[PATCH] x86-64: Restore LD_PREFER_MAP_32BIT_EXEC support [BZ #28656]
H.J. Lu
hjl.tools@gmail.com
Mon Aug 1 19:51:50 GMT 2022
Crossing 2GB boundaries with indirect calls and jumps can use more
branch prediction resources on several Intel CPUs. There is visible
performance improvement on workloads with many PLT calls when executable
and shared libraries are mmapped below 2GB. Add the Prefer_MAP_32BIT_EXEC
bit so that mmap will try to map executable or denywrite pages with
MAP_32BIT first.
NB: Prefer_MAP_32BIT_EXEC reduces bits available for address space
layout randomization (ASLR), which is always disabled for SUID programs
and can only be enabled by setting environment variable,
LD_PREFER_MAP_32BIT_EXEC.
---
elf/dl-support.c | 4 ++
elf/rtld.c | 20 ++++++++-
sysdeps/generic/dl-librecon.h | 24 +++++++++++
sysdeps/unix/sysv/linux/x86_64/64/Makefile | 19 ++++++++
.../unix/sysv/linux/x86_64/64/dl-librecon.h | 43 +++++++++++++++++++
.../unix/sysv/linux/x86_64/64/mmap_internal.h | 43 +++++++++++++++++++
.../sysv/linux/x86_64/64/tst-map-32bit-mod.c | 33 ++++++++++++++
.../unix/sysv/linux/x86_64/64/tst-map-32bit.c | 34 +++++++++++++++
sysdeps/x86/cpu-tunables.c | 7 +++
...cpu-features-preferred_feature_index_1.def | 1 +
10 files changed, 226 insertions(+), 2 deletions(-)
create mode 100644 sysdeps/generic/dl-librecon.h
create mode 100644 sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h
create mode 100644 sysdeps/unix/sysv/linux/x86_64/64/mmap_internal.h
create mode 100644 sysdeps/unix/sysv/linux/x86_64/64/tst-map-32bit-mod.c
create mode 100644 sysdeps/unix/sysv/linux/x86_64/64/tst-map-32bit.c
diff --git a/elf/dl-support.c b/elf/dl-support.c
index 4af0b5b2ce..7160bdfcf1 100644
--- a/elf/dl-support.c
+++ b/elf/dl-support.c
@@ -35,6 +35,7 @@
#include <dl-machine.h>
#include <libc-lock.h>
#include <dl-cache.h>
+#include <dl-librecon.h>
#include <dl-procinfo.h>
#include <unsecvars.h>
#include <hp-timing.h>
@@ -300,6 +301,9 @@ _dl_non_dynamic_init (void)
{
static const char unsecure_envvars[] =
UNSECURE_ENVVARS
+#ifdef EXTRA_UNSECURE_ENVVARS
+ EXTRA_UNSECURE_ENVVARS
+#endif
;
const char *cp = unsecure_envvars;
diff --git a/elf/rtld.c b/elf/rtld.c
index cbbaf4a331..2ca8c128a3 100644
--- a/elf/rtld.c
+++ b/elf/rtld.c
@@ -32,6 +32,7 @@
#include <fpu_control.h>
#include <hp-timing.h>
#include <libc-lock.h>
+#include <dl-librecon.h>
#include <unsecvars.h>
#include <dl-cache.h>
#include <dl-osinfo.h>
@@ -2681,14 +2682,29 @@ process_envvars (struct dl_main_state *state)
= _dl_strtoul (&envline[21], NULL) > 1;
}
break;
+
+ /* We might have some extra environment variable to handle. This
+ is tricky due to the pre-processing of the length of the name
+ in the switch statement here. The code here assumes that added
+ environment variables have a different length. */
+#ifdef EXTRA_LD_ENVVARS
+ EXTRA_LD_ENVVARS
+#endif
}
}
/* Extra security for SUID binaries. Remove all dangerous environment
variables. */
- if (__glibc_unlikely (__libc_enable_secure))
+ if (__builtin_expect (__libc_enable_secure, 0))
{
- const char *nextp = UNSECURE_ENVVARS;
+ static const char unsecure_envvars[] =
+#ifdef EXTRA_UNSECURE_ENVVARS
+ EXTRA_UNSECURE_ENVVARS
+#endif
+ UNSECURE_ENVVARS;
+ const char *nextp;
+
+ nextp = unsecure_envvars;
do
{
unsetenv (nextp);
diff --git a/sysdeps/generic/dl-librecon.h b/sysdeps/generic/dl-librecon.h
new file mode 100644
index 0000000000..19fc70cb29
--- /dev/null
+++ b/sysdeps/generic/dl-librecon.h
@@ -0,0 +1,24 @@
+/* Optional code to distinguish library flavours.
+ Copyright (C) 1998-2022 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
+#define _DL_LIBRECON_H 1
+
+/* In the general case we don't do anything. */
+
+#endif /* dl-librecon.h */
diff --git a/sysdeps/unix/sysv/linux/x86_64/64/Makefile b/sysdeps/unix/sysv/linux/x86_64/64/Makefile
index a7b6dc5a53..53a401e35e 100644
--- a/sysdeps/unix/sysv/linux/x86_64/64/Makefile
+++ b/sysdeps/unix/sysv/linux/x86_64/64/Makefile
@@ -1,2 +1,21 @@
# The default ABI is 64.
default-abi := 64
+
+ifeq ($(subdir),elf)
+
+tests-map-32bit = \
+ tst-map-32bit \
+# tests-map-32bit
+tst-map-32bit-no-pie = yes
+tests += $(tests-map-32bit)
+
+modules-map-32bit = \
+ tst-map-32bit-mod \
+# modules-map-32bit
+modules-names += $(modules-map-32bit)
+
+tst-map-32bit-ENV = LD_PREFER_MAP_32BIT_EXEC=1
+$(objpfx)tst-map-32bit-mod.so: $(libsupport)
+$(objpfx)tst-map-32bit: $(objpfx)tst-map-32bit-mod.so
+
+endif
diff --git a/sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h b/sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h
new file mode 100644
index 0000000000..246abccd45
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h
@@ -0,0 +1,43 @@
+/* Optional code to distinguish library flavours. x86-64 version.
+ Copyright (C) 2015-2022 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
+
+/* 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
new file mode 100644
index 0000000000..7a3c18fb7b
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/x86_64/64/mmap_internal.h
@@ -0,0 +1,43 @@
+/* Linux mmap system call. x86-64 version.
+ Copyright (C) 2015-2022 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 or
+ denywrite pages with MAP_32BIT first. */
+#define MMAP_PREPARE(addr, len, prot, flags, fd, offset) \
+ if ((addr) == NULL \
+ && (((prot) & PROT_EXEC) != 0 \
+ || ((flags) & MAP_DENYWRITE) != 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/unix/sysv/linux/x86_64/64/tst-map-32bit-mod.c b/sysdeps/unix/sysv/linux/x86_64/64/tst-map-32bit-mod.c
new file mode 100644
index 0000000000..0e44d17105
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/x86_64/64/tst-map-32bit-mod.c
@@ -0,0 +1,33 @@
+/* Check that LD_PREFER_MAP_32BIT_EXEC works in shared library.
+ Copyright (C) 2022 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 <stdint.h>
+#include <support/check.h>
+
+static void
+dso_do_test (void)
+{
+}
+
+void
+dso_check_map_32bit (void)
+{
+ printf ("dso_do_test: %p\n", dso_do_test);
+ TEST_VERIFY ((uintptr_t) dso_do_test < 0xffffffffUL);
+}
diff --git a/sysdeps/unix/sysv/linux/x86_64/64/tst-map-32bit.c b/sysdeps/unix/sysv/linux/x86_64/64/tst-map-32bit.c
new file mode 100644
index 0000000000..ed96d8a4d0
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/x86_64/64/tst-map-32bit.c
@@ -0,0 +1,34 @@
+/* Check that LD_PREFER_MAP_32BIT_EXEC works in PIE and shared library.
+ Copyright (C) 2022 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 <stdint.h>
+#include <support/check.h>
+
+extern void dso_check_map_32bit (void);
+
+static int
+do_test (void)
+{
+ printf ("do_test: %p\n", do_test);
+ TEST_VERIFY ((uintptr_t) do_test < 0xffffffffUL);
+ dso_check_map_32bit ();
+ return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/sysdeps/x86/cpu-tunables.c b/sysdeps/x86/cpu-tunables.c
index 94f4fbf243..8b4dfaa5b3 100644
--- a/sysdeps/x86/cpu-tunables.c
+++ b/sysdeps/x86/cpu-tunables.c
@@ -259,6 +259,13 @@ 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 0e9090e74b..2b2c884be9 100644
--- a/sysdeps/x86/include/cpu-features-preferred_feature_index_1.def
+++ b/sysdeps/x86/include/cpu-features-preferred_feature_index_1.def
@@ -26,6 +26,7 @@ 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)
--
2.37.1
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