linux-kernel - [PATCH] [Rebased for 4.14] lkdtm: Fix content of section containing lkdtm_rodata_do

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Date:   Sun, 30 Jan 2022 09:55:39 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
CC:     Christophe Leroy <christophe.leroy@...roup.eu>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        Arnd Bergmann <arnd@...db.de>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>
Subject: [PATCH] [Rebased for 4.14] lkdtm: Fix content of section containing
 lkdtm_rodata_do_nothing()

This is backport for 4.14

(cherry picked from commit bc93a22a19eb2b68a16ecf04cdf4b2ed65aaf398)

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
---
 drivers/misc/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
index 76f6a4f628b3..cc0df7280fe5 100644
--- a/drivers/misc/Makefile
+++ b/drivers/misc/Makefile
@@ -69,7 +69,7 @@ KCOV_INSTRUMENT_lkdtm_rodata.o	:= n
 
 OBJCOPYFLAGS :=
 OBJCOPYFLAGS_lkdtm_rodata_objcopy.o := \
-	--rename-section .text=.rodata,alloc,readonly,load
+	--rename-section .text=.rodata,alloc,readonly,load,contents
 targets += lkdtm_rodata.o lkdtm_rodata_objcopy.o
 $(obj)/lkdtm_rodata_objcopy.o: $(obj)/lkdtm_rodata.o FORCE
 	$(call if_changed,objcopy)
-- 
2.33.1