Re: noexecstack

[orc <orc@sibserver.ru>]

On Mon, 6 Aug 2012 10:46:56 +0200
Daniel Cegiełka <daniel.cegielka@gmail.com> wrote:

> 2012/8/6 orc <orc@sibserver.ru>:
> > On Mon, 6 Aug 2012 09:16:10 +0200
> > Daniel Cegiełka <daniel.cegielka@gmail.com> wrote:
> >
> 
> >> It would be very nice if we could solve this problem in this way.
> >> I'm currently using this patch, but this is not the best solution
> >> in my opinion. Ideally if the system (kernel, binutils, libc)
> >> enforce noexecstack by default... definitely worth look closer at
> >> this issue.
> >
> > Consider this patch as enforcing binutils' noexecstack by default:
> >
> > diff -Naur binutils-2.17.50.0.17.o/ld/ldmain.c
> > binutils-2.17.50.0.17/ld/ldmain.c ---
> > binutils-2.17.50.0.17.o/ld/ldmain.c     2007-06-19
> > 01:31:40.000000000 +0800 +++ binutils-2.17.50.0.17/ld/ldmain.c
> > 2012-08-03 19:59:26.658980680 +0800 @@ -281,6 +281,8 @@
> > link_info.pei386_auto_import = -1; link_info.spare_dynamic_tags = 5;
> >    link_info.sharable_sections = FALSE;
> > +  link_info.execstack = FALSE;
> > +  link_info.noexecstack = TRUE;
> >
> >    ldfile_add_arch ("");
> >    emulation = get_emulation (argc, argv);
> >
> > (this one for binutils 2.17.50.0.17, recent maybe patched with
> > finding where link_info is initialized and appending this two lines)
> >
> > GCC generates same .note.GNU-stack section definition in it's asm
> > output, as seen in your patch, but I don't know when it needs
> > executable stack and generates another definition.
> 
> I'm afraid that this option will not work with .S files. Here is a
> comment to this feature:
> 
> http://www.cygwin.com/ml/binutils/2003-06/msg00128.html
> 
> Here is another patch:
> 
> http://sourceware.org/ml/binutils/2003-05/msg00741.html
> 
> it's like in the Vasily's patch with stack flags (PF_R | PF_W | PF_X):
> 
> http://www.openwall.com/lists/owl-dev/2012/08/05/3
> 
> Daniel

It seems that this is under GCC control (NEED_INDICATE_EXEC_STACK
macro, related subroutine in gcc/varasm.c). If .S has no .note.GNU-stack
section definition, than the produced .o file will be clean from it and
it will be task of binutils' ld to decide create executable stack
segment or not.
If you about .S files that are parts of musl, then this patch will be
enough. It is the same of -z noexecstack.

(Ideal situation here is that all the code can work with non-executable
stack and there are no such ugly extensions in ELF)