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SubjectRe: [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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