Re: [PATCH] lkdtm: Fix content of section containing lkdtm_rodata_do_nothing()

On Fri, Oct 8, 2021 at 9:59 AM Christophe Leroy christophe.leroy@csgroup.eu wrote:

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")

Thanks for the patch; sorry I broke this. Reviewed-by: Nick Desaulniers ndesaulniers@google.com

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

---

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

diff --git a/drivers/misc/lkdtm/Makefile b/drivers/misc/lkdtm/Makefile index aa12097668d3..e2984ce51fe4 100644 --- a/drivers/misc/lkdtm/Makefile +++ b/drivers/misc/lkdtm/Makefile @@ -20,7 +20,7 @@ CFLAGS_REMOVE_rodata.o += $(CC_FLAGS_LTO)

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) -- 2.31.1