[PATCH] uml: fix compilation and execution with hardened GCC
To make some half-assembly stubs compile, disable various "hardened" GCC features: *) we can't make it build PIC code as we need %ebx to do syscalls and GCC wants it free for PIC *) we can't leave stack protection as the stub is moved (not relocated!) in memory so the RIP-relative access to the canary tries reading from an unmapped address and causes a segfault, since we move the stub of various megabytes (the exact amount will be decided at runtime) away from the link-time address. Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it> Acked-by: Jeff Dike <jdike@addtoit.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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4 changed files with 17 additions and 2 deletions
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@ -118,6 +118,10 @@ prepare: $(ARCH_DIR)/include/kern_constants.h
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LINK-$(CONFIG_LD_SCRIPT_STATIC) += -static
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LINK-$(CONFIG_LD_SCRIPT_DYN) += -Wl,-rpath,/lib
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CFLAGS_NO_HARDENING := $(call cc-option, -fno-PIC,) $(call cc-option, -fno-pic,) \
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$(call cc-option, -fno-stack-protector,) \
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$(call cc-option, -fno-stack-protector-all,)
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CPP_MODE-$(CONFIG_MODE_TT) := -DMODE_TT
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CONFIG_KERNEL_STACK_ORDER ?= 2
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STACK_SIZE := $(shell echo $$[ 4096 * (1 << $(CONFIG_KERNEL_STACK_ORDER)) ] )
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@ -227,4 +231,4 @@ $(ARCH_DIR)/include/kern_constants.h: $(objtree)/$(ARCH_DIR)/include
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@echo ' SYMLINK $@'
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$(Q)ln -sf ../../../include/asm-um/asm-offsets.h $@
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export SUBARCH USER_CFLAGS OS
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export SUBARCH USER_CFLAGS CFLAGS_NO_HARDENING OS
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@ -11,4 +11,11 @@ USER_OBJS := clone.o
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include arch/um/scripts/Makefile.rules
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# clone.o is in the stub, so it can't be built with profiling
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$(obj)/clone.o : c_flags = -Wp,-MD,$(depfile) $(call unprofile,$(USER_CFLAGS))
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# GCC hardened also auto-enables -fpic, but we need %ebx so it can't work ->
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# disable it
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CFLAGS_clone.o := $(CFLAGS_NO_HARDENING)
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# since we're setting c_flags we _must_ add $(CFLAGS_$(*F).o).
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$(obj)/clone.o : c_flags = -Wp,-MD,$(depfile) $(call unprofile,$(USER_CFLAGS)) $(CFLAGS_$(*F).o)
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@ -13,6 +13,8 @@ USER_OBJS := bugs.o ptrace_user.o sigcontext.o fault.o stub_segv.o
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USER_OBJS += user-offsets.s
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extra-y += user-offsets.s
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CFLAGS_stub_segv.o := $(CFLAGS_NO_HARDENING)
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extra-$(CONFIG_MODE_TT) += unmap.o
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include arch/um/scripts/Makefile.rules
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@ -21,6 +21,8 @@ USER_OBJS := ptrace_user.o sigcontext.o stub_segv.o
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USER_OBJS += user-offsets.s
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extra-y += user-offsets.s
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CFLAGS_stub_segv.o := $(CFLAGS_NO_HARDENING)
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extra-$(CONFIG_MODE_TT) += unmap.o
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include arch/um/scripts/Makefile.rules
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