Re: [PATCH 4.14 114/165] x86/vdso: Fix vDSO build if a retpoline is emitted

[Nikola Ciprich]

Hi Greg and others,

sorry for reporting this so late, but still...

this breaks build on older compilers, since it requires
-mindirect-branch=thunk-inline -mindirect-branch-register even though
retpoline support is disabled in kernel config.. is this expected?

BR

nik


On Mon, Sep 03, 2018 at 06:56:40PM +0200, Greg Kroah-Hartman wrote:
> 4.14-stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Andy Lutomirski <luto@xxxxxxxxxx>
> 
> commit 2e549b2ee0e358bc758480e716b881f9cabedb6a upstream.
> 
> Currently, if the vDSO ends up containing an indirect branch or
> call, GCC will emit the "external thunk" style of retpoline, and it
> will fail to link.
> 
> Fix it by building the vDSO with inline retpoline thunks.
> 
> I haven't seen any reports of this triggering on an unpatched
> kernel.
> 
> Fixes: commit 76b043848fd2 ("x86/retpoline: Add initial retpoline support")
> Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Acked-by: Matt Rickard <matt@xxxxxxxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc: Jason Vas Dias <jason.vas.dias@xxxxxxxxx>
> Cc: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Link: https://lkml.kernel.org/r/c76538cd3afbe19c6246c2d1715bc6a60bd63985.1534448381.git.luto@xxxxxxxxxx
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> 
> ---
>  Makefile                     |    4 ++++
>  arch/x86/entry/vdso/Makefile |    6 ++++--
>  2 files changed, 8 insertions(+), 2 deletions(-)
> 
> --- a/Makefile
> +++ b/Makefile
> @@ -490,9 +490,13 @@ KBUILD_AFLAGS += $(CLANG_TARGET) $(CLANG
>  endif
>  
>  RETPOLINE_CFLAGS_GCC := -mindirect-branch=thunk-extern -mindirect-branch-register
> +RETPOLINE_VDSO_CFLAGS_GCC := -mindirect-branch=thunk-inline -mindirect-branch-register
>  RETPOLINE_CFLAGS_CLANG := -mretpoline-external-thunk
> +RETPOLINE_VDSO_CFLAGS_CLANG := -mretpoline
>  RETPOLINE_CFLAGS := $(call cc-option,$(RETPOLINE_CFLAGS_GCC),$(call cc-option,$(RETPOLINE_CFLAGS_CLANG)))
> +RETPOLINE_VDSO_CFLAGS := $(call cc-option,$(RETPOLINE_VDSO_CFLAGS_GCC),$(call cc-option,$(RETPOLINE_VDSO_CFLAGS_CLANG)))
>  export RETPOLINE_CFLAGS
> +export RETPOLINE_VDSO_CFLAGS
>  
>  ifeq ($(config-targets),1)
>  # ===========================================================================
> --- a/arch/x86/entry/vdso/Makefile
> +++ b/arch/x86/entry/vdso/Makefile
> @@ -74,9 +74,9 @@ $(obj)/vdso-image-%.c: $(obj)/vdso%.so.d
>  CFL := $(PROFILING) -mcmodel=small -fPIC -O2 -fasynchronous-unwind-tables -m64 \
>         $(filter -g%,$(KBUILD_CFLAGS)) $(call cc-option, -fno-stack-protector) \
>         -fno-omit-frame-pointer -foptimize-sibling-calls \
> -       -DDISABLE_BRANCH_PROFILING -DBUILD_VDSO
> +       -DDISABLE_BRANCH_PROFILING -DBUILD_VDSO $(RETPOLINE_VDSO_CFLAGS)
>  
> -$(vobjs): KBUILD_CFLAGS := $(filter-out $(GCC_PLUGINS_CFLAGS),$(KBUILD_CFLAGS)) $(CFL)
> +$(vobjs): KBUILD_CFLAGS := $(filter-out $(GCC_PLUGINS_CFLAGS) $(RETPOLINE_CFLAGS),$(KBUILD_CFLAGS)) $(CFL)
>  
>  #
>  # vDSO code runs in userspace and -pg doesn't help with profiling anyway.
> @@ -147,11 +147,13 @@ KBUILD_CFLAGS_32 := $(filter-out -mcmode
>  KBUILD_CFLAGS_32 := $(filter-out -fno-pic,$(KBUILD_CFLAGS_32))
>  KBUILD_CFLAGS_32 := $(filter-out -mfentry,$(KBUILD_CFLAGS_32))
>  KBUILD_CFLAGS_32 := $(filter-out $(GCC_PLUGINS_CFLAGS),$(KBUILD_CFLAGS_32))
> +KBUILD_CFLAGS_32 := $(filter-out $(RETPOLINE_CFLAGS),$(KBUILD_CFLAGS_32))
>  KBUILD_CFLAGS_32 += -m32 -msoft-float -mregparm=0 -fpic
>  KBUILD_CFLAGS_32 += $(call cc-option, -fno-stack-protector)
>  KBUILD_CFLAGS_32 += $(call cc-option, -foptimize-sibling-calls)
>  KBUILD_CFLAGS_32 += -fno-omit-frame-pointer
>  KBUILD_CFLAGS_32 += -DDISABLE_BRANCH_PROFILING
> +KBUILD_CFLAGS_32 += $(RETPOLINE_VDSO_CFLAGS)
>  $(obj)/vdso32.so.dbg: KBUILD_CFLAGS = $(KBUILD_CFLAGS_32)
>  
>  $(obj)/vdso32.so.dbg: FORCE \
> 
> 

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