commit ea5814467a02c9d2d7608b6445c5d60e2a81d3ee
Author: H.J. Lu <hjl.tools@gmail.com>
Date: Fri Dec 10 13:00:09 2021 -0800
x86-64: Remove LD_PREFER_MAP_32BIT_EXEC support [BZ #28656]
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].
Reviewed-by: Florian Weimer <fweimer@redhat.com>
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 5b9696e2de8e5482..0000000000000000
--- 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 18177d2cb3ae645f..0000000000000000
--- 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 00fe5045eb56eb07..58f2fad4323d5d91 100644
--- a/sysdeps/x86/cpu-tunables.c
+++ b/sysdeps/x86/cpu-tunables.c
@@ -260,13 +260,6 @@ 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 d7c93f00c5928a30..3bdc76cf71007948 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)