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 --git a/ChangeLog b/ChangeLog
index a9115738e0a659627be5edcbed360521d810b9ad..3ca1f72be02276345a5005922000df356e348529 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,19 @@
+2019-11-01  Dragan Mladjenovic  <dmladjenovic@wavecomp.com>
+
+       * 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.
+
 2019-02-04  H.J. Lu  <hongjiu.lu@intel.com>
 
        [BZ #24155]

diff --git a/sysdeps/unix/sysv/linux/mips/Makefile b/sysdeps/unix/sysv/linux/mips/Makefile
index c6729c15f927c14a618e6ed07c875a66f08e8a92..a58e6954a71f69ac53ee4cd9809cd20a40456d07 100644 (file)
--- 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 a5513fad489251745eaeae3cc2468068a23d976b..2ec86a312127194360fb99698e9e8715ab670198 100644 (file)
--- 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 9147aa4582b987eb39777e807f82d64a0d021537..3db1b32b085083ccdd631a1b604a47f2f729f85d 100644 (file)
--- 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}])