diff mbox series

V2 [PATCH] x86: Move CET control to _dl_x86_feature_control [BZ #25887]

Message ID CAMe9rOp--haTHrTA4HYEU7aPUMSOFeJ3jgfz-wYB64p-v5NHdQ@mail.gmail.com
State New
Headers show
Series V2 [PATCH] x86: Move CET control to _dl_x86_feature_control [BZ #25887] | expand

Commit Message

H.J. Lu May 18, 2020, 12:26 p.m. UTC
On Mon, May 18, 2020 at 12:19 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> * H. J. Lu via Libc-alpha:
>
> > Here is the updated patch to use bitfields.
>
> Thanks, I like this better.
>
> > diff --git a/sysdeps/x86/cet-tunables.h b/sysdeps/x86/cet-control.h
> > similarity index 61%
> > rename from sysdeps/x86/cet-tunables.h
> > rename to sysdeps/x86/cet-control.h
> > index 5e1e42df10..3a314f9609 100644
> > --- a/sysdeps/x86/cet-tunables.h
> > +++ b/sysdeps/x86/cet-control.h
> > @@ -16,14 +16,26 @@
> >     License along with the GNU C Library; if not, see
> >     <https://www.gnu.org/licenses/>.  */
> >
> > -/* Valid control values:
> > -   0: Enable CET features based on ELF property note.
> > -   1: Always disable CET features.
> > -   2: Always enable CET features.
> > -   3: Enable CET features permissively.
> > - */
> > -#define CET_ELF_PROPERTY     0
> > -#define CET_ALWAYS_OFF               1
> > -#define CET_ALWAYS_ON                2
> > -#define CET_PERMISSIVE               3
> > -#define CET_MAX                      CET_PERMISSIVE
> > +#ifndef _CET_CONTROL_H
> > +#define _CET_CONTROL_H
> > +
> > +/* For each CET feature, IBT and SHSTK, valid control values  */
>
> Missing ”.” at end of comment.

Fixed.

> > +enum dl_x86_cet_control
> > +{
> > +  /* Enable CET features based on ELF property note.  */
> > +  elf_property = 0,
> > +  /* Always enable CET features.  */
> > +  always_on,
> > +  /* Always disable CET features. */
> > +  always_off,
> > +  /* Enable CET features permissively. */
>
> Missing double space after “.”.

Fixed.

> > +  permissive
> > +};
>
> Given enum constantse are not not scoped and this is a widely-included
> header, I think you should include at least a “cet_” prefix in these
> enum constants.

Fixed.

> It's still not clear to me why CET control variables have to be in
> _rtld_global.  Regular global variables would likely lead to clearer
> code, I think.  _rtld_global is needed for read-write data that is
> shared with libc/libdl, and this does not seem to apply to CET control
> settings.

We don't have a pure local struct for rtld.  _rtld_local is a hidden
alias of _rtld_global:

extern struct rtld_global _rtld_local
    __attribute__ ((alias ("_rtld_global"), visibility ("hidden")));

struct rtld_global is used to improve IP-relative access.  It may not
be important for x86-64.  But it is still useful for i386 which doesn't
have IP-relative addressing.

Here is the updated patch.  I combined

   Include <dl-procruntime.c> to get architecture specific initializer in
    rtld_global.

OK for master?

Thanks.

Comments

Florian Weimer May 18, 2020, 12:36 p.m. UTC | #1
* H. J. Lu:

>> It's still not clear to me why CET control variables have to be in
>> _rtld_global.  Regular global variables would likely lead to clearer
>> code, I think.  _rtld_global is needed for read-write data that is
>> shared with libc/libdl, and this does not seem to apply to CET control
>> settings.
>
> We don't have a pure local struct for rtld.

Yes, but we could use global variables.

> _rtld_local is a hidden alias of _rtld_global:
>
> extern struct rtld_global _rtld_local
>     __attribute__ ((alias ("_rtld_global"), visibility ("hidden")));
>
> struct rtld_global is used to improve IP-relative access.

Are you sure?  I think it's mainly for sharing data with libc and libdl
through a single symbol.

Data that's not shared should go into a regular global variable, I
think.

> It may not be important for x86-64.  But it is still useful for i386
> which doesn't have IP-relative addressing.

I don't think we use an alternative way to access _rtld_global or
_rtld_global_ro on any target.  Access always happens through a (hidden)
variable.

The patch looks okay to me now.  Thanks!

Florian
diff mbox series

Patch

From cf798745862c0461194f9676a2d1a5ce70dbc7a3 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Tue, 28 Apr 2020 10:05:25 -0700
Subject: [PATCH] x86: Move CET control to _dl_x86_feature_control [BZ #25887]

1. Include <dl-procruntime.c> to get architecture specific initializer in
rtld_global.
2. Change _dl_x86_feature_1[2] to _dl_x86_feature_1.
3. Add _dl_x86_feature_control after _dl_x86_feature_1, which is a
struct of 2 bitfields for IBT and SHSTK control

This fixes [BZ #25887].
---
 elf/rtld.c                                    |  2 +
 sysdeps/i386/dl-machine.h                     |  2 +-
 sysdeps/unix/sysv/linux/x86/cpu-features.c    |  2 +-
 sysdeps/x86/{cet-tunables.h => cet-control.h} | 34 ++++++++++-----
 sysdeps/x86/cpu-features.c                    | 12 +++---
 sysdeps/x86/cpu-tunables.c                    | 31 +++----------
 sysdeps/x86/dl-cet.c                          | 43 +++++++++----------
 sysdeps/x86/dl-procruntime.c                  | 22 +++++++++-
 sysdeps/x86/ldsodefs.h                        |  1 +
 9 files changed, 81 insertions(+), 68 deletions(-)
 rename sysdeps/x86/{cet-tunables.h => cet-control.h} (60%)

diff --git a/elf/rtld.c b/elf/rtld.c
index 5ccc3c2dbb..882b070cc0 100644
--- a/elf/rtld.c
+++ b/elf/rtld.c
@@ -315,6 +315,8 @@  rtld_hidden_def (_dl_starting_up)
    (except those which cannot be added for some reason).  */
 struct rtld_global _rtld_global =
   {
+    /* Get architecture specific initializer.  */
+#include <dl-procruntime.c>
     /* Generally the default presumption without further information is an
      * executable stack but this is not true for all platforms.  */
     ._dl_stack_flags = DEFAULT_STACK_PERMS,
diff --git a/sysdeps/i386/dl-machine.h b/sysdeps/i386/dl-machine.h
index 8af0789a9c..0f08079e48 100644
--- a/sysdeps/i386/dl-machine.h
+++ b/sysdeps/i386/dl-machine.h
@@ -71,7 +71,7 @@  elf_machine_runtime_setup (struct link_map *l, int lazy, int profile)
   extern void _dl_runtime_profile_shstk (Elf32_Word) attribute_hidden;
   /* Check if SHSTK is enabled by kernel.  */
   bool shstk_enabled
-    = (GL(dl_x86_feature_1)[0] & GNU_PROPERTY_X86_FEATURE_1_SHSTK) != 0;
+    = (GL(dl_x86_feature_1) & GNU_PROPERTY_X86_FEATURE_1_SHSTK) != 0;
 
   if (l->l_info[DT_JMPREL] && lazy)
     {
diff --git a/sysdeps/unix/sysv/linux/x86/cpu-features.c b/sysdeps/unix/sysv/linux/x86/cpu-features.c
index d67b300595..fc0e32827d 100644
--- a/sysdeps/unix/sysv/linux/x86/cpu-features.c
+++ b/sysdeps/unix/sysv/linux/x86/cpu-features.c
@@ -34,7 +34,7 @@  static inline void
 x86_setup_tls (void)
 {
   __libc_setup_tls ();
-  THREAD_SETMEM (THREAD_SELF, header.feature_1, GL(dl_x86_feature_1)[0]);
+  THREAD_SETMEM (THREAD_SELF, header.feature_1, GL(dl_x86_feature_1));
 }
 
 #  define ARCH_SETUP_TLS() x86_setup_tls ()
diff --git a/sysdeps/x86/cet-tunables.h b/sysdeps/x86/cet-control.h
similarity index 60%
rename from sysdeps/x86/cet-tunables.h
rename to sysdeps/x86/cet-control.h
index 5e1e42df10..e163a7f55b 100644
--- a/sysdeps/x86/cet-tunables.h
+++ b/sysdeps/x86/cet-control.h
@@ -16,14 +16,26 @@ 
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
-/* Valid control values:
-   0: Enable CET features based on ELF property note.
-   1: Always disable CET features.
-   2: Always enable CET features.
-   3: Enable CET features permissively.
- */
-#define CET_ELF_PROPERTY	0
-#define CET_ALWAYS_OFF		1
-#define CET_ALWAYS_ON		2
-#define CET_PERMISSIVE		3
-#define CET_MAX			CET_PERMISSIVE
+#ifndef _CET_CONTROL_H
+#define _CET_CONTROL_H
+
+/* For each CET feature, IBT and SHSTK, valid control values.  */
+enum dl_x86_cet_control
+{
+  /* Enable CET features based on ELF property note.  */
+  cet_elf_property = 0,
+  /* Always enable CET features.  */
+  cet_always_on,
+  /* Always disable CET features.  */
+  cet_always_off,
+  /* Enable CET features permissively.  */
+  cet_permissive
+};
+
+struct dl_x86_feature_control
+{
+  enum dl_x86_cet_control ibt : 2;
+  enum dl_x86_cet_control shstk : 2;
+};
+
+#endif /* cet-control.h */
diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c
index bfb415f05a..b6d5d9d4b1 100644
--- a/sysdeps/x86/cpu-features.c
+++ b/sysdeps/x86/cpu-features.c
@@ -39,7 +39,6 @@  extern void TUNABLE_CALLBACK (set_x86_shstk) (tunable_val_t *)
 
 #if CET_ENABLED
 # include <dl-cet.h>
-# include <cet-tunables.h>
 #endif
 
 static void
@@ -620,7 +619,7 @@  no_cpuid:
 
   if (cet_status)
     {
-      GL(dl_x86_feature_1)[0] = cet_status;
+      GL(dl_x86_feature_1) = cet_status;
 
 # ifndef SHARED
       /* Check if IBT and SHSTK are enabled by kernel.  */
@@ -644,14 +643,13 @@  no_cpuid:
 
 	      /* Clear the disabled bits in dl_x86_feature_1.  */
 	      if (res == 0)
-		GL(dl_x86_feature_1)[0] &= ~cet_feature;
+		GL(dl_x86_feature_1) &= ~cet_feature;
 	    }
 
 	  /* Lock CET if IBT or SHSTK is enabled in executable.  Don't
-	     lock CET if SHSTK is enabled permissively.  */
-	  if (((GL(dl_x86_feature_1)[1] >> CET_MAX)
-	       & ((1 << CET_MAX) - 1))
-	       != CET_PERMISSIVE)
+	     lock CET if IBT or SHSTK is enabled permissively.  */
+	  if (GL(dl_x86_feature_control).ibt != cet_permissive
+	      && GL(dl_x86_feature_control).shstk != cet_permissive)
 	    dl_cet_lock_cet ();
 	}
 # endif
diff --git a/sysdeps/x86/cpu-tunables.c b/sysdeps/x86/cpu-tunables.c
index 861bd7bcaa..38ad2c2e84 100644
--- a/sysdeps/x86/cpu-tunables.c
+++ b/sysdeps/x86/cpu-tunables.c
@@ -336,28 +336,18 @@  TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
 }
 
 # if CET_ENABLED
-#  include <cet-tunables.h>
 
 attribute_hidden
 void
 TUNABLE_CALLBACK (set_x86_ibt) (tunable_val_t *valp)
 {
   if (DEFAULT_MEMCMP (valp->strval, "on", sizeof ("on")) == 0)
-    {
-      GL(dl_x86_feature_1)[1] &= ~((1 << CET_MAX) - 1);
-      GL(dl_x86_feature_1)[1] |= CET_ALWAYS_ON;
-    }
+    GL(dl_x86_feature_control).ibt = cet_always_on;
   else if (DEFAULT_MEMCMP (valp->strval, "off", sizeof ("off")) == 0)
-    {
-      GL(dl_x86_feature_1)[1] &= ~((1 << CET_MAX) - 1);
-      GL(dl_x86_feature_1)[1] |= CET_ALWAYS_OFF;
-    }
+    GL(dl_x86_feature_control).ibt = cet_always_off;
   else if (DEFAULT_MEMCMP (valp->strval, "permissive",
 			   sizeof ("permissive")) == 0)
-    {
-      GL(dl_x86_feature_1)[1] &= ~((1 << CET_MAX) - 1);
-      GL(dl_x86_feature_1)[1] |= CET_PERMISSIVE;
-    }
+    GL(dl_x86_feature_control).ibt = cet_permissive;
 }
 
 attribute_hidden
@@ -365,21 +355,12 @@  void
 TUNABLE_CALLBACK (set_x86_shstk) (tunable_val_t *valp)
 {
   if (DEFAULT_MEMCMP (valp->strval, "on", sizeof ("on")) == 0)
-    {
-      GL(dl_x86_feature_1)[1] &= ~(((1 << CET_MAX) - 1) << CET_MAX);
-      GL(dl_x86_feature_1)[1] |= (CET_ALWAYS_ON << CET_MAX);
-    }
+    GL(dl_x86_feature_control).shstk = cet_always_on;
   else if (DEFAULT_MEMCMP (valp->strval, "off", sizeof ("off")) == 0)
-    {
-      GL(dl_x86_feature_1)[1] &= ~(((1 << CET_MAX) - 1) << CET_MAX);
-      GL(dl_x86_feature_1)[1] |= (CET_ALWAYS_OFF << CET_MAX);
-    }
+    GL(dl_x86_feature_control).shstk = cet_always_off;
   else if (DEFAULT_MEMCMP (valp->strval, "permissive",
 			   sizeof ("permissive")) == 0)
-    {
-      GL(dl_x86_feature_1)[1] &= ~(((1 << CET_MAX) - 1) << CET_MAX);
-      GL(dl_x86_feature_1)[1] |= (CET_PERMISSIVE << CET_MAX);
-    }
+    GL(dl_x86_feature_control).shstk = cet_permissive;
 }
 # endif
 #endif
diff --git a/sysdeps/x86/dl-cet.c b/sysdeps/x86/dl-cet.c
index c7029f1b51..5524b66038 100644
--- a/sysdeps/x86/dl-cet.c
+++ b/sysdeps/x86/dl-cet.c
@@ -20,7 +20,6 @@ 
 #include <libintl.h>
 #include <ldsodefs.h>
 #include <dl-cet.h>
-#include <cet-tunables.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.
@@ -39,23 +38,23 @@  static void
 dl_cet_check (struct link_map *m, const char *program)
 {
   /* Check how IBT should be enabled.  */
-  unsigned int enable_ibt_type
-    = GL(dl_x86_feature_1)[1] & ((1 << CET_MAX) - 1);
+  enum dl_x86_cet_control enable_ibt_type
+    = GL(dl_x86_feature_control).ibt;
   /* Check how SHSTK should be enabled.  */
-  unsigned int enable_shstk_type
-    = ((GL(dl_x86_feature_1)[1] >> CET_MAX) & ((1 << CET_MAX) - 1));
+  enum dl_x86_cet_control enable_shstk_type
+    = GL(dl_x86_feature_control).shstk;
 
   /* No legacy object check if both IBT and SHSTK are always on.  */
-  if (enable_ibt_type == CET_ALWAYS_ON
-      && enable_shstk_type == CET_ALWAYS_ON)
+  if (enable_ibt_type == cet_always_on
+      && enable_shstk_type == cet_always_on)
     return;
 
   /* Check if IBT is enabled by kernel.  */
   bool ibt_enabled
-    = (GL(dl_x86_feature_1)[0] & GNU_PROPERTY_X86_FEATURE_1_IBT) != 0;
+    = (GL(dl_x86_feature_1) & GNU_PROPERTY_X86_FEATURE_1_IBT) != 0;
   /* Check if SHSTK is enabled by kernel.  */
   bool shstk_enabled
-    = (GL(dl_x86_feature_1)[0] & GNU_PROPERTY_X86_FEATURE_1_SHSTK) != 0;
+    = (GL(dl_x86_feature_1) & GNU_PROPERTY_X86_FEATURE_1_SHSTK) != 0;
 
   if (ibt_enabled || shstk_enabled)
     {
@@ -65,9 +64,9 @@  dl_cet_check (struct link_map *m, const char *program)
 
       /* Check if IBT and SHSTK are enabled in object.  */
       bool enable_ibt = (ibt_enabled
-			 && enable_ibt_type != CET_ALWAYS_OFF);
+			 && enable_ibt_type != cet_always_off);
       bool enable_shstk = (shstk_enabled
-			   && enable_shstk_type != CET_ALWAYS_OFF);
+			   && enable_shstk_type != cet_always_off);
       if (program)
 	{
 	  /* Enable IBT and SHSTK only if they are enabled in executable.
@@ -76,10 +75,10 @@  dl_cet_check (struct link_map *m, const char *program)
 	     GLIBC_TUNABLES=glibc.cpu.hwcaps=-IBT,-SHSTK
 	   */
 	  enable_ibt &= (HAS_CPU_FEATURE (IBT)
-			 && (enable_ibt_type == CET_ALWAYS_ON
+			 && (enable_ibt_type == cet_always_on
 			     || (m->l_cet & lc_ibt) != 0));
 	  enable_shstk &= (HAS_CPU_FEATURE (SHSTK)
-			   && (enable_shstk_type == CET_ALWAYS_ON
+			   && (enable_shstk_type == cet_always_on
 			       || (m->l_cet & lc_shstk) != 0));
 	}
 
@@ -111,7 +110,7 @@  dl_cet_check (struct link_map *m, const char *program)
 
 	      /* IBT is enabled only if it is enabled in executable as
 		 well as all shared objects.  */
-	      enable_ibt &= (enable_ibt_type == CET_ALWAYS_ON
+	      enable_ibt &= (enable_ibt_type == cet_always_on
 			     || (l->l_cet & lc_ibt) != 0);
 	      if (!found_ibt_legacy && enable_ibt != ibt_enabled)
 		{
@@ -121,7 +120,7 @@  dl_cet_check (struct link_map *m, const char *program)
 
 	      /* SHSTK is enabled only if it is enabled in executable as
 		 well as all shared objects.  */
-	      enable_shstk &= (enable_shstk_type == CET_ALWAYS_ON
+	      enable_shstk &= (enable_shstk_type == cet_always_on
 			       || (l->l_cet & lc_shstk) != 0);
 	      if (enable_shstk != shstk_enabled)
 		{
@@ -137,7 +136,7 @@  dl_cet_check (struct link_map *m, const char *program)
 	{
 	  if (!program)
 	    {
-	      if (enable_ibt_type != CET_PERMISSIVE)
+	      if (enable_ibt_type != cet_permissive)
 		{
 		  /* When IBT is enabled, we cannot dlopen a shared
 		     object without IBT.  */
@@ -148,7 +147,7 @@  dl_cet_check (struct link_map *m, const char *program)
 				      N_("rebuild shared object with IBT support enabled"));
 		}
 
-	      if (enable_shstk_type != CET_PERMISSIVE)
+	      if (enable_shstk_type != cet_permissive)
 		{
 		  /* When SHSTK is enabled, we cannot dlopen a shared
 		     object without SHSTK.  */
@@ -159,8 +158,8 @@  dl_cet_check (struct link_map *m, const char *program)
 				      N_("rebuild shared object with SHSTK support enabled"));
 		}
 
-	      if (enable_ibt_type != CET_PERMISSIVE
-		  && enable_shstk_type != CET_PERMISSIVE)
+	      if (enable_ibt_type != cet_permissive
+		  && enable_shstk_type != cet_permissive)
 		return;
 	    }
 
@@ -190,7 +189,7 @@  dl_cet_check (struct link_map *m, const char *program)
 	    }
 
 	  /* Clear the disabled bits in dl_x86_feature_1.  */
-	  GL(dl_x86_feature_1)[0] &= ~cet_feature;
+	  GL(dl_x86_feature_1) &= ~cet_feature;
 
 	  cet_feature_changed = true;
 	}
@@ -199,9 +198,9 @@  dl_cet_check (struct link_map *m, const char *program)
       if (program && (ibt_enabled || shstk_enabled))
 	{
 	  if ((!ibt_enabled
-	       || enable_ibt_type != CET_PERMISSIVE)
+	       || enable_ibt_type != cet_permissive)
 	      && (!shstk_enabled
-		  || enable_shstk_type != CET_PERMISSIVE))
+		  || enable_shstk_type != cet_permissive))
 	    {
 	      /* Lock CET if IBT or SHSTK is enabled in executable unless
 	         IBT or SHSTK is enabled permissively.  */
diff --git a/sysdeps/x86/dl-procruntime.c b/sysdeps/x86/dl-procruntime.c
index 5e39a38133..2c3e97952b 100644
--- a/sysdeps/x86/dl-procruntime.c
+++ b/sysdeps/x86/dl-procruntime.c
@@ -47,7 +47,27 @@ 
 # if !defined PROCINFO_DECL && defined SHARED
   ._dl_x86_feature_1
 # else
-PROCINFO_CLASS unsigned int _dl_x86_feature_1[2]
+PROCINFO_CLASS unsigned int _dl_x86_feature_1
+# endif
+# ifndef PROCINFO_DECL
+= 0
+# endif
+# if !defined SHARED || defined PROCINFO_DECL
+;
+# else
+,
+# endif
+
+# if !defined PROCINFO_DECL && defined SHARED
+  ._dl_x86_feature_control
+# else
+PROCINFO_CLASS struct dl_x86_feature_control _dl_x86_feature_control
+# endif
+# ifndef PROCINFO_DECL
+= {
+    .ibt = cet_elf_property,
+    .shstk = cet_elf_property
+  }
 # endif
 # if !defined SHARED || defined PROCINFO_DECL
 ;
diff --git a/sysdeps/x86/ldsodefs.h b/sysdeps/x86/ldsodefs.h
index 072f826666..5b1b09dbf8 100644
--- a/sysdeps/x86/ldsodefs.h
+++ b/sysdeps/x86/ldsodefs.h
@@ -61,6 +61,7 @@  struct La_x32_retval;
 				     struct La_x86_64_retval *,		\
 				     const char *)
 
+#include <cet-control.h>
 #include_next <ldsodefs.h>
 
 #endif
-- 
2.26.2