Backport of mips: Force RWX stack for hard-float builds that can run on pre-4.8 kernels

[Dragan Mladjenovic <dmladjenovic@wavecomp.com>]

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Hello everybody,

Not sure if this is the right procedure, but I wish to propose the 
back-porting of [1] to most of the active release branches. You can find 
more info about the patch on [2]. The patch applies cleanly
(sans the ChangeLog) up to 2.24  where it expects [3] from 2.25.
I've attached both versions for reference.
Checked for o32 hard-float and soft-float (where available) builds.

Best regards,
Dragan


[1] 
https://sourceware.org/git/?p=glibc.git;a=commit;h=33bc9efd91de1b14354291fc8ebd5bce96379f12
[2] https://sourceware.org/ml/libc-alpha/2019-08/msg00479.html
[3] 
https://sourceware.org/git/?p=glibc.git;a=commit;h=7672e712e1cd91a9252bb9db8ac1d9b528e19f2e

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From d6fb2bde4d5c7a90efedb663fdf6947471efecd2 Mon Sep 17 00:00:00 2001
From: Dragan Mladjenovic <dmladjenovic@wavecomp.com>
Date: Fri, 23 Aug 2019 16:38:04 +0000
Subject: [PATCH] mips: Force RWX stack for hard-float builds that can run on
 pre-4.8 kernels

Linux/Mips kernels prior to 4.8 could potentially crash the user
process when doing FPU emulation while running on non-executable
user stack.

Currently, gcc doesn't emit .note.GNU-stack for mips, but that will
change in the future. To ensure that glibc can be used with such
future gcc, without silently resulting in binaries that might crash
in runtime, this patch forces RWX stack for all built objects if
configured to run against minimum kernel version less than 4.8.

	* sysdeps/unix/sysv/linux/mips/Makefile
	(test-xfail-check-execstack):
	Move under mips-has-gnustack != yes.
	(CFLAGS-.o*, ASFLAGS-.o*): New rules.
	Apply -Wa,-execstack if mips-force-execstack == yes.
	* sysdeps/unix/sysv/linux/mips/configure: Regenerated.
	* sysdeps/unix/sysv/linux/mips/configure.ac
	(mips-force-execstack): New var.
	Set to yes for hard-float builds with minimum_kernel < 4.8.0
	or minimum_kernel not set at all.
	(mips-has-gnustack): New var.
	Use value of libc_cv_as_noexecstack
	if mips-force-execstack != yes, otherwise set to no.

(cherry picked from commit 33bc9efd91de1b14354291fc8ebd5bce96379f12)
---
 sysdeps/unix/sysv/linux/mips/Makefile     | 21 ++++++++++++----
 sysdeps/unix/sysv/linux/mips/configure    | 41 +++++++++++++++++++++++++++++++
 sysdeps/unix/sysv/linux/mips/configure.ac | 32 ++++++++++++++++++++++++
 3 files changed, 89 insertions(+), 5 deletions(-)

diff --git a/sysdeps/unix/sysv/linux/mips/Makefile b/sysdeps/unix/sysv/linux/mips/Makefile
index bca11d3..a58e695 100644
--- a/sysdeps/unix/sysv/linux/mips/Makefile
+++ b/sysdeps/unix/sysv/linux/mips/Makefile
@@ -99,14 +99,25 @@ sysdep-dl-routines += dl-static
 
 sysdep_routines += dl-vdso
 endif
-
-# Supporting non-executable stacks on MIPS requires changes to both
-# the Linux kernel and glibc.  See
-# <https://sourceware.org/ml/libc-alpha/2016-01/msg00567.html> and
-# <https://sourceware.org/ml/libc-alpha/2016-01/msg00719.html>.
+# If the compiler doesn't use GNU.stack note,
+# this test is expected to fail.
+ifneq ($(mips-has-gnustack),yes)
 test-xfail-check-execstack = yes
 endif
+endif
 
 ifeq ($(subdir),stdlib)
 gen-as-const-headers += ucontext_i.sym
 endif
+
+ifeq ($(mips-force-execstack),yes)
+CFLAGS-.o += -Wa,-execstack
+CFLAGS-.os += -Wa,-execstack
+CFLAGS-.op += -Wa,-execstack
+CFLAGS-.oS += -Wa,-execstack
+
+ASFLAGS-.o += -Wa,-execstack
+ASFLAGS-.os += -Wa,-execstack
+ASFLAGS-.op += -Wa,-execstack
+ASFLAGS-.oS += -Wa,-execstack
+endif
diff --git a/sysdeps/unix/sysv/linux/mips/configure b/sysdeps/unix/sysv/linux/mips/configure
index a5513fa..2ec86a3 100644
--- a/sysdeps/unix/sysv/linux/mips/configure
+++ b/sysdeps/unix/sysv/linux/mips/configure
@@ -475,3 +475,44 @@ if test -z "$arch_minimum_kernel"; then
     arch_minimum_kernel=4.5.0
   fi
 fi
+
+# Check if we are supposed to run on kernels older than 4.8.0. If so,
+# force executable stack to avoid potential runtime problems with fpu
+# emulation.
+# NOTE: The check below assumes that in absence of user-provided minumum_kernel
+# we will default to arch_minimum_kernel which is currently less than 4.8.0 for
+# all known configurations. If this changes, the check must be updated.
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler must use executable stack" >&5
+$as_echo_n "checking whether the compiler must use executable stack... " >&6; }
+if ${libc_cv_mips_force_execstack+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  libc_cv_mips_force_execstack=no
+  if test $libc_mips_float = hard; then
+    if test -n "$minimum_kernel"; then
+
+       min_version=$((`echo "$minimum_kernel.0.0.0" | sed 's/\([0-9]*\)\.\([0-9]*\)\.\([0-9]*\).*/\1 \* 65536 + \2 \* 256 + \3/'`))
+
+       if test $min_version -lt 264192; then
+         libc_cv_mips_force_execstack=yes
+       fi
+    else
+      libc_cv_mips_force_execstack=yes
+    fi
+  fi
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_mips_force_execstack" >&5
+$as_echo "$libc_cv_mips_force_execstack" >&6; }
+
+libc_mips_has_gnustack=$libc_cv_as_noexecstack
+
+if test $libc_cv_mips_force_execstack = yes; then
+  libc_mips_has_gnustack=no
+  { $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: forcing executable stack for pre-4.8.0 Linux kernels" >&5
+$as_echo "$as_me: WARNING: forcing executable stack for pre-4.8.0 Linux kernels" >&2;}
+fi
+
+config_vars="$config_vars
+mips-force-execstack = ${libc_cv_mips_force_execstack}"
+config_vars="$config_vars
+mips-has-gnustack = ${libc_mips_has_gnustack}"
diff --git a/sysdeps/unix/sysv/linux/mips/configure.ac b/sysdeps/unix/sysv/linux/mips/configure.ac
index 9147aa4..3db1b32 100644
--- a/sysdeps/unix/sysv/linux/mips/configure.ac
+++ b/sysdeps/unix/sysv/linux/mips/configure.ac
@@ -134,3 +134,35 @@ if test -z "$arch_minimum_kernel"; then
     arch_minimum_kernel=4.5.0
   fi
 fi
+
+# Check if we are supposed to run on kernels older than 4.8.0. If so,
+# force executable stack to avoid potential runtime problems with fpu
+# emulation.
+# NOTE: The check below assumes that in absence of user-provided minumum_kernel
+# we will default to arch_minimum_kernel which is currently less than 4.8.0 for
+# all known configurations. If this changes, the check must be updated.
+AC_CACHE_CHECK([whether the compiler must use executable stack],
+        libc_cv_mips_force_execstack, [dnl
+libc_cv_mips_force_execstack=no
+  if test $libc_mips_float = hard; then
+    if test -n "$minimum_kernel"; then
+       changequote(,)
+       min_version=$((`echo "$minimum_kernel.0.0.0" | sed 's/\([0-9]*\)\.\([0-9]*\)\.\([0-9]*\).*/\1 \* 65536 + \2 \* 256 + \3/'`))
+       changequote([,])
+       if test $min_version -lt 264192; then
+         libc_cv_mips_force_execstack=yes
+       fi
+    else
+      libc_cv_mips_force_execstack=yes
+    fi
+  fi])
+
+libc_mips_has_gnustack=$libc_cv_as_noexecstack
+
+if test $libc_cv_mips_force_execstack = yes; then
+  libc_mips_has_gnustack=no
+  AC_MSG_WARN([forcing executable stack for pre-4.8.0 Linux kernels])
+fi
+
+LIBC_CONFIG_VAR([mips-force-execstack],[${libc_cv_mips_force_execstack}])
+LIBC_CONFIG_VAR([mips-has-gnustack],[${libc_mips_has_gnustack}])
-- 
1.9.1


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From 21468af18e0ed513487e857eed3e8c809197a5fe Mon Sep 17 00:00:00 2001
From: Dragan Mladjenovic <dmladjenovic@wavecomp.com>
Date: Fri, 23 Aug 2019 16:38:04 +0000
Subject: [PATCH] mips: Force RWX stack for hard-float builds that can run on
 pre-4.8 kernels

Linux/Mips kernels prior to 4.8 could potentially crash the user
process when doing FPU emulation while running on non-executable
user stack.

Currently, gcc doesn't emit .note.GNU-stack for mips, but that will
change in the future. To ensure that glibc can be used with such
future gcc, without silently resulting in binaries that might crash
in runtime, this patch forces RWX stack for all built objects if
configured to run against minimum kernel version less than 4.8.

	* sysdeps/unix/sysv/linux/mips/Makefile
	(test-xfail-check-execstack): New var.
	Set to yes if mips-has-gnustack != yes.
	(CFLAGS-.o*, ASFLAGS-.o*): New rules.
	Apply -Wa,-execstack if mips-force-execstack == yes.
	* sysdeps/unix/sysv/linux/mips/configure: Regenerated.
	* sysdeps/unix/sysv/linux/mips/configure.ac
	(mips-force-execstack): New var.
	Set to yes for hard-float builds with minimum_kernel < 4.8.0
	or minimum_kernel not set at all.
	(mips-has-gnustack): New var.
	Use value of libc_cv_as_noexecstack
	if mips-force-execstack != yes, otherwise set to no.

(cherry picked from commit 33bc9efd91de1b14354291fc8ebd5bce96379f12)
---
 sysdeps/unix/sysv/linux/mips/Makefile     | 17 +++++++++++++
 sysdeps/unix/sysv/linux/mips/configure    | 41 +++++++++++++++++++++++++++++++
 sysdeps/unix/sysv/linux/mips/configure.ac | 32 ++++++++++++++++++++++++
 3 files changed, 90 insertions(+)

diff --git a/sysdeps/unix/sysv/linux/mips/Makefile b/sysdeps/unix/sysv/linux/mips/Makefile
index c6729c1..a58e695 100644
--- a/sysdeps/unix/sysv/linux/mips/Makefile
+++ b/sysdeps/unix/sysv/linux/mips/Makefile
@@ -99,8 +99,25 @@ sysdep-dl-routines += dl-static
 
 sysdep_routines += dl-vdso
 endif
+# If the compiler doesn't use GNU.stack note,
+# this test is expected to fail.
+ifneq ($(mips-has-gnustack),yes)
+test-xfail-check-execstack = yes
+endif
 endif
 
 ifeq ($(subdir),stdlib)
 gen-as-const-headers += ucontext_i.sym
 endif
+
+ifeq ($(mips-force-execstack),yes)
+CFLAGS-.o += -Wa,-execstack
+CFLAGS-.os += -Wa,-execstack
+CFLAGS-.op += -Wa,-execstack
+CFLAGS-.oS += -Wa,-execstack
+
+ASFLAGS-.o += -Wa,-execstack
+ASFLAGS-.os += -Wa,-execstack
+ASFLAGS-.op += -Wa,-execstack
+ASFLAGS-.oS += -Wa,-execstack
+endif
diff --git a/sysdeps/unix/sysv/linux/mips/configure b/sysdeps/unix/sysv/linux/mips/configure
index a5513fa..2ec86a3 100644
--- a/sysdeps/unix/sysv/linux/mips/configure
+++ b/sysdeps/unix/sysv/linux/mips/configure
@@ -475,3 +475,44 @@ if test -z "$arch_minimum_kernel"; then
     arch_minimum_kernel=4.5.0
   fi
 fi
+
+# Check if we are supposed to run on kernels older than 4.8.0. If so,
+# force executable stack to avoid potential runtime problems with fpu
+# emulation.
+# NOTE: The check below assumes that in absence of user-provided minumum_kernel
+# we will default to arch_minimum_kernel which is currently less than 4.8.0 for
+# all known configurations. If this changes, the check must be updated.
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler must use executable stack" >&5
+$as_echo_n "checking whether the compiler must use executable stack... " >&6; }
+if ${libc_cv_mips_force_execstack+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  libc_cv_mips_force_execstack=no
+  if test $libc_mips_float = hard; then
+    if test -n "$minimum_kernel"; then
+
+       min_version=$((`echo "$minimum_kernel.0.0.0" | sed 's/\([0-9]*\)\.\([0-9]*\)\.\([0-9]*\).*/\1 \* 65536 + \2 \* 256 + \3/'`))
+
+       if test $min_version -lt 264192; then
+         libc_cv_mips_force_execstack=yes
+       fi
+    else
+      libc_cv_mips_force_execstack=yes
+    fi
+  fi
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_mips_force_execstack" >&5
+$as_echo "$libc_cv_mips_force_execstack" >&6; }
+
+libc_mips_has_gnustack=$libc_cv_as_noexecstack
+
+if test $libc_cv_mips_force_execstack = yes; then
+  libc_mips_has_gnustack=no
+  { $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: forcing executable stack for pre-4.8.0 Linux kernels" >&5
+$as_echo "$as_me: WARNING: forcing executable stack for pre-4.8.0 Linux kernels" >&2;}
+fi
+
+config_vars="$config_vars
+mips-force-execstack = ${libc_cv_mips_force_execstack}"
+config_vars="$config_vars
+mips-has-gnustack = ${libc_mips_has_gnustack}"
diff --git a/sysdeps/unix/sysv/linux/mips/configure.ac b/sysdeps/unix/sysv/linux/mips/configure.ac
index 9147aa4..3db1b32 100644
--- a/sysdeps/unix/sysv/linux/mips/configure.ac
+++ b/sysdeps/unix/sysv/linux/mips/configure.ac
@@ -134,3 +134,35 @@ if test -z "$arch_minimum_kernel"; then
     arch_minimum_kernel=4.5.0
   fi
 fi
+
+# Check if we are supposed to run on kernels older than 4.8.0. If so,
+# force executable stack to avoid potential runtime problems with fpu
+# emulation.
+# NOTE: The check below assumes that in absence of user-provided minumum_kernel
+# we will default to arch_minimum_kernel which is currently less than 4.8.0 for
+# all known configurations. If this changes, the check must be updated.
+AC_CACHE_CHECK([whether the compiler must use executable stack],
+        libc_cv_mips_force_execstack, [dnl
+libc_cv_mips_force_execstack=no
+  if test $libc_mips_float = hard; then
+    if test -n "$minimum_kernel"; then
+       changequote(,)
+       min_version=$((`echo "$minimum_kernel.0.0.0" | sed 's/\([0-9]*\)\.\([0-9]*\)\.\([0-9]*\).*/\1 \* 65536 + \2 \* 256 + \3/'`))
+       changequote([,])
+       if test $min_version -lt 264192; then
+         libc_cv_mips_force_execstack=yes
+       fi
+    else
+      libc_cv_mips_force_execstack=yes
+    fi
+  fi])
+
+libc_mips_has_gnustack=$libc_cv_as_noexecstack
+
+if test $libc_cv_mips_force_execstack = yes; then
+  libc_mips_has_gnustack=no
+  AC_MSG_WARN([forcing executable stack for pre-4.8.0 Linux kernels])
+fi
+
+LIBC_CONFIG_VAR([mips-force-execstack],[${libc_cv_mips_force_execstack}])
+LIBC_CONFIG_VAR([mips-has-gnustack],[${libc_mips_has_gnustack}])
-- 
1.9.1