x86-64: Add glibc.cpu.prefer_map_32bit_exec [BZ #28656]

Crossing 2GB boundaries with indirect calls and jumps can use more
branch prediction resources on Intel Golden Cove CPU (see the
"Misprediction for Branches >2GB" section in Intel 64 and IA-32
Architectures Optimization Reference Manual.)  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 in shared
libraries 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 the tunable, glibc.cpu.prefer_map_32bit_exec,
or the environment variable, LD_PREFER_MAP_32BIT_EXEC.  This works only
between shared libraries or between shared libraries and executables with
addresses below 2GB.  PIEs are usually loaded at a random address above
4GB by the kernel.

6 files changed, 165 insertions, 0 deletions

diff --git a/sysdeps/unix/sysv/linux/x86_64/64/Makefile b/sysdeps/unix/sysv/linux/x86_64/64/Makefile
index a7b6dc5a53..8ff4f27786 100644
--- a/sysdeps/unix/sysv/linux/x86_64/64/Makefile
+++ b/sysdeps/unix/sysv/linux/x86_64/64/Makefile
@@ -1,2 +1,27 @@
 # The default ABI is 64.
 default-abi := 64
+
+ifeq ($(subdir),elf)
+ifneq ($(have-tunables),no)
+
+tests-map-32bit = \
+  tst-map-32bit-1a \
+  tst-map-32bit-1b \
+# tests-map-32bit
+tst-map-32bit-1a-no-pie = yes
+tst-map-32bit-1b-no-pie = yes
+tests += $(tests-map-32bit)
+
+modules-map-32bit = \
+  tst-map-32bit-mod \
+# modules-map-32bit
+modules-names += $(modules-map-32bit)
+
+$(objpfx)tst-map-32bit-mod.so: $(libsupport)
+tst-map-32bit-1a-ENV = LD_PREFER_MAP_32BIT_EXEC=1
+$(objpfx)tst-map-32bit-1a: $(objpfx)tst-map-32bit-mod.so
+tst-map-32bit-1b-ENV = GLIBC_TUNABLES=glibc.cpu.prefer_map_32bit_exec=1
+$(objpfx)tst-map-32bit-1b: $(objpfx)tst-map-32bit-mod.so
+
+endif
+endif
diff --git a/sysdeps/unix/sysv/linux/x86_64/64/dl-tunables.list b/sysdeps/unix/sysv/linux/x86_64/64/dl-tunables.list
new file mode 100644
index 0000000000..0aab52e662
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/x86_64/64/dl-tunables.list
@@ -0,0 +1,29 @@
+# x86-64 specific tunables.
+# Copyright (C) 2023 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/>.
+
+glibc {
+  cpu {
+    prefer_map_32bit_exec {
+      type: INT_32
+      minval: 0
+      maxval: 1
+      env_alias: LD_PREFER_MAP_32BIT_EXEC
+      security_level: SXID_IGNORE
+    }
+  }
+}
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..33dec3f805
--- /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) 2015-2023 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-1a.c b/sysdeps/unix/sysv/linux/x86_64/64/tst-map-32bit-1a.c
new file mode 100644
index 0000000000..abc396589e
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/x86_64/64/tst-map-32bit-1a.c
@@ -0,0 +1,34 @@
+/* Check that LD_PREFER_MAP_32BIT_EXEC works in PDE and shared library.
+   Copyright (C) 2023 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/unix/sysv/linux/x86_64/64/tst-map-32bit-1b.c b/sysdeps/unix/sysv/linux/x86_64/64/tst-map-32bit-1b.c
new file mode 100644
index 0000000000..34ab01c773
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/x86_64/64/tst-map-32bit-1b.c
@@ -0,0 +1 @@
+#include "tst-map-32bit-1a.c"
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..78d4b6133c
--- /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) 2023 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);
+}