Re: [PATCH v2] lkdtm: support llvm-objcopy
From: Nathan Chancellor
Date: Wed May 15 2019 - 14:21:06 EST
On Wed, May 15, 2019 at 11:12:04AM -0700, 'Nick Desaulniers' via Clang Built Linux wrote:
> With CONFIG_LKDTM=y and make OBJCOPY=llvm-objcopy, llvm-objcopy errors:
> llvm-objcopy: error: --set-section-flags=.text conflicts with
> 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@xxxxxxxxxxxxxxx
> Link: https://sourceware.org/bugzilla/show_bug.cgi?id=24554
> Link: https://github.com/ClangBuiltLinux/linux/issues/448
> Reported-by: Nathan Chancellor <nathanchance@xxxxxxxxx>
Doesn't look like this got updated. I don't want to make you send a v3
just for that though since it's purely cosmetic and adding my tag below
will ensure I get copied on any backports and such.
> Suggested-by: Alan Modra <amodra@xxxxxxxxx>
> Suggested-by: Jordan Rupprect <rupprecht@xxxxxxxxxx>
> Suggested-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Reviewed-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
> 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)