[PATCH 4.19 041/239] lkdtm: Fix content of section containing lkdtm_rodata_do_nothing()

[Greg Kroah-Hartman]

From: Christophe Leroy <christophe.leroy@xxxxxxxxxx>

commit bc93a22a19eb2b68a16ecf04cdf4b2ed65aaf398 upstream.

On a kernel without CONFIG_STRICT_KERNEL_RWX, running EXEC_RODATA
test leads to "Illegal instruction" failure.

Looking at the content of rodata_objcopy.o, we see that the
function content zeroes only:

	Disassembly of section .rodata:

	0000000000000000 <.lkdtm_rodata_do_nothing>:
	   0:	00 00 00 00 	.long 0x0

Add the contents flag in order to keep the content of the section
while renaming it.

	Disassembly of section .rodata:

	0000000000000000 <.lkdtm_rodata_do_nothing>:
	   0:	4e 80 00 20 	blr

Fixes: e9e08a07385e ("lkdtm: support llvm-objcopy")
Cc: stable@xxxxxxxxxxxxxxx
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Cc: Nathan Chancellor <nathan@xxxxxxxxxx>
Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Link: https://lore.kernel.org/r/8900731fbc05fb8b0de18af7133a8fc07c3c53a1.1633712176.git.christophe.leroy@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/misc/lkdtm/Makefile |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/misc/lkdtm/Makefile
+++ b/drivers/misc/lkdtm/Makefile
@@ -13,7 +13,7 @@ KCOV_INSTRUMENT_rodata.o	:= n
 
 OBJCOPYFLAGS :=
 OBJCOPYFLAGS_rodata_objcopy.o	:= \
-			--rename-section .noinstr.text=.rodata,alloc,readonly,load
+			--rename-section .noinstr.text=.rodata,alloc,readonly,load,contents
 targets += rodata.o rodata_objcopy.o
 $(obj)/rodata_objcopy.o: $(obj)/rodata.o FORCE
 	$(call if_changed,objcopy)