libc/glibc: add fortify option

By default, recent versions of glibc and eglibc will build some
functions that take format strings (eg. printf, syslog...) with
run-time checks against some format string attacks. This is
called a fortified build.

Unfortunately, this fails somehow while building the instrumented
version of syslog, with some kind of circular dependency...

Disable fortified builds by default, and hide the enabling option
behind EXPERIMENTAL for daring users...

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

2 files changed, 29 insertions, 1 deletions

diff --git a/config/libc/glibc-eglibc.in-common b/config/libc/glibc-eglibc.in-common
index a901e58..6e00688 100644
--- a/config/libc/glibc-eglibc.in-common
+++ b/config/libc/glibc-eglibc.in-common
@@ -58,6 +58,27 @@ config LIBC_EXTRA_CC_ARGS
       Seldom used, except for sparc64 which seems to need the flag -64
       to be passed onto gcc.
 
+config LIBC_ENABLE_FORTIFIED_BUILD
+    bool
+    prompt "Enable fortified build (EXPERIMENTAL)"
+    depends on EXPERIMENTAL
+    default n
+    help
+      If you say 'y' here, then glibc will be using fortified versions
+      of functions with format arguments (eg. vsyslog, printf...), and
+      do a sanity check on the format at runtime, to avoid some of the
+      common format string attacks.
+      
+      This is currently not supported, and will most probably result in
+      a broken build, with an error message like:
+        ../misc/syslog.c: In function '__vsyslog_chk':
+        ../misc/syslog.c:123: sorry, unimplemented: inlining failed in
+        call to 'syslog': function body not available
+      
+      If you are brave enough and want to debug the issue, then say 'y'
+      here. Otherwise, be still and say 'n' (the default). ;-)
+
+
 config LIBC_DISABLE_VERSIONING
     bool
     prompt "Disable symbols versioning"
diff --git a/scripts/build/libc/glibc-eglibc.sh-common b/scripts/build/libc/glibc-eglibc.sh-common
index c03fa11..8ec8e8d 100644
--- a/scripts/build/libc/glibc-eglibc.sh-common
+++ b/scripts/build/libc/glibc-eglibc.sh-common
@@ -114,6 +114,7 @@ do_libc() {
     local extra_cc_args
     local -a extra_config
     local -a extra_make_args
+    local glibc_cflags
 
     CT_DoStep INFO "Installing C library"
 
@@ -199,6 +200,12 @@ do_libc() {
     CT_DoLog DEBUG "Extra config args passed: '${extra_config[*]}'"
     CT_DoLog DEBUG "Extra CC args passed    : '${extra_cc_args}'"
 
+    glibc_cflags="${CT_TARGET_CFLAGS} ${CT_LIBC_GLIBC_EXTRA_CFLAGS} ${OPTIMIZE}"
+    case "${CT_LIBC_ENABLE_FORTIFIED_BUILD}" in
+        y)  ;;
+        *)  glibc_cflags+=" -U_FORTIFY_SOURCE";;
+    esac
+
     # ./configure is mislead by our tools override wrapper for bash
     # so just tell it where the real bash is _on_the_target_!
     # Notes:
@@ -221,7 +228,7 @@ do_libc() {
     # Set BUILD_CC, or we won't be able to build datafiles
 
     BUILD_CC="${CT_BUILD}-gcc"                                      \
-    CFLAGS="${CT_TARGET_CFLAGS} ${CT_LIBC_GLIBC_EXTRA_CFLAGS} ${OPTIMIZE}"  \
+    CFLAGS="${glibc_cflags}"                                        \
     CC="${CT_TARGET}-gcc ${CT_LIBC_EXTRA_CC_ARGS} ${extra_cc_args}" \
     AR=${CT_TARGET}-ar                                              \
     RANLIB=${CT_TARGET}-ranlib                                      \