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SubjectRe: [PATCH v4 07/26] x86/build: Check W^X of vmlinux during build
On 2023-03-08 12:34, Ard Biesheuvel wrote:
> On Thu, 15 Dec 2022 at 13:38, Evgeniy Baskov <baskov@ispras.ru> 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@amd.com>
>> Tested-by: Peter Jones <pjones@redhat.com>
>> Signed-off-by: Evgeniy Baskov <baskov@ispras.ru>
>> ---
>> 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.

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