Re: [PATCH v3] lkdtm: support llvm-objcopy

[Nathan Chancellor <natechancellor@gmail.com>]

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On Thu, May 16, 2019 at 09:06:13PM -0700, Nathan Chancellor wrote:
> On Fri, May 17, 2019 at 12:10:02AM +0000, Sasha Levin wrote:
> > Hi,
> > 
> > [This is an automated email]
> > 
> > This commit has been processed because it contains a -stable tag.
> > The stable tag indicates that it's relevant for the following trees: all
> 
> Nick, the stable tag should probably specify 4.8+ since the commit it
> fixes came in during 4.8-rc1.
> 
> Cc: stable@vger.kernel.org # 4.8+
> 
> Might also help to add:
> 
> Fixes: 9a49a528dcf3 ("lkdtm: add function for testing .rodata section")
> 
> > 
> > The bot has tested the following trees: v5.1.2, v5.0.16, v4.19.43, v4.14.119, v4.9.176, v4.4.179, v3.18.140.
> > 
> > v5.1.2: Build OK!
> > v5.0.16: Build OK!
> > v4.19.43: Build OK!
> > v4.14.119: Failed to apply! Possible dependencies:
> >     039a1c42058d ("lkdtm: Relocate code to subdirectory")
> 
> However, it will still need a manual backport because of the lack of
> this commit. I've attached the current patch backported for reference,

Would help if I actually did this... :^)

> the git am flags '-3 -p4 --directory=drivers/misc' help get it proper
> then the conflict is rather easy to resolve.
> 
> Thanks,
> Nathan

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From 10c0a74a8d92669b91b66efe6b72550fc24e8e7d Mon Sep 17 00:00:00 2001
From: Nick Desaulniers <ndesaulniers@google.com>
Date: Wed, 15 May 2019 11:24:41 -0700
Subject: [PATCH] lkdtm: support llvm-objcopy

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: Nathan Chancellor <natechancellor@gmail.com>
---
 drivers/misc/Makefile | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
index c3c8624f4d95..805835c2b99b 100644
--- a/drivers/misc/Makefile
+++ b/drivers/misc/Makefile
@@ -70,8 +70,7 @@ 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)
-- 
2.22.0.rc0