linux-kernel - [PATCH 5.16 0059/1039] lkdtm: Fix content of section containing lkdtm_rodata_do

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Message-Id: <20220124184127.128262775@linuxfoundation.org>
Date:   Mon, 24 Jan 2022 19:30:48 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        Arnd Bergmann <arnd@...db.de>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>
Subject: [PATCH 5.16 0059/1039] lkdtm: Fix content of section containing lkdtm_rodata_do_nothing()

From: Christophe Leroy <christophe.leroy@...roup.eu>

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@...r.kernel.org
Cc: Kees Cook <keescook@...omium.org>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: Nathan Chancellor <nathan@...nel.org>
Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
Signed-off-by: Kees Cook <keescook@...omium.org>
Link: https://lore.kernel.org/r/8900731fbc05fb8b0de18af7133a8fc07c3c53a1.1633712176.git.christophe.leroy@csgroup.eu
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/misc/lkdtm/Makefile |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/misc/lkdtm/Makefile
+++ b/drivers/misc/lkdtm/Makefile
@@ -20,7 +20,7 @@ CFLAGS_REMOVE_rodata.o		+= $(CC_FLAGS_LT
 
 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)