-legacy-4.c: Include <string.h> and
	<support/check.h>.
	(do_test): Check indirect branch tracking error.  Use
	FAIL_EXIT1.
	* sysdeps/x86/tst-cet-legacy-7.c: New file.
---
 sysdeps/unix/sysv/linux/x86/dl-cet.h          |  20 --
 .../unix/sysv/linux/x86/include/asm/prctl.h   |   5 -
 sysdeps/x86/Makefile                          |   7 +-
 sysdeps/x86/dl-cet.c                          | 217 +++++-------------
 sysdeps/x86/dl-procruntime.c                  |  11 -
 sysdeps/x86/tst-cet-legacy-4.c                |  19 +-
 sysdeps/x86/tst-cet-legacy-7.c                |  36 +++
 7 files changed, 109 insertions(+), 206 deletions(-)
 create mode 100644 sysdeps/x86/tst-cet-legacy-7.c

diff --git a/sysdeps/unix/sysv/linux/x86/dl-cet.h b/sysdeps/unix/sysv/linux/x86/dl-cet.h
index 9b2aaa238c..ae97a433a2 100644
--- a/sysdeps/unix/sysv/linux/x86/dl-cet.h
+++ b/sysdeps/unix/sysv/linux/x86/dl-cet.h
@@ -18,26 +18,6 @@ 
 #include <sys/prctl.h>
 #include <asm/prctl.h>
 
-static inline int __attribute__ ((always_inline))
-dl_cet_allocate_legacy_bitmap (unsigned long *legacy_bitmap)
-{
-  /* Allocate legacy bitmap.  */
-#ifdef __LP64__
-  return (int) INTERNAL_SYSCALL_CALL (arch_prctl,
-				      ARCH_CET_LEGACY_BITMAP, legacy_bitmap);
-#else
-  unsigned long long legacy_bitmap_u64[2];
-  int res = INTERNAL_SYSCALL_CALL (arch_prctl,
-				   ARCH_CET_LEGACY_BITMAP, legacy_bitmap_u64);
-  if (res == 0)
-    {
-      legacy_bitmap[0] = legacy_bitmap_u64[0];
-      legacy_bitmap[1] = legacy_bitmap_u64[1];
-    }
-  return res;
-#endif
-}
-
 static inline int __attribute__ ((always_inline))
 dl_cet_disable_cet (unsigned int cet_feature)
 {
diff --git a/sysdeps/unix/sysv/linux/x86/include/asm/prctl.h b/sysdeps/unix/sysv/linux/x86/include/asm/prctl.h
index f67f3299b9..45ad0b052f 100644
--- a/sysdeps/unix/sysv/linux/x86/include/asm/prctl.h
+++ b/sysdeps/unix/sysv/linux/x86/include/asm/prctl.h
@@ -24,9 +24,4 @@ 
      OUT: allocated shadow stack address: *addr.
  */
 # define ARCH_CET_ALLOC_SHSTK	0x3004
-/* Return legacy region bitmap info in unsigned long long *addr:
-     address: addr[0].
-     size: addr[1].
- */
-# define ARCH_CET_LEGACY_BITMAP	0x3005
 #endif /* ARCH_CET_STATUS */
diff --git a/sysdeps/x86/Makefile b/sysdeps/x86/Makefile
index 95182a508c..ec96b59a78 100644
--- a/sysdeps/x86/Makefile
+++ b/sysdeps/x86/Makefile
@@ -20,7 +20,7 @@  sysdep-dl-routines += dl-cet
 
 tests += tst-cet-legacy-1 tst-cet-legacy-1a tst-cet-legacy-2 \
 	 tst-cet-legacy-2a tst-cet-legacy-3 tst-cet-legacy-4 \
-	 tst-cet-legacy-5a tst-cet-legacy-6a
+	 tst-cet-legacy-5a tst-cet-legacy-6a tst-cet-legacy-7
 tst-cet-legacy-1a-ARGS = -- $(host-test-program-cmd)
 ifneq (no,$(have-tunables))
 tests += tst-cet-legacy-4a tst-cet-legacy-4b tst-cet-legacy-4c \
@@ -43,14 +43,15 @@  CFLAGS-tst-cet-legacy-4b.c += -fcf-protection
 CFLAGS-tst-cet-legacy-mod-4.c += -fcf-protection=none
 CFLAGS-tst-cet-legacy-5a.c += -fcf-protection
 CFLAGS-tst-cet-legacy-5b.c += -fcf-protection
-CFLAGS-tst-cet-legacy-mod-5a.c += -fcf-protection=none
+CFLAGS-tst-cet-legacy-mod-5a.c += -fcf-protection=branch
 CFLAGS-tst-cet-legacy-mod-5b.c += -fcf-protection
 CFLAGS-tst-cet-legacy-mod-5c.c += -fcf-protection
 CFLAGS-tst-cet-legacy-6a.c += -fcf-protection
 CFLAGS-tst-cet-legacy-6b.c += -fcf-protection
-CFLAGS-tst-cet-legacy-mod-6a.c += -fcf-protection=none
+CFLAGS-tst-cet-legacy-mod-6a.c += -fcf-protection=branch
 CFLAGS-tst-cet-legacy-mod-6b.c += -fcf-protection
 CFLAGS-tst-cet-legacy-mod-6c.c += -fcf-protection
+CFLAGS-tst-cet-legacy-7.c += -fcf-protection=none
 
 $(objpfx)tst-cet-legacy-1: $(objpfx)tst-cet-legacy-mod-1.so \
 		       $(objpfx)tst-cet-legacy-mod-2.so
diff --git a/sysdeps/x86/dl-cet.c b/sysdeps/x86/dl-cet.c
index ca3b5849bc..f527a1414c 100644
--- a/sysdeps/x86/dl-cet.c
+++ b/sysdeps/x86/dl-cet.c
@@ -33,63 +33,6 @@ 
 # error GNU_PROPERTY_X86_FEATURE_1_SHSTK != X86_FEATURE_1_SHSTK
 #endif
 
-static int
-dl_cet_mark_legacy_region (struct link_map *l)
-{
-  /* Mark PT_LOAD segments with PF_X in legacy code page bitmap.  */
-  size_t i, phnum = l->l_phnum;
-  const ElfW(Phdr) *phdr = l->l_phdr;
-#ifdef __x86_64__
-  typedef unsigned long long word_t;
-#else
-  typedef unsigned long word_t;
-#endif
-  unsigned int bits_to_set;
-  word_t mask_to_set;
-#define BITS_PER_WORD (sizeof (word_t) * 8)
-#define BITMAP_FIRST_WORD_MASK(start) \
-  (~((word_t) 0) << ((start) & (BITS_PER_WORD - 1)))
-#define BITMAP_LAST_WORD_MASK(nbits) \
-  (~((word_t) 0) >> (-(nbits) & (BITS_PER_WORD - 1)))
-
-  word_t *bitmap = (word_t *) GL(dl_x86_legacy_bitmap)[0];
-  word_t bitmap_size = GL(dl_x86_legacy_bitmap)[1];
-  word_t *p;
-  size_t page_size = GLRO(dl_pagesize);
-
-  for (i = 0; i < phnum; i++)
-    if (phdr[i].p_type == PT_LOAD && (phdr[i].p_flags & PF_X))
-      {
-	/* One bit in legacy bitmap represents a page.  */
-	ElfW(Addr) start = (phdr[i].p_vaddr + l->l_addr) / page_size;
-	ElfW(Addr) len = (phdr[i].p_memsz + page_size - 1) / page_size;
-	ElfW(Addr) end = start + len;
-
-	if ((end / 8) > bitmap_size)
-	  return -EINVAL;
-
-	p = bitmap + (start / BITS_PER_WORD);
-	bits_to_set = BITS_PER_WORD - (start % BITS_PER_WORD);
-	mask_to_set = BITMAP_FIRST_WORD_MASK (start);
-
-	while (len >= bits_to_set)
-	  {
-	    *p |= mask_to_set;
-	    len -= bits_to_set;
-	    bits_to_set = BITS_PER_WORD;
-	    mask_to_set = ~((word_t) 0);
-	    p++;
-	  }
-	if (len)
-	  {
-	    mask_to_set &= BITMAP_LAST_WORD_MASK (end);
-	    *p |= mask_to_set;
-	  }
-      }
-
-  return 0;
-}
-
 /* Check if object M is compatible with CET.  */
 
 static void
@@ -117,6 +60,8 @@  dl_cet_check (struct link_map *m, const char *program)
   if (ibt_enabled || shstk_enabled)
     {
       struct link_map *l = NULL;
+      unsigned int ibt_legacy = 0, shstk_legacy = 0;
+      bool found_ibt_legacy = false, found_shstk_legacy = false;
 
       /* Check if IBT and SHSTK are enabled in object.  */
       bool enable_ibt = (ibt_enabled
@@ -142,10 +87,7 @@  dl_cet_check (struct link_map *m, const char *program)
 	 support IBT nor SHSTK.  */
       if (enable_ibt || enable_shstk)
 	{
-	  int res;
 	  unsigned int i;
-	  unsigned int first_legacy, last_legacy;
-	  bool need_legacy_bitmap = false;
 
 	  i = m->l_searchlist.r_nlist;
 	  while (i-- > 0)
@@ -167,91 +109,25 @@  dl_cet_check (struct link_map *m, const char *program)
 		continue;
 #endif
 
-	      if (enable_ibt
-		  && enable_ibt_type != CET_ALWAYS_ON
-		  && !(l->l_cet & lc_ibt))
+	      /* IBT is enabled only if it is enabled in executable as
+		 well as all shared objects.  */
+	      enable_ibt &= (enable_ibt_type == CET_ALWAYS_ON
+			     || (l->l_cet & lc_ibt) != 0);
+	      if (!found_ibt_legacy && enable_ibt != ibt_enabled)
 		{
-		  /* Remember the first and last legacy objects.  */
-		  if (!need_legacy_bitmap)
-		    last_legacy = i;
-		  first_legacy = i;
-		  need_legacy_bitmap = true;
+		  found_ibt_legacy = true;
+		  ibt_legacy = i;
 		}
 
 	      /* SHSTK is enabled only if it is enabled in executable as
 		 well as all shared objects.  */
 	      enable_shstk &= (enable_shstk_type == CET_ALWAYS_ON
 			       || (l->l_cet & lc_shstk) != 0);
-	    }
-
-	  if (need_legacy_bitmap)
-	    {
-	      if (GL(dl_x86_legacy_bitmap)[0])
-		{
-		  /* Change legacy bitmap to writable.  */
-		  if (__mprotect ((void *) GL(dl_x86_legacy_bitmap)[0],
-				  GL(dl_x86_legacy_bitmap)[1],
-				  PROT_READ | PROT_WRITE) < 0)
-		    {
-mprotect_failure:
-		      if (program)
-			_dl_fatal_printf ("%s: mprotect legacy bitmap failed\n",
-					  l->l_name);
-		      else
-			_dl_signal_error (EINVAL, l->l_name, "dlopen",
-					  N_("mprotect legacy bitmap failed"));
-		    }
-		}
-	      else
+	      if (enable_shstk != shstk_enabled)
 		{
-		  /* Allocate legacy bitmap.  */
-		  int res = dl_cet_allocate_legacy_bitmap
-		    (GL(dl_x86_legacy_bitmap));
-		  if (res != 0)
-		    {
-		      if (program)
-			_dl_fatal_printf ("%s: legacy bitmap isn't available\n",
-					  l->l_name);
-		      else
-			_dl_signal_error (EINVAL, l->l_name, "dlopen",
-					  N_("legacy bitmap isn't available"));
-		    }
+		  found_shstk_legacy = true;
+		  shstk_legacy = i;
 		}
-
-	      /* Put legacy shared objects in legacy bitmap.  */
-	      for (i = first_legacy; i <= last_legacy; i++)
-		{
-		  l = m->l_initfini[i];
-
-		  if (l->l_init_called || (l->l_cet & lc_ibt))
-		    continue;
-
-#ifdef SHARED
-		  if (l == &GL(dl_rtld_map)
-		      ||  l->l_real == &GL(dl_rtld_map)
-		      || (program && l == m))
-		    continue;
-#endif
-
-		  /* If IBT is enabled in executable and IBT isn't enabled
-		     in this shard object, mark PT_LOAD segments with PF_X
-		     in legacy code page bitmap.  */
-		  res = dl_cet_mark_legacy_region (l);
-		  if (res != 0)
-		    {
-		      if (program)
-			_dl_fatal_printf ("%s: failed to mark legacy code region\n",
-					  l->l_name);
-		      else
-			_dl_signal_error (-res, l->l_name, "dlopen",
-					  N_("failed to mark legacy code region"));
-		    }
-		}
-
-	      /* Change legacy bitmap to read-only.  */
-	      if (__mprotect ((void *) GL(dl_x86_legacy_bitmap)[0],
-			      GL(dl_x86_legacy_bitmap)[1], PROT_READ) < 0)
-		goto mprotect_failure;
 	    }
 	}
 
@@ -259,23 +135,40 @@  mprotect_failure:
 
       if (enable_ibt != ibt_enabled || enable_shstk != shstk_enabled)
 	{
-	  if (!program
-	      && enable_shstk_type != CET_PERMISSIVE)
+	  if (!program)
 	    {
-	      /* When SHSTK is enabled, we can't dlopening a shared
-		 object without SHSTK.  */
-	      if (enable_shstk != shstk_enabled)
-		_dl_signal_error (EINVAL, l->l_name, "dlopen",
-				  N_("shadow stack isn't enabled"));
-	      return;
+	      if (enable_ibt_type != CET_PERMISSIVE)
+		{
+		  /* When IBT is enabled, we cannot dlopen a shared
+		     object without IBT.  */
+		  if (found_ibt_legacy)
+		    _dl_signal_error (EINVAL,
+				      m->l_initfini[ibt_legacy]->l_name,
+				      "dlopen",
+				      N_("indirect branch tracking isn't enabled"));
+		}
+
+	      if (enable_shstk_type != CET_PERMISSIVE)
+		{
+		  /* When SHSTK is enabled, we cannot dlopen a shared
+		     object without SHSTK.  */
+		  if (found_shstk_legacy)
+		    _dl_signal_error (EINVAL,
+				      m->l_initfini[shstk_legacy]->l_name,
+				      "dlopen",
+				      N_("shadow stack isn't enabled"));
+		}
+
+	      if (enable_ibt_type != CET_PERMISSIVE
+		  && enable_shstk_type != CET_PERMISSIVE)
+		return;
 	    }
 
 	  /* Disable IBT and/or SHSTK if they are enabled by kernel, but
 	     disabled in executable or shared objects.  */
 	  unsigned int cet_feature = 0;
 
-	  /* Disable IBT only during program startup.  */
-	  if (program && !enable_ibt)
+	  if (!enable_ibt)
 	    cet_feature |= GNU_PROPERTY_X86_FEATURE_1_IBT;
 	  if (!enable_shstk)
 	    cet_feature |= GNU_PROPERTY_X86_FEATURE_1_SHSTK;
@@ -286,8 +179,14 @@  mprotect_failure:
 	      if (program)
 		_dl_fatal_printf ("%s: can't disable CET\n", program);
 	      else
-		_dl_signal_error (-res, l->l_name, "dlopen",
-				  N_("can't disable CET"));
+		{
+		  if (found_ibt_legacy)
+		    l = m->l_initfini[ibt_legacy];
+		  else
+		    l = m->l_initfini[shstk_legacy];
+		  _dl_signal_error (-res, l->l_name, "dlopen",
+				    N_("can't disable CET"));
+		}
 	    }
 
 	  /* Clear the disabled bits in dl_x86_feature_1.  */
@@ -297,17 +196,21 @@  mprotect_failure:
 	}
 
 #ifdef SHARED
-      if (program
-	  && (!shstk_enabled
-	      || enable_shstk_type != CET_PERMISSIVE)
-	  && (ibt_enabled || shstk_enabled))
+      if (program && (ibt_enabled || shstk_enabled))
 	{
-	  /* Lock CET if IBT or SHSTK is enabled in executable.  Don't
-	     lock CET if SHSTK is enabled permissively.  */
-	  int res = dl_cet_lock_cet ();
-	  if (res != 0)
-	    _dl_fatal_printf ("%s: can't lock CET\n", program);
+	  if ((!ibt_enabled
+	       || enable_ibt_type != CET_PERMISSIVE)
+	      && (!shstk_enabled
+		  || enable_shstk_type != CET_PERMISSIVE))
+	    {
+	      /* Lock CET if IBT or SHSTK is enabled in executable unless
+	         IBT or SHSTK is enabled permissively.  */
+	      int res = dl_cet_lock_cet ();
+	      if (res != 0)
+		_dl_fatal_printf ("%s: can't lock CET\n", program);
+	    }
 
+	  /* Set feature_1 if IBT or SHSTK is enabled in executable.  */
 	  cet_feature_changed = true;
 	}
 #endif
diff --git a/sysdeps/x86/dl-procruntime.c b/sysdeps/x86/dl-procruntime.c
index fb36801f3e..5e39a38133 100644
--- a/sysdeps/x86/dl-procruntime.c
+++ b/sysdeps/x86/dl-procruntime.c
@@ -54,15 +54,4 @@  PROCINFO_CLASS unsigned int _dl_x86_feature_1[2]
 # else
 ,
 # endif
-
-# if !defined PROCINFO_DECL && defined SHARED
-  ._dl_x86_legacy_bitmap
-# else
-PROCINFO_CLASS unsigned long _dl_x86_legacy_bitmap[2]
-# endif
-# if !defined SHARED || defined PROCINFO_DECL
-;
-# else
-,
-# endif
 #endif
diff --git a/sysdeps/x86/tst-cet-legacy-4.c b/sysdeps/x86/tst-cet-legacy-4.c
index a77078afc9..da1f3d1e0d 100644
--- a/sysdeps/x86/tst-cet-legacy-4.c
+++ b/sysdeps/x86/tst-cet-legacy-4.c
@@ -20,6 +20,9 @@ 
 #include <dlfcn.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
+
+#include <support/check.h>
 
 static int
 do_test (void)
@@ -31,22 +34,18 @@  do_test (void)
   h = dlopen (modname, RTLD_LAZY);
   if (h == NULL)
     {
-      printf ("cannot open '%s': %s\n", modname, dlerror ());
-      exit (1);
+      const char *err = dlerror ();
+      if (!strstr (err, "indirect branch tracking isn't enabled"))
+	FAIL_EXIT1 ("incorrect dlopen '%s' error: %s\n", modname, err);
+      return 0;
     }
 
   fp = dlsym (h, "test");
   if (fp == NULL)
-    {
-      printf ("cannot get symbol 'test': %s\n", dlerror ());
-      exit (1);
-    }
+    FAIL_EXIT1 ("cannot get symbol 'test': %s\n", dlerror ());
 
   if (fp () != 0)
-    {
-      puts ("test () != 0");
-      exit (1);
-    }
+    FAIL_EXIT1 ("test () != 0");
 
   dlclose (h);
 
diff --git a/sysdeps/x86/tst-cet-legacy-7.c b/sysdeps/x86/tst-cet-legacy-7.c
new file mode 100644
index 0000000000..cf4c2779ce
--- /dev/null
+++ b/sysdeps/x86/tst-cet-legacy-7.c
@@ -0,0 +1,36 @@ 
+/* Check compatibility of legacy executable with a JIT engine.
+   Copyright (C) 2020 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 <stdio.h>
+#include <sys/mman.h>
+#include <support/xunistd.h>
+
+static int
+do_test (void)
+{
+  void (*funcp) (void);
+  funcp = xmmap (NULL, 0x1000, PROT_EXEC | PROT_READ | PROT_WRITE,
+		 MAP_ANONYMOUS | MAP_PRIVATE, -1);
+  printf ("mmap = %p\n", funcp);
+  /* Write RET instruction.  */
+  *(char *) funcp = 0xc3;
+  funcp ();
+  return 0;
+}
+
+#include <support/test-driver.c>
-- 
2.24.1