Re: [PATCH v4 07/26] x86/build: Check W^X of vmlinux during build

[Evgeniy Baskov]

On 2023-03-08 12:34, Ard Biesheuvel wrote:
> On Thu, 15 Dec 2022 at 13:38, Evgeniy Baskov <baskov@xxxxxxxxx> wrote:
> > Check if there are simultaneously writable and executable
> > program segments in vmlinux ELF image and fail build if there are any.
> >
> > This would prevent accidental introduction of RWX segments.
> >
> > Tested-by: Mario Limonciello <mario.limonciello@xxxxxxx>
> > Tested-by: Peter Jones <pjones@xxxxxxxxxx>
> > Signed-off-by: Evgeniy Baskov <baskov@xxxxxxxxx>
> > ---
> >  arch/x86/boot/compressed/Makefile | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/arch/x86/boot/compressed/Makefile 
> > b/arch/x86/boot/compressed/Makefile
> > index 1acff356d97a..4dcab38f5a38 100644
> > --- a/arch/x86/boot/compressed/Makefile
> > +++ b/arch/x86/boot/compressed/Makefile
> > @@ -112,11 +112,17 @@ vmlinux-objs-$(CONFIG_EFI) += $(obj)/efi.o
> >  vmlinux-objs-$(CONFIG_EFI_MIXED) += $(obj)/efi_mixed.o
> >  vmlinux-objs-$(CONFIG_EFI_STUB) += 
> > $(objtree)/drivers/firmware/efi/libstub/lib.a
> >
> > +quiet_cmd_wx_check = WXCHK   $<
> > +cmd_wx_check = if $(OBJDUMP) -p $< | grep "flags .wx" > /dev/null; \
> > +              then (echo >&2 "$<: Simultaneously writable and 
> > executable sections are prohibited"; \
> > +                    /bin/false); fi
> > +
> >  $(obj)/vmlinux: $(vmlinux-objs-y) FORCE
> >         $(call if_changed,ld)
> >
> >  OBJCOPYFLAGS_vmlinux.bin :=  -R .comment -S
> >  $(obj)/vmlinux.bin: vmlinux FORCE
> > +       $(call cmd,wx_check)
>
> This breaks the way we track dependencies between make targets: the
> FORCE will result in the check being performed every time, even if
> nothing gets rebuilt.
>
> Better to do something like the below (apologies for the alphabet soup)
>
>
> --- a/arch/x86/boot/compressed/Makefile
> +++ b/arch/x86/boot/compressed/Makefile
> @@ -112,18 +112,17 @@ vmlinux-objs-$(CONFIG_EFI) += $(obj)/efi.o
>  vmlinux-objs-$(CONFIG_EFI_MIXED) += $(obj)/efi_mixed.o
>  vmlinux-objs-$(CONFIG_EFI_STUB) +=
> $(objtree)/drivers/firmware/efi/libstub/lib.a
>
> -quiet_cmd_wx_check = WXCHK   $<
> -cmd_wx_check = if $(OBJDUMP) -p $< | grep "flags .wx" > /dev/null; \
> -              then (echo >&2 "$<: Simultaneously writable and
> executable sections are prohibited"; \
> -                    /bin/false); fi
> +quiet_cmd_objcopy_and_wx_check = $(quiet_cmd_objcopy)
> +      cmd_objcopy_and_wx_check = if $(OBJDUMP) -p $< | grep "flags
> .wx" > /dev/null; then \
> +                                       (echo >&2 "$<: Simultaneously
> writable and executable sections are prohibited"; \
> +                                       /bin/false); else 
> $(cmd_objcopy); fi
>
>  $(obj)/vmlinux: $(vmlinux-objs-y) FORCE
>         $(call if_changed,ld)
>
>  OBJCOPYFLAGS_vmlinux.bin :=  -R .comment -S
>  $(obj)/vmlinux.bin: vmlinux FORCE
> -       $(call cmd,wx_check)
> -       $(call if_changed,objcopy)
> +       $(call if_changed,objcopy_and_wx_check)

Thank you for suggestion! I will fix it.