Re: [PATCH v6 01/14] Allow glibc to be built with _FORTIFY_SOURCE

[Siddhesh Poyarekar <siddhesh@gotplt.org>]

On 2023-07-05 10:38, Frédéric Bérat wrote:
> Add --enable-fortify-source option.
> 
> It is now possible to enable fortification through a configure option.
> The level may be given as parameter, if none is provided, the configure
> script will determine what is the highest level possible that can be set
> considering GCC built-ins availability and set it.
> If level is explicitly set to 3, configure checks if the compiler
> supports the built-in function necessary for it or raise an error if it
> isn't.
> 
> If the configure option isn't explicitly enabled, it _FORTIFY_SOURCE is
> forcibly undefined (and therefore disabled).
> 
> The result of the configure checks are new variables, ${fortify_source}
> and ${no_fortify_source} that can be used to appropriately populate
> CFLAGS.
> 
> A dedicated patch will follow to make use of this variable in Makefiles
> when necessary.
> 
> Updated NEWS and INSTALL.
> 
> Adding dedicated x86_64 variant that enables the configuration.
> ---
>   INSTALL                      |  8 ++++
>   Makeconfig                   | 35 +++++++++++++--
>   NEWS                         |  6 +++
>   config.make.in               |  3 +-
>   configure                    | 83 ++++++++++++++++++++++++++++--------
>   configure.ac                 | 60 ++++++++++++++++++--------
>   elf/rtld-Rules               |  2 +-
>   manual/install.texi          |  8 ++++
>   scripts/build-many-glibcs.py |  4 +-
>   9 files changed, 167 insertions(+), 42 deletions(-)

LGTM.

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

> 
> diff --git a/INSTALL b/INSTALL
> index fe591c7dae..51297189c0 100644
> --- a/INSTALL
> +++ b/INSTALL
> @@ -276,6 +276,14 @@ if ‘CFLAGS’ is specified it must enable optimization.  For example:
>        the GNU C Library.  The default value refers to the main
>        bug-reporting information for the GNU C Library.
>   
> +‘--enable-fortify-source’
> +‘--enable-fortify-source=LEVEL’
> +     Use -D_FORTIFY_SOURCE=‘LEVEL’ to control hardening in the GNU C
> +     Library.  If not provided, ‘LEVEL’ defaults to highest possible
> +     value supported by the build compiler.
> +
> +     Default is to disable fortification.
> +
>      To build the library and related programs, type ‘make’.  This will
>   produce a lot of output, some of which may look like errors from ‘make’
>   but aren’t.  Look for error messages from ‘make’ containing ‘***’.
> diff --git a/Makeconfig b/Makeconfig
> index 2514db35f6..77d7fd14df 100644
> --- a/Makeconfig
> +++ b/Makeconfig
> @@ -543,12 +543,13 @@ endif  # +link
>   # ARM, gcc always produces different debugging symbols when invoked with
>   # a -O greater than 0 than when invoked with -O0, regardless of anything else
>   # we're using to suppress optimizations.  Therefore, we need to explicitly pass
> -# -O0 to it through CFLAGS.
> +# -O0 to it through CFLAGS. As a result, any fortification needs to be disabled
> +# as it needs -O greater than 0.
>   # Additionally, the build system will try to -include $(common-objpfx)/config.h
>   # when compiling the tests, which will throw an error if some special macros
>   # (such as __OPTIMIZE__ and IS_IN_build) aren't defined.  To avoid this, we
>   # tell gcc to define IS_IN_build.
> -CFLAGS-printers-tests := -O0 -ggdb3 -DIS_IN_build
> +CFLAGS-printers-tests := -O0 -ggdb3 -DIS_IN_build $(no-fortify-source)
>   
>   ifeq (yes,$(build-shared))
>   # These indicate whether to link using the built ld.so or the installed one.
> @@ -901,6 +902,16 @@ define elide-stack-protector
>   $(if $(filter $(@F),$(patsubst %,%$(1),$(2))), $(no-stack-protector))
>   endef
>   
> +# We might want to compile with fortify-source
> +ifneq ($(fortify-source),)
> ++fortify-source=$(fortify-source)
> +endif
> +
> +# Some routine can't be fortified like the ones used by fortify
> +define elide-fortify-source
> +$(if $(filter $(@F),$(patsubst %,%$(1),$(2))), $(no-fortify-source))
> +endef
> +
>   # The program that makes Emacs-style TAGS files.
>   ETAGS	:= etags
>   
> @@ -961,6 +972,18 @@ endif	# $(+cflags) == ""
>   	   $(+stack-protector) -fno-common
>   +gcc-nowarn := -w
>   
> +# We must filter out elf because the early bootstrap of the dynamic loader
> +# cannot be fortified. Likewise we exclude dlfcn because it is entangled
> +# with the loader. We must filter out csu because early startup, like the
> +# loader, cannot be fortified. Lastly debug is the fortification routines
> +# themselves and they cannot be fortified.
> +do-fortify = $(filter-out elf dlfcn csu debug,$(subdir))
> +ifeq ($(do-fortify),$(subdir))
> ++cflags += $(+fortify-source)
> +else
> ++cflags += $(no-fortify-source)
> +endif
> +
>   # Each sysdeps directory can contain header files that both will be
>   # used to compile and will be installed.  Each can also contain an
>   # include/ subdirectory, whose header files will be used to compile
> @@ -1010,7 +1033,7 @@ module-cppflags = $(if $(filter %.mk.i %.v.i,$(@F)),,$(module-cppflags-real))
>   # Note that we can't use -std=* in CPPFLAGS, because it overrides
>   # the implicit -lang-asm and breaks cpp behavior for .S files--notably
>   # it causes cpp to stop predefining __ASSEMBLER__.
> -CPPFLAGS = $(config-extra-cppflags) $(CPPUNDEFS) $(CPPFLAGS-config) \
> +CPPFLAGS = $(config-extra-cppflags) $(CPPFLAGS-config) \
>   	   $($(subdir)-CPPFLAGS) \
>   	   $(+includes) $(defines) $(module-cppflags) \
>   	   -include $(..)include/libc-symbols.h $(sysdep-CPPFLAGS) \
> @@ -1049,6 +1072,8 @@ object-suffixes :=
>   CPPFLAGS-.o = $(pic-default)
>   # libc.a must be compiled with -fPIE/-fpie for static PIE.
>   CFLAGS-.o = $(filter %frame-pointer,$(+cflags)) $(pie-default)
> +CFLAGS-.o += $(call elide-fortify-source,.o,$(routines_no_fortify))
> +CFLAGS-.o += $(call elide-fortify-source,_chk.o,$(routines_no_fortify))
>   libtype.o := lib%.a
>   object-suffixes += .o
>   ifeq (yes,$(build-shared))
> @@ -1058,6 +1083,8 @@ object-suffixes += .os
>   pic-cppflags = -DPIC -DSHARED
>   CPPFLAGS-.os = $(pic-cppflags)
>   CFLAGS-.os = $(filter %frame-pointer,$(+cflags)) $(pic-ccflag)
> +CFLAGS-.os += $(call elide-fortify-source,.os,$(routines_no_fortify))
> +CFLAGS-.os += $(call elide-fortify-source,_chk.os,$(routines_no_fortify))
>   libtype.os := lib%_pic.a
>   # This can be changed by a sysdep makefile
>   pic-ccflag = -fPIC
> @@ -1077,6 +1104,8 @@ object-suffixes += .op
>   CPPFLAGS-.op = -DPROF $(pic-default)
>   # libc_p.a must be compiled with -fPIE/-fpie for static PIE.
>   CFLAGS-.op = -pg $(pie-default)
> +CFLAGS-.op += $(call elide-fortify-source,.op,$(routines_no_fortify))
> +CFLAGS-.op += $(call elide-fortify-source,_chk.op,$(routines_no_fortify))
>   libtype.op = lib%_p.a
>   endif
>   
> diff --git a/NEWS b/NEWS
> index 709ee40e50..f976abccbd 100644
> --- a/NEWS
> +++ b/NEWS
> @@ -48,6 +48,12 @@ Major new features:
>   * The strlcpy and strlcat functions have been added.  They are derived
>     from OpenBSD, and are expected to be added to a future POSIX version.
>   
> +* A new configure option, "--enable-fortify-source", can be used to build the
> +  GNU C Library with _FORTIFY_SOURCE. The level of fortification can either be
> +  provided, or is set to the highest value supported by the compiler. If not
> +  explicitly enabled, then fortify source is forcibly disabled so to keep
> +  original behavior unchanged.
> +
>   Deprecated and removed features, and other changes affecting compatibility:
>   
>   * In the Linux kernel for the hppa/parisc architecture some of the
> diff --git a/config.make.in b/config.make.in
> index 4afd37feaf..d487a4f4e9 100644
> --- a/config.make.in
> +++ b/config.make.in
> @@ -64,6 +64,8 @@ have-fpie = @libc_cv_fpie@
>   have-ssp = @libc_cv_ssp@
>   stack-protector = @stack_protector@
>   no-stack-protector = @no_stack_protector@
> +fortify-source = @fortify_source@
> +no-fortify-source = @no_fortify_source@
>   have-selinux = @have_selinux@
>   have-libaudit = @have_libaudit@
>   have-libcap = @have_libcap@
> @@ -101,7 +103,6 @@ CXX = @CXX@
>   BUILD_CC = @BUILD_CC@
>   CFLAGS = @CFLAGS@
>   CPPFLAGS-config = @CPPFLAGS@
> -CPPUNDEFS = @CPPUNDEFS@
>   extra-nonshared-cflags = @extra_nonshared_cflags@
>   rtld-early-cflags = @rtld_early_cflags@
>   ASFLAGS-config = @ASFLAGS_config@
> diff --git a/configure b/configure
> index f84040644b..1833a4ce66 100755
> --- a/configure
> +++ b/configure
> @@ -611,7 +611,10 @@ libc_cv_gcc_unwind_find_fde
>   libc_extra_cppflags
>   libc_extra_cflags
>   libc_cv_cxx_thread_local
> -CPPUNDEFS
> +fortify_source
> +no_fortify_source
> +libc_cv_fortify_source
> +enable_fortify_source
>   have_selinux
>   have_libcap
>   have_libaudit
> @@ -782,6 +785,7 @@ enable_pt_chown
>   enable_mathvec
>   enable_cet
>   enable_scv
> +enable_fortify_source
>   with_cpu
>   '
>         ac_precious_vars='build_alias
> @@ -1452,6 +1456,10 @@ Optional Features:
>                             (CET), x86 only
>     --disable-scv           syscalls will not use scv instruction, even if the
>                             kernel supports it, powerpc only
> +  --enable-fortify-source[=1|2|3]
> +                          Use -D_FORTIFY_SOURCE=[1|2|3] to control code
> +                          hardening, defaults to highest possible value
> +                          supported by the build compiler.
>   
>   Optional Packages:
>     --with-PACKAGE[=ARG]    use PACKAGE [ARG=yes]
> @@ -3717,6 +3725,18 @@ if test "$use_scv" != "no"; then :
>   
>   fi
>   
> +# Check whether --enable-fortify-source was given.
> +if test "${enable_fortify_source+set}" = set; then :
> +  enableval=$enable_fortify_source; enable_fortify_source=$enableval
> +else
> +  enable_fortify_source=no
> +fi
> +
> +case "$enable_fortify_source" in
> +1|2|3|no|yes) ;;
> +*) as_fn_error $? "Not a valid argument for --enable-fortify-source: \"$enable_fortify_source\"" "$LINENO" 5;;
> +esac
> +
>   # We keep the original values in `$config_*' and never modify them, so we
>   # can write them unchanged into config.make.  Everything else uses
>   # $machine, $vendor, and $os, and changes them whenever convenient.
> @@ -6353,40 +6373,67 @@ $as_echo "#define HAVE_LIBCAP 1" >>confdefs.h
>   fi
>   
>   
> -CPPUNDEFS=
> -{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for _FORTIFY_SOURCE predefine" >&5
> -$as_echo_n "checking for _FORTIFY_SOURCE predefine... " >&6; }
> -if ${libc_cv_predef_fortify_source+:} false; then :
> +no_fortify_source="-Wp,-U_FORTIFY_SOURCE"
> +fortify_source="${no_fortify_source}"
> +
> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for __builtin_dynamic_object_size" >&5
> +$as_echo_n "checking for __builtin_dynamic_object_size... " >&6; }
> +if ${libc_cv___builtin_dynamic_object_size+:} false; then :
>     $as_echo_n "(cached) " >&6
>   else
> -  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
> +
> +    cat confdefs.h - <<_ACEOF >conftest.$ac_ext
>   /* end confdefs.h.  */
>   
>   int
>   main ()
>   {
> -
> -#ifdef _FORTIFY_SOURCE
> -# error bogon
> -#endif
> +__builtin_dynamic_object_size("", 0)
>     ;
>     return 0;
>   }
>   _ACEOF
> -if ac_fn_c_try_compile "$LINENO"; then :
> -  libc_cv_predef_fortify_source=no
> +if ac_fn_c_try_link "$LINENO"; then :
> +  libc_cv___builtin_dynamic_object_size=yes
> +         if test "$enable_fortify_source" = yes; then :
> +  enable_fortify_source=3
> +fi
>   else
> -  libc_cv_predef_fortify_source=yes
> +  libc_cv___builtin_dynamic_object_size=no
> +         if test "$enable_fortify_source" = yes; then :
> +  enable_fortify_source=2
>   fi
> -rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
>   fi
> -{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_predef_fortify_source" >&5
> -$as_echo "$libc_cv_predef_fortify_source" >&6; }
> -if test $libc_cv_predef_fortify_source = yes; then
> -  CPPUNDEFS="${CPPUNDEFS:+$CPPUNDEFS }-U_FORTIFY_SOURCE"
> +rm -f core conftest.err conftest.$ac_objext \
> +    conftest$ac_exeext conftest.$ac_ext
> +
> +fi
> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv___builtin_dynamic_object_size" >&5
> +$as_echo "$libc_cv___builtin_dynamic_object_size" >&6; }
> +
> +case $enable_fortify_source in #(
> +  1|2) :
> +    libc_cv_fortify_source=yes ;; #(
> +  3) :
> +    if test "$libc_cv___builtin_dynamic_object_size" = yes; then :
> +  libc_cv_fortify_source=yes
> +else
> +  as_fn_error $? "Compiler doesn't provide necessary support for _FORTIFY_SOURCE=3" "$LINENO" 5
> +fi ;; #(
> +  *) :
> +    libc_cv_fortify_source=no ;;
> +esac
> +
> +if test "$libc_cv_fortify_source" = yes; then :
> +  fortify_source="${fortify_source},-D_FORTIFY_SOURCE=${enable_fortify_source}"
> +
>   fi
>   
>   
> +
> +
> +
> +
>   { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the assembler requires one version per symbol" >&5
>   $as_echo_n "checking whether the assembler requires one version per symbol... " >&6; }
>   if ${libc_cv_symver_needs_alias+:} false; then :
> diff --git a/configure.ac b/configure.ac
> index 21879c933c..860109e60a 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -466,6 +466,17 @@ AC_ARG_ENABLE([scv],
>   
>   AS_IF([[test "$use_scv" != "no"]],[AC_DEFINE(USE_PPC_SCV)])
>   
> +dnl Build glibc with _FORTIFY_SOURCE
> +AC_ARG_ENABLE(fortify-source,
> +              AS_HELP_STRING([--enable-fortify-source@<:@=1|2|3@:>@],
> +                             [Use -D_FORTIFY_SOURCE=[1|2|3] to control code hardening, defaults to highest possible value supported by the build compiler.]),
> +              [enable_fortify_source=$enableval],
> +              [enable_fortify_source=no])
> +case "$enable_fortify_source" in
> +1|2|3|no|yes) ;;
> +*) AC_MSG_ERROR([Not a valid argument for --enable-fortify-source: "$enable_fortify_source"]);;
> +esac
> +
>   # We keep the original values in `$config_*' and never modify them, so we
>   # can write them unchanged into config.make.  Everything else uses
>   # $machine, $vendor, and $os, and changes them whenever convenient.
> @@ -1559,24 +1570,37 @@ if test "x$have_selinux" = xyes; then
>   fi
>   AC_SUBST(have_selinux)
>   
> -CPPUNDEFS=
> -dnl Check for silly hacked compilers predefining _FORTIFY_SOURCE.
> -dnl Since we are building the implementations of the fortified functions here,
> -dnl having the macro defined interacts very badly.
> -dnl _FORTIFY_SOURCE requires compiler optimization level 1 (gcc -O1)
> -dnl and above (see "man FEATURE_TEST_MACROS").
> -dnl So do NOT replace AC_COMPILE_IFELSE with AC_PREPROC_IFELSE.
> -AC_CACHE_CHECK([for _FORTIFY_SOURCE predefine], libc_cv_predef_fortify_source,
> -[AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[]], [[
> -#ifdef _FORTIFY_SOURCE
> -# error bogon
> -#endif]])],
> -		[libc_cv_predef_fortify_source=no],
> -		[libc_cv_predef_fortify_source=yes])])
> -if test $libc_cv_predef_fortify_source = yes; then
> -  CPPUNDEFS="${CPPUNDEFS:+$CPPUNDEFS }-U_FORTIFY_SOURCE"
> -fi
> -AC_SUBST(CPPUNDEFS)
> +dnl Check if we support the requested _FORTIFY_SOURCE level
> +dnl If not, then don't use it.
> +dnl Note that _FORTIFY_SOURCE may have been set through FLAGS too.
> +dnl _FORTIFY_SOURCE value will be selectively disabled for function that can't
> +dnl support it
> +no_fortify_source="-Wp,-U_FORTIFY_SOURCE"
> +fortify_source="${no_fortify_source}"
> +
> +AC_CACHE_CHECK([for __builtin_dynamic_object_size], [libc_cv___builtin_dynamic_object_size], [
> +    AC_LINK_IFELSE([AC_LANG_PROGRAM([], [__builtin_dynamic_object_size("", 0)])],
> +        [libc_cv___builtin_dynamic_object_size=yes
> +         AS_IF([test "$enable_fortify_source" = yes], [enable_fortify_source=3])],
> +        [libc_cv___builtin_dynamic_object_size=no
> +         AS_IF([test "$enable_fortify_source" = yes], [enable_fortify_source=2])])
> +])
> +
> +AS_CASE([$enable_fortify_source],
> +        [1|2], [libc_cv_fortify_source=yes],
> +        [3], [AS_IF([test "$libc_cv___builtin_dynamic_object_size" = yes],
> +                    [libc_cv_fortify_source=yes],
> +                    [AC_MSG_ERROR([Compiler doesn't provide necessary support for _FORTIFY_SOURCE=3])])],
> +        [libc_cv_fortify_source=no])
> +
> +AS_IF([test "$libc_cv_fortify_source" = yes],
> +      [fortify_source="${fortify_source},-D_FORTIFY_SOURCE=${enable_fortify_source}"]
> +      )
> +
> +AC_SUBST(enable_fortify_source)
> +AC_SUBST(libc_cv_fortify_source)
> +AC_SUBST(no_fortify_source)
> +AC_SUBST(fortify_source)
>   
>   dnl Starting with binutils 2.35, GAS can attach multiple symbol versions
>   dnl to one symbol (PR 23840).
> diff --git a/elf/rtld-Rules b/elf/rtld-Rules
> index 56bc4543de..365a3408f3 100644
> --- a/elf/rtld-Rules
> +++ b/elf/rtld-Rules
> @@ -144,6 +144,6 @@ cpp-srcs-left := $(rtld-modules:%.os=%)
>   lib := rtld
>   include $(patsubst %,$(..)libof-iterator.mk,$(cpp-srcs-left))
>   
> -rtld-CFLAGS += $(no-stack-protector)
> +rtld-CFLAGS += $(no-stack-protector) $(no-fortify-source)
>   
>   endif
> diff --git a/manual/install.texi b/manual/install.texi
> index a44a552d1f..e9c66ba499 100644
> --- a/manual/install.texi
> +++ b/manual/install.texi
> @@ -303,6 +303,14 @@ Specify the URL that users should visit if they wish to report a bug,
>   to be included in @option{--help} output from programs installed with
>   @theglibc{}.  The default value refers to the main bug-reporting
>   information for @theglibc{}.
> +
> +@item --enable-fortify-source
> +@itemx --enable-fortify-source=@var{LEVEL}
> +Use -D_FORTIFY_SOURCE=@option{LEVEL} to control hardening in the GNU C Library.
> +If not provided, @option{LEVEL} defaults to highest possible value supported by
> +the build compiler.
> +
> +Default is to disable fortification.
>   @end table
>   
>   To build the library and related programs, type @code{make}.  This will
> diff --git a/scripts/build-many-glibcs.py b/scripts/build-many-glibcs.py
> index e022abe284..e4eaec01e3 100755
> --- a/scripts/build-many-glibcs.py
> +++ b/scripts/build-many-glibcs.py
> @@ -464,7 +464,9 @@ class Context(object):
>                                         {'arch': 'i486',
>                                          'ccopts': '-m32 -march=i486'},
>                                         {'arch': 'i586',
> -                                       'ccopts': '-m32 -march=i586'}])
> +                                       'ccopts': '-m32 -march=i586'},
> +                                      {'variant': 'enable-fortify-source',
> +                                       'cfg': ['--enable-fortify-source']}])
>           self.add_config(arch='x86_64',
>                           os_name='gnu',
>                           gcc_cfg=['--disable-multilib'])