x86-64: Remove LD_PREFER_MAP_32BIT_EXEC support [BZ #28656]
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Commit Message
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
Comments
* 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
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.
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.
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.
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?
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.
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.
@@ -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).
deleted file mode 100644
@@ -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 */
deleted file mode 100644
@@ -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
@@ -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
@@ -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)