[PATCH] x86-64: Remove LD_PREFER_MAP_32BIT_EXEC support [BZ #28656]

[PATCH] x86-64: Remove LD_PREFER_MAP_32BIT_EXEC support [BZ #28656]

[H.J. Lu]

Remove the LD_PREFER_MAP_32BIT_EXEC environment variable support since
the first PT_LOAD segment is no longer executable due to defaulting to
-z separate-code.

This fixes [BZ #28656].
---
 NEWS                                          |  4 ++
 .../unix/sysv/linux/x86_64/64/dl-librecon.h   | 45 -------------------
 .../unix/sysv/linux/x86_64/64/mmap_internal.h | 42 -----------------
 sysdeps/x86/cpu-tunables.c                    |  7 ---
 ...cpu-features-preferred_feature_index_1.def |  1 -
 5 files changed, 4 insertions(+), 95 deletions(-)
 delete mode 100644 sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h
 delete mode 100644 sysdeps/unix/sysv/linux/x86_64/64/mmap_internal.h

diff --git a/NEWS b/NEWS
index 3a04befe8e..bf2b6846fc 100644
--- a/NEWS
+++ b/NEWS
@@ -9,6 +9,10 @@ Version 2.35
 
 Major new features:
 
+* The LD_PREFER_MAP_32BIT_EXEC environment variable support has been
+  removed since the first PT_LOAD segment is no longer executable due
+  to defaulting to -z separate-code.
+
 * Unicode 14.0.0 Support: Character encoding, character type info, and
   transliteration tables are all updated to Unicode 14.0.0, using
   generator scripts contributed by Mike FABIAN (Red Hat).
diff --git a/sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h b/sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h
deleted file mode 100644
index 5b9696e2de..0000000000
--- a/sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h
+++ /dev/null
@@ -1,45 +0,0 @@
-/* Optional code to distinguish library flavours.  x86-64 version.
-   Copyright (C) 2015-2021 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/>.  */
-
-#ifndef _DL_LIBRECON_H
-
-#include <sysdeps/unix/sysv/linux/dl-librecon.h>
-
-/* Recognizing extra environment variables.  For 64-bit applications,
-   branch prediction performance may be negatively impacted when the
-   target of a branch is more than 4GB away from the branch.  Add the
-   Prefer_MAP_32BIT_EXEC bit so that mmap will try to map executable
-   pages with MAP_32BIT first.  NB: MAP_32BIT will map to lower 2GB,
-   not lower 4GB, address.  Prefer_MAP_32BIT_EXEC reduces bits available
-   for address space layout randomization (ASLR).  Prefer_MAP_32BIT_EXEC
-   is always disabled for SUID programs and can be enabled by setting
-   environment variable, LD_PREFER_MAP_32BIT_EXEC.  */
-#define EXTRA_LD_ENVVARS \
-  case 21:								  \
-    if (!__libc_enable_secure						  \
-	&& memcmp (envline, "PREFER_MAP_32BIT_EXEC", 21) == 0)		  \
-      GLRO(dl_x86_cpu_features).preferred[index_arch_Prefer_MAP_32BIT_EXEC] \
-	|= bit_arch_Prefer_MAP_32BIT_EXEC;				  \
-    break;
-
-/* Extra unsecure variables.  The names are all stuffed in a single
-   string which means they have to be terminated with a '\0' explicitly.  */
-#define EXTRA_UNSECURE_ENVVARS \
-  "LD_PREFER_MAP_32BIT_EXEC\0"
-
-#endif /* dl-librecon.h */
diff --git a/sysdeps/unix/sysv/linux/x86_64/64/mmap_internal.h b/sysdeps/unix/sysv/linux/x86_64/64/mmap_internal.h
deleted file mode 100644
index 18177d2cb3..0000000000
--- a/sysdeps/unix/sysv/linux/x86_64/64/mmap_internal.h
+++ /dev/null
@@ -1,42 +0,0 @@
-/* Linux mmap system call.  x86-64 version.
-   Copyright (C) 2015-2021 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/>.  */
-
-#ifndef MMAP_X86_64_INTERNAL_H
-#define MMAP_X86_64_INTERNAL_H
-
-#include <ldsodefs.h>
-
-/* If the Prefer_MAP_32BIT_EXEC bit is set, try to map executable pages
-   with MAP_32BIT first.  */
-#define MMAP_PREPARE(addr, len, prot, flags, fd, offset)		\
-  if ((addr) == NULL							\
-      && ((prot) & PROT_EXEC) != 0					\
-      && HAS_ARCH_FEATURE (Prefer_MAP_32BIT_EXEC))			\
-    {									\
-      void *ret = (void*) INLINE_SYSCALL_CALL (mmap, (addr), (len),	\
-					      (prot),			\
-					      (flags) | MAP_32BIT,	\
-					      (fd), (offset));		\
-      if (ret != MAP_FAILED)						\
-	return ret;							\
-    }
-
-#include_next <mmap_internal.h>
-
-#endif
diff --git a/sysdeps/x86/cpu-tunables.c b/sysdeps/x86/cpu-tunables.c
index 61b05e5b1d..957db3ad22 100644
--- a/sysdeps/x86/cpu-tunables.c
+++ b/sysdeps/x86/cpu-tunables.c
@@ -258,13 +258,6 @@ TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
 		 20);
 	    }
 	  break;
-	case 21:
-	    {
-	      CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features,
-						Prefer_MAP_32BIT_EXEC,
-						disable, 21);
-	    }
-	  break;
 	case 23:
 	    {
 	      CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH
diff --git a/sysdeps/x86/include/cpu-features-preferred_feature_index_1.def b/sysdeps/x86/include/cpu-features-preferred_feature_index_1.def
index 1530d594b3..8250bfcbec 100644
--- a/sysdeps/x86/include/cpu-features-preferred_feature_index_1.def
+++ b/sysdeps/x86/include/cpu-features-preferred_feature_index_1.def
@@ -26,7 +26,6 @@ BIT (I586)
 BIT (I686)
 BIT (Slow_SSE4_2)
 BIT (AVX_Fast_Unaligned_Load)
-BIT (Prefer_MAP_32BIT_EXEC)
 BIT (Prefer_No_VZEROUPPER)
 BIT (Prefer_ERMS)
 BIT (Prefer_No_AVX512)
-- 
2.33.1

Re: [PATCH] x86-64: Remove LD_PREFER_MAP_32BIT_EXEC support [BZ #28656]

[Florian Weimer]

* H. J. Lu:

> Remove the LD_PREFER_MAP_32BIT_EXEC environment variable support since
> the first PT_LOAD segment is no longer executable due to defaulting to
> -z separate-code.
>
> This fixes [BZ #28656].
> ---
>  NEWS                                          |  4 ++
>  .../unix/sysv/linux/x86_64/64/dl-librecon.h   | 45 -------------------
>  .../unix/sysv/linux/x86_64/64/mmap_internal.h | 42 -----------------
>  sysdeps/x86/cpu-tunables.c                    |  7 ---
>  ...cpu-features-preferred_feature_index_1.def |  1 -
>  5 files changed, 4 insertions(+), 95 deletions(-)
>  delete mode 100644 sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h
>  delete mode 100644 sysdeps/unix/sysv/linux/x86_64/64/mmap_internal.h

Patch looks good to me.

Reviewed-by: Florian Weimer <fweimer@redhat.com>

Thanks,
Florian

Re: [PATCH] x86-64: Remove LD_PREFER_MAP_32BIT_EXEC support [BZ #28656]

[Joseph Myers]

On Fri, 10 Dec 2021, H.J. Lu via Libc-alpha wrote:

>  Major new features:
>  
> +* The LD_PREFER_MAP_32BIT_EXEC environment variable support has been
> +  removed since the first PT_LOAD segment is no longer executable due
> +  to defaulting to -z separate-code.

I don't think "Major new features" is the right place for this.  I think 
it belongs under "Deprecated and removed features, and other changes 
affecting compatibility" instead.

-- 
Joseph S. Myers
joseph@codesourcery.com

[PATCH] NEWS: Move LD_PREFER_MAP_32BIT_EXEC

[H.J. Lu]

[-- Attachment #1: Type: text/plain, Size: 586 bytes --]

On Mon, Dec 13, 2021 at 3:10 PM Joseph Myers <joseph@codesourcery.com> wrote:
>
> On Fri, 10 Dec 2021, H.J. Lu via Libc-alpha wrote:
>
> >  Major new features:
> >
> > +* The LD_PREFER_MAP_32BIT_EXEC environment variable support has been
> > +  removed since the first PT_LOAD segment is no longer executable due
> > +  to defaulting to -z separate-code.
>
> I don't think "Major new features" is the right place for this.  I think
> it belongs under "Deprecated and removed features, and other changes
> affecting compatibility" instead.
>
>

I am checking in this.

Thanks.

-- 
H.J.

[-- Attachment #2: 0001-NEWS-Move-LD_PREFER_MAP_32BIT_EXEC.patch --]
[-- Type: application/x-patch, Size: 1360 bytes --]

Re: [PATCH] NEWS: Move LD_PREFER_MAP_32BIT_EXEC

[Andreas Schwab]

On Dez 13 2021, H.J. Lu via Libc-alpha wrote:

> +* The LD_PREFER_MAP_32BIT_EXEC environment variable support has been
> +  removed since the first PT_LOAD segment is no longer executable due
> +  to defaulting to -z separate-code.

That should probably say that it is an x86-64-only feature.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."

[PATCH] NEWS: Document LD_PREFER_MAP_32BIT_EXEC as x86-64 only

[H.J. Lu]

[-- Attachment #1: Type: text/plain, Size: 410 bytes --]

On Tue, Dec 14, 2021 at 12:43 AM Andreas Schwab <schwab@linux-m68k.org> wrote:
>
> On Dez 13 2021, H.J. Lu via Libc-alpha wrote:
>
> > +* The LD_PREFER_MAP_32BIT_EXEC environment variable support has been
> > +  removed since the first PT_LOAD segment is no longer executable due
> > +  to defaulting to -z separate-code.
>
> That should probably say that it is an x86-64-only feature.
>

Like this?

-- 
H.J.

[-- Attachment #2: 0001-NEWS-Document-LD_PREFER_MAP_32BIT_EXEC-as-x86-64-onl.patch --]
[-- Type: application/x-patch, Size: 1016 bytes --]

Re: [PATCH] NEWS: Document LD_PREFER_MAP_32BIT_EXEC as x86-64 only

[Andreas Schwab]

On Dez 14 2021, H.J. Lu wrote:

> +* The x86-64 LD_PREFER_MAP_32BIT_EXEC environment variable support has
> +  been removed since the first PT_LOAD segment is no longer executable
> +  due to defaulting to -z separate-code.

Perhaps better:
     On x86-64, the LD_PREFER_MAP_32BIT_EXEC ...

since the -z separate-code default is x86-only too.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."

[PATCH v2] NEWS: Document LD_PREFER_MAP_32BIT_EXEC as x86-64 only

[H.J. Lu]

[-- Attachment #1: Type: text/plain, Size: 506 bytes --]

On Tue, Dec 14, 2021 at 7:41 AM Andreas Schwab <schwab@linux-m68k.org> wrote:
>
> On Dez 14 2021, H.J. Lu wrote:
>
> > +* The x86-64 LD_PREFER_MAP_32BIT_EXEC environment variable support has
> > +  been removed since the first PT_LOAD segment is no longer executable
> > +  due to defaulting to -z separate-code.
>
> Perhaps better:
>      On x86-64, the LD_PREFER_MAP_32BIT_EXEC ...
>
> since the -z separate-code default is x86-only too.
>

Fixed.

This is the patch I am checking in.

Thanks.

-- 
H.J.

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