From 21468af18e0ed513487e857eed3e8c809197a5fe Mon Sep 17 00:00:00 2001 From: Dragan Mladjenovic 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