linux-kernel - Re: [PATCH] [RESEND] PIE executable randomization

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Date:	Tue, 14 Aug 2007 16:06:47 -0400
From:	Jakub Jelinek <jakub@...hat.com>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Roland McGrath <roland@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Ulrich Kunitz <kune@...ne-taler.de>,
	Bret Towe <magnade@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [RESEND] PIE executable randomization

On Wed, Aug 08, 2007 at 04:03:07PM +0200, Jiri Kosina wrote:
> @@ -870,11 +917,15 @@ static int load_elf_binary(struct linux_binprm *bprm, struct pt_regs *regs)
>  			 * default mmap base, as well as whatever program they
>  			 * might try to exec.  This is because the brk will
>  			 * follow the loader, and is not movable.  */
> +#ifdef CONFIG_X86
> +			load_bias = 0;
> +#else
>  			load_bias = ELF_PAGESTART(ELF_ET_DYN_BASE - vaddr);
> +#endif
>  		}
>  
>  		error = elf_map(bprm->file, load_bias + vaddr, elf_ppnt,
> -				elf_prot, elf_flags);
> +				elf_prot, elf_flags,0);
>  		if (BAD_ADDR(error)) {
>  			send_sig(SIGKILL, current, 0);
>  			retval = IS_ERR((void *)error) ?

If I'm reading the above hunk correctly, this means we will randomize
all PIEs and even all dynamic linkers invoked as executables on i?86 and
x86_64, and on the rest of arches we won't randomize at all, instead
load ET_DYN objects at ELF_ET_DYN_BASE address.

But I don't see anything i?86/x86_64 specific on this.

What would make much more sense to me would be conditionalizing on
whether we are loading a dynamic linker (in which case loading it
at ELF_ET_DYN_BASE is desirable or not (PIEs, ...; and for PIEs we
want to randomize on all architectures).

So something like
			if (elf_interpreter)
				load_bias = 0;
			else
				/* Probably dynamic linker invoked as
				   /lib*/ld*so* program args - load at
				   ELF_ET_DYN_BASE.  */
				load_bias = ELF_PAGESTART(ELF_ET_DYN_BASE - vaddr);
instead of
#ifdef CONFIG_X86
			load_bias = 0;
#else
			load_bias = ELF_PAGESTART(ELF_ET_DYN_BASE - vaddr);
#endif

	Jakub
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