[PATCH 5.4 025/320] lkdtm: Fix content of section containing lkdtm_rodata_do_nothing()

Greg Kroah-Hartman
2022-01-24T19:28:06Z

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

--- a/drivers/misc/lkdtm/Makefile
+++ b/drivers/misc/lkdtm/Makefile
@@ -16,7 +16,7 @@ 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)