[glibc/release/2.28/master] mips: Force RWX stack for hard-float builds that can run on pre-4.8 kernels

[Adhemerval Zanella <azanella at sourceware dot org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=fe7c01cb14bd78943eb6c6a483f59299b7aebdc0

commit fe7c01cb14bd78943eb6c6a483f59299b7aebdc0
Author: Dragan Mladjenovic <dmladjenovic@wavecomp.com>
Date:   Fri Aug 23 16:38:04 2019 +0000

    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)

Diff:
---
 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 8217f42..03044e7 100644
--- a/sysdeps/unix/sysv/linux/mips/Makefile
+++ b/sysdeps/unix/sysv/linux/mips/Makefile
@@ -63,14 +63,25 @@ 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 1ee7f41..25f98e0 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}])