linux-kernel - [PATCH v2] lkdtm: support llvm-objcopy

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Date:   Wed, 15 May 2019 11:12:04 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     gregkh@...uxfoundation.org
Cc:     clang-built-linux@...glegroups.com,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        stable@...r.kernel.org, Nathan Chancellor <nathanchance@...il.com>,
        Alan Modra <amodra@...il.com>,
        Jordan Rupprect <rupprecht@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org
Subject: [PATCH v2] 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@...r.kernel.org
Link: https://sourceware.org/bugzilla/show_bug.cgi?id=24554
Link: https://github.com/ClangBuiltLinux/linux/issues/448
Reported-by: Nathan Chancellor <nathanchance@...il.com>
Suggested-by: Alan Modra <amodra@...il.com>
Suggested-by: Jordan Rupprect <rupprecht@...gle.com>
Suggested-by: Kees Cook <keescook@...omium.org>
Acked-by: Kees Cook <keescook@...omium.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
---
Changes from v1 -> v2:
* add load flag, as per Kees and Alan.
* update commit message to mention reason for load flag.
* add Kees' and Alan's suggested by.
* carry Kees' Ack.
* cc stable.

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

diff --git a/drivers/misc/lkdtm/Makefile b/drivers/misc/lkdtm/Makefile
index 951c984de61a..fb10eafe9bde 100644
--- a/drivers/misc/lkdtm/Makefile
+++ b/drivers/misc/lkdtm/Makefile
@@ -15,8 +15,7 @@ KCOV_INSTRUMENT_rodata.o	:= n
 
 OBJCOPYFLAGS :=
 OBJCOPYFLAGS_rodata_objcopy.o	:= \
-			--set-section-flags .text=alloc,readonly \
-			--rename-section .text=.rodata
+			--rename-section .text=.rodata,alloc,readonly,load
 targets += rodata.o rodata_objcopy.o
 $(obj)/rodata_objcopy.o: $(obj)/rodata.o FORCE
 	$(call if_changed,objcopy)
-- 
2.21.0.1020.gf2820cf01a-goog