From 8b8f13b60d9587e91e8719239a9249b448bc1307 Mon Sep 17 00:00:00 2001 From: Siddhesh Poyarekar Date: Mon, 15 Mar 2021 20:25:00 +0530 Subject: Build libc-start with stack protector for SHARED This does not change the emitted code since __libc_start_main does not return, but is important for formal flags compliance. This also cleans up the cosmetic inconsistency in the stack protector flags in csu, especially the incorrect value of STACK_PROTECTOR_LEVEL. Reviewed-by: Adhemerval Zanella --- Makeconfig | 8 ++++++++ csu/Makefile | 22 ++++++++++++---------- elf/Makefile | 4 ---- 3 files changed, 20 insertions(+), 14 deletions(-) diff --git a/Makeconfig b/Makeconfig index 0a4811b..01f8638 100644 --- a/Makeconfig +++ b/Makeconfig @@ -856,6 +856,14 @@ ifneq ($(stack-protector),) +stack-protector=$(stack-protector) endif +# Some routines are unsafe to build with stack-protection since they're called +# before the stack check guard is set up. Provide a way to disable stack +# protector. The first argument is the extension (.o, .os, .oS) and the second +# is a list of routines that this path should be applied to. +define elide-stack-protector +$(if $(filter $(@F),$(patsubst %,%$(1),$(2))), $(no-stack-protector)) +endef + # This is the program that generates makefile dependencies from C source files. # The -MP flag tells GCC >= 3.2 (which we now require) to produce dummy # targets for headers so that removed headers don't break the build. diff --git a/csu/Makefile b/csu/Makefile index e587434..3054329 100644 --- a/csu/Makefile +++ b/csu/Makefile @@ -45,18 +45,20 @@ install-lib = $(start-installed-name) g$(start-installed-name) $(csu-dummies) # code is compiled with special flags. tests = -CFLAGS-.o += $(no-stack-protector) -CFLAGS-.op += $(no-stack-protector) -CFLAGS-.os += $(no-stack-protector) - -# Dummy object not actually used for anything. It is linked into -# crt1.o nevertheless, which in turn is statically linked into +# static-reloc.os is a dummy object not actually used for anything. It is +# linked into crt1.o nevertheless, which in turn is statically linked into # applications, so that build flags matter. # See . -# NB: Using $(stack-protector) in this way causes a wrong definition -# STACK_PROTECTOR_LEVEL due to the preceding $(no-stack-protector), -# but it does not matter for this source file. -CFLAGS-static-reloc.os += $(stack-protector) +# +# libc-start.os is safe to be built with stack protector since +# __libc_start_main is called after stack canary setup is done. +ssp-safe.os = static-reloc libc-start + +CFLAGS-.o += $(call elide-stack-protector,.o,$(routines)) +CFLAGS-.op += $(call elide-stack-protector,.op,$(routines)) +CFLAGS-.oS += $(call elide-stack-protector,.oS,$(routines)) +CFLAGS-.os += $(call elide-stack-protector,.os,$(filter-out \ + $(ssp-safe.os),$(routines))) ifeq (yes,$(build-shared)) extra-objs += S$(start-installed-name) gmon-start.os diff --git a/elf/Makefile b/elf/Makefile index ba4689a..3b8e13e 100644 --- a/elf/Makefile +++ b/elf/Makefile @@ -83,10 +83,6 @@ endif # Also compile all routines in the static library that are elided from # the shared libc because they are in libc.a in the same way. -define elide-stack-protector -$(if $(filter $(@F),$(patsubst %,%$(1),$(2))), $(no-stack-protector)) -endef - CFLAGS-.o += $(call elide-stack-protector,.o,$(elide-routines.os)) CFLAGS-.op += $(call elide-stack-protector,.op,$(elide-routines.os)) CFLAGS-.os += $(call elide-stack-protector,.os,$(all-rtld-routines)) -- cgit v1.1