[4.14 PATCH] lkdtm: support llvm-objcopy

[4.14 PATCH] lkdtm: support llvm-objcopy

[Nick Desaulniers]

commit e9e08a07385e08f1a7f85c5d1e345c21c9564963 upstream.

With CONFIG_LKDTM=y and make OBJCOPY=llvm-objcopy, llvm-objcopy errors:
llvm-objcopy: error: --set-section-flags=.text conflicts with
--rename-section=.text=.rodata

Rather than support setting flags then renaming sections vs renaming
then setting flags, it's simpler to just change both at the same time
via --rename-section. Adding the load flag is required for GNU objcopy
to mark .rodata Type as PROGBITS after the rename.

This can be verified with:
$ readelf -S drivers/misc/lkdtm/rodata_objcopy.o
...
Section Headers:
  [Nr] Name              Type             Address           Offset
       Size              EntSize          Flags  Link  Info  Align
...
  [ 1] .rodata           PROGBITS         0000000000000000  00000040
       0000000000000004  0000000000000000   A       0     0     4
...

Which shows that .text is now renamed .rodata, the alloc flag A is set,
the type is PROGBITS, and the section is not flagged as writeable W.

Cc: stable@vger.kernel.org
Link: https://sourceware.org/bugzilla/show_bug.cgi?id=24554
Link: https://github.com/ClangBuiltLinux/linux/issues/448
Reported-by: Nathan Chancellor <natechancellor@gmail.com>
Suggested-by: Alan Modra <amodra@gmail.com>
Suggested-by: Jordan Rupprect <rupprecht@google.com>
Suggested-by: Kees Cook <keescook@chromium.org>
Acked-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
This backport is for 4.14.  It should allow us to use llvm-objcopy for
RELR relocations on arm64 in Android.

 drivers/misc/Makefile | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
index ad0e64fdba34..76f6a4f628b3 100644
--- a/drivers/misc/Makefile
+++ b/drivers/misc/Makefile
@@ -69,8 +69,7 @@ KCOV_INSTRUMENT_lkdtm_rodata.o	:= n
 
 OBJCOPYFLAGS :=
 OBJCOPYFLAGS_lkdtm_rodata_objcopy.o := \
-			--set-section-flags .text=alloc,readonly \
-			--rename-section .text=.rodata
+	--rename-section .text=.rodata,alloc,readonly,load
 targets += lkdtm_rodata.o lkdtm_rodata_objcopy.o
 $(obj)/lkdtm_rodata_objcopy.o: $(obj)/lkdtm_rodata.o FORCE
 	$(call if_changed,objcopy)
-- 
2.23.0.rc1.153.gdeed80330f-goog

Re: [4.14 PATCH] lkdtm: support llvm-objcopy

[Greg Kroah-Hartman]

On Mon, Aug 12, 2019 at 02:17:50PM -0700, Nick Desaulniers wrote:
> This backport is for 4.14.  It should allow us to use llvm-objcopy for
> RELR relocations on arm64 in Android.

I don't object to this, but the odds that you are actually using the
lkdtm driver on Android systems is pretty slim :)

thanks,

greg k-h