[PATCH v5 4/5] Add --disable-default-dt-relr

H.J. Lu hjl.tools@gmail.com
Thu Mar 3 04:50:25 GMT 2022


Enable DT_RELR in glibc shared libraries and position independent
executables (PIE) automatically if linker supports -z pack-relative-relocs.

Also add a new configuration option, --disable-default-dt-relr, to
avoid DT_RELR usage in glibc shared libraries and PIEs.
---
 INSTALL             |  6 ++++++
 Makeconfig          | 19 +++++++++++++++++++
 Makerules           |  2 ++
 configure           | 18 ++++++++++++++++++
 configure.ac        | 13 +++++++++++++
 elf/Makefile        |  4 +++-
 manual/install.texi |  5 +++++
 7 files changed, 66 insertions(+), 1 deletion(-)

diff --git a/INSTALL b/INSTALL
index 63c022d6b9..4a6506f11f 100644
--- a/INSTALL
+++ b/INSTALL
@@ -133,6 +133,12 @@ if 'CFLAGS' is specified it must enable optimization.  For example:
      used with the GCC option, -static-pie, which is available with GCC
      8 or above, to create static PIE.
 
+'--disable-default-dt-relr'
+     Don't enable DT_RELR in glibc shared libraries and position
+     independent executables (PIE). By default, DT_RELR is enabled in
+     glibc shared libraries and position independent executables on
+     targets that support it.
+
 '--enable-cet'
 '--enable-cet=permissive'
      Enable Intel Control-flow Enforcement Technology (CET) support.
diff --git a/Makeconfig b/Makeconfig
index 47db08d6ae..70c0acc065 100644
--- a/Makeconfig
+++ b/Makeconfig
@@ -358,6 +358,23 @@ else
 real-static-start-installed-name = $(static-start-installed-name)
 endif
 
+# Linker option to enable and disable DT-RELR.
+ifeq ($(have-dt-relr),yes)
+dt-relr-ldflag = -Wl,-z,pack-relative-relocs
+no-dt-relr-ldflag = -Wl,-z,nopack-relative-relocs
+else
+dt-relr-ldflag =
+no-dt-relr-ldflag =
+endif
+
+# Default linker option for DT-RELR.
+ifeq (yes,$(build-dt-relr-default))
+default-rt-relr-ldflag = $(dt-relr-ldflag)
+else
+default-rt-relr-ldflag = $(no-dt-relr-ldflag)
+endif
+LDFLAGS-rtld += $(default-rt-relr-ldflag)
+
 ifeq (yesyes,$(build-shared)$(have-z-combreloc))
 combreloc-LDFLAGS = -Wl,-z,combreloc
 LDFLAGS.so += $(combreloc-LDFLAGS)
@@ -419,6 +436,7 @@ link-extra-libs-tests = $(libsupport)
 # Command for linking PIE programs with the C library.
 ifndef +link-pie
 +link-pie-before-inputs = $(if $($(@F)-no-pie),$(no-pie-ldflag),-pie) \
+	     $(if $($(@F)-no-dt-relr),$(no-dt-relr-ldflag),$(default-rt-relr-ldflag)) \
 	     -Wl,-O1 -nostdlib -nostartfiles \
 	     $(sysdep-LDFLAGS) $(LDFLAGS) $(LDFLAGS-$(@F)) \
 	     $(combreloc-LDFLAGS) $(relro-LDFLAGS) $(hashstyle-LDFLAGS) \
@@ -451,6 +469,7 @@ endif
 ifndef +link-static
 +link-static-before-inputs = -nostdlib -nostartfiles -static \
 	      $(if $($(@F)-no-pie),$(no-pie-ldflag),$(static-pie-ldflag)) \
+	      $(if $($(@F)-no-dt-relr),$(no-dt-relr-ldflag),$(default-rt-relr-ldflag)) \
 	      $(sysdep-LDFLAGS) $(LDFLAGS) $(LDFLAGS-$(@F))  \
 	      $(firstword $(CRT-$(@F)) $(csu-objpfx)$(real-static-start-installed-name)) \
 	      $(+preinit) $(+prectorT)
diff --git a/Makerules b/Makerules
index 428464f092..7c1da551bf 100644
--- a/Makerules
+++ b/Makerules
@@ -536,6 +536,7 @@ lib%.so: lib%_pic.a $(+preinit) $(+postinit) $(link-libc-deps)
 define build-shlib-helper
 $(LINK.o) -shared -static-libgcc -Wl,-O1 $(sysdep-LDFLAGS) \
 	  $(if $($(@F)-no-z-defs)$(no-z-defs),,-Wl,-z,defs) $(rtld-LDFLAGS) \
+	  $(if $($(@F)-no-dt-relr),$(no-dt-relr-ldflag),$(default-rt-relr-ldflag)) \
 	  $(extra-B-$(@F:lib%.so=%).so) -B$(csu-objpfx) \
 	  $(extra-B-$(@F:lib%.so=%).so) $(load-map-file) \
 	  -Wl,-soname=lib$(libprefix)$(@F:lib%.so=%).so$($(@F)-version) \
@@ -595,6 +596,7 @@ endef
 define build-module-helper
 $(LINK.o) -shared -static-libgcc $(sysdep-LDFLAGS) $(rtld-LDFLAGS) \
 	  $(if $($(@F)-no-z-defs)$(no-z-defs),,-Wl,-z,defs) \
+	  $(if $($(@F)-no-dt-relr),$(no-dt-relr-ldflag),$(default-rt-relr-ldflag)) \
 	  -B$(csu-objpfx) $(load-map-file) \
 	  $(LDFLAGS.so) $(LDFLAGS-$(@F:%.so=%).so) \
 	  $(link-test-modules-rpath-link) \
diff --git a/configure b/configure
index 9156e29fe9..ee4137a977 100755
--- a/configure
+++ b/configure
@@ -768,6 +768,7 @@ enable_sanity_checks
 enable_shared
 enable_profile
 enable_default_pie
+enable_default_dt_relr
 enable_timezone_tools
 enable_hardcoded_path_in_tests
 enable_hidden_plt
@@ -1425,6 +1426,7 @@ Optional Features:
   --enable-profile        build profiled library [default=no]
   --disable-default-pie   Do not build glibc programs and the testsuite as PIE
                           [default=no]
+  --disable-dt-relr       Do not enable DT_RELR in glibc[default=no]
   --disable-timezone-tools
                           do not install timezone tools [default=install]
   --enable-hardcoded-path-in-tests
@@ -3441,6 +3443,13 @@ else
   default_pie=yes
 fi
 
+# Check whether --enable-default-dt-relr was given.
+if test "${enable_default_dt_relr+set}" = set; then :
+  enableval=$enable_default_dt_relr; default_dt_relr=$enableval
+else
+  default_dt_relr=yes
+fi
+
 # Check whether --enable-timezone-tools was given.
 if test "${enable_timezone_tools+set}" = set; then :
   enableval=$enable_timezone_tools; enable_timezone_tools=$enableval
@@ -7136,6 +7145,15 @@ fi
 config_vars="$config_vars
 enable-static-pie = $libc_cv_static_pie"
 
+# Disable build-dt-relr-default if linker does not support it or glibc is
+# configured with --disable-default-dt-relr.
+build_dt_relr_default=$default_dt_relr
+if test "x$build_dt_relr_default" != xno; then
+  build_dt_relr_default=$libc_cv_dt_relr
+fi
+config_vars="$config_vars
+build-dt-relr-default = $build_dt_relr_default"
+
 # Set the `multidir' variable by grabbing the variable from the compiler.
 # We do it once and save the result in a generated makefile.
 libc_cv_multidir=`${CC-cc} $CFLAGS $CPPFLAGS -print-multi-directory`
diff --git a/configure.ac b/configure.ac
index 5c09871fee..680b036ffa 100644
--- a/configure.ac
+++ b/configure.ac
@@ -197,6 +197,11 @@ AC_ARG_ENABLE([default-pie],
 			     [Do not build glibc programs and the testsuite as PIE @<:@default=no@:>@]),
 	      [default_pie=$enableval],
 	      [default_pie=yes])
+AC_ARG_ENABLE([default-dt-relr],
+	      AS_HELP_STRING([--disable-dt-relr],
+			     [Do not enable DT_RELR in glibc@<:@default=no@:>@]),
+	      [default_dt_relr=$enableval],
+	      [default_dt_relr=yes])
 AC_ARG_ENABLE([timezone-tools],
 	      AS_HELP_STRING([--disable-timezone-tools],
 			     [do not install timezone tools @<:@default=install@:>@]),
@@ -1914,6 +1919,14 @@ if test "$libc_cv_static_pie" = "yes"; then
 fi
 LIBC_CONFIG_VAR([enable-static-pie], [$libc_cv_static_pie])
 
+# Disable build-dt-relr-default if linker does not support it or glibc is
+# configured with --disable-default-dt-relr.
+build_dt_relr_default=$default_dt_relr
+if test "x$build_dt_relr_default" != xno; then
+  build_dt_relr_default=$libc_cv_dt_relr
+fi
+LIBC_CONFIG_VAR([build-dt-relr-default], [$build_dt_relr_default])
+
 # Set the `multidir' variable by grabbing the variable from the compiler.
 # We do it once and save the result in a generated makefile.
 libc_cv_multidir=`${CC-cc} $CFLAGS $CPPFLAGS -print-multi-directory`
diff --git a/elf/Makefile b/elf/Makefile
index d3118b9777..c4384536ba 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -1567,6 +1567,7 @@ $(objpfx)nodlopen2.out: $(objpfx)nodlopenmod2.so
 
 $(objpfx)filtmod1.so: $(objpfx)filtmod1.os $(objpfx)filtmod2.so
 	$(LINK.o) -shared -o $@ -B$(csu-objpfx) $(LDFLAGS.so) \
+		  $(default-rt-relr-ldflag) \
 		  -L$(subst :, -L,$(rpath-link)) \
 		  -Wl,-rpath-link=$(rpath-link) \
 		  $< -Wl,-F,$(objpfx)filtmod2.so
@@ -2366,7 +2367,7 @@ $(objpfx)tst-big-note: $(objpfx)tst-big-note-lib.so
 # artificial, large note in tst-big-note-lib.o and invalidate the
 # test.
 $(objpfx)tst-big-note-lib.so: $(objpfx)tst-big-note-lib.o
-	$(LINK.o) -shared -o $@ $(LDFLAGS.so) $<
+	$(LINK.o) -shared -o $@ $(LDFLAGS.so) $(default-rt-relr-ldflag) $<
 
 $(objpfx)tst-unwind-ctor: $(objpfx)tst-unwind-ctor-lib.so
 
@@ -2672,6 +2673,7 @@ $(objpfx)tst-ro-dynamic: $(objpfx)tst-ro-dynamic-mod.so
 $(objpfx)tst-ro-dynamic-mod.so: $(objpfx)tst-ro-dynamic-mod.os \
   tst-ro-dynamic-mod.map
 	$(LINK.o) -nostdlib -nostartfiles -shared -o $@ \
+		$(default-rt-relr-ldflag) \
 		-Wl,--script=tst-ro-dynamic-mod.map \
 		$(objpfx)tst-ro-dynamic-mod.os
 
diff --git a/manual/install.texi b/manual/install.texi
index 29c52f2927..04ea996561 100644
--- a/manual/install.texi
+++ b/manual/install.texi
@@ -161,6 +161,11 @@ and architecture support it, static executables are built as static PIE and the
 resulting glibc can be used with the GCC option, -static-pie, which is
 available with GCC 8 or above, to create static PIE.
 
+@item --disable-default-dt-relr
+Don't enable DT_RELR in glibc shared libraries and position independent
+executables (PIE).  By default, DT_RELR is enabled in glibc shared
+libraries and position independent executables on targets that support it.
+
 @item --enable-cet
 @itemx --enable-cet=permissive
 Enable Intel Control-flow Enforcement Technology (CET) support.  When
-- 
2.35.1



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