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

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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.



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