Re: [PATCH] binfmt_elf: randomize PIE binaries

On Thu, Oct 19, 2006 at 04:23:54PM -0400, Dave Jones wrote:
On Thu, Oct 19, 2006 at 04:35:47PM +0200, Marcus Meissner wrote:

> --- linux-2.6.18/fs/binfmt_elf.c.xx 2006-10-19 11:21:49.000000000 +0200
> +++ linux-2.6.18/fs/binfmt_elf.c 2006-10-19 11:24:58.000000000 +0200
> @@ -856,7 +856,12 @@ static int load_elf_binary(struct linux_
> * 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. */
> - load_bias = ELF_PAGESTART(ELF_ET_DYN_BASE - vaddr);
> + if (current->flags & PF_RANDOMIZE)
> + load_bias = randomize_range(0, ELF_ET_DYN_BASE,
> + vaddr);
> + else
> + load_bias = ELF_ET_DYN_BASE - vaddr;
> + load_bias = ELF_PAGESTART(load_bias);
> }
>
> error = elf_map(bprm->file, load_bias + vaddr, elf_ppnt,


vaddr seems odd to be using as the len for randomize_range doesn't it ?
Should that be randomize_range(0, ELF_ET_DYN_BASE, ELF_ET_DYN_BASE - vaddr);

maybe ?

Also, when we get to the elf_map(), we add vaddr back again, but in the
randomize_range case, we never subtracted it. hmm?

Yes, the code was not really doing what I actually intended. (It was working,
but the range always started at vaddr).

I am using randomize_range (PAGE_SIZE, ELF_ET_DYN_BASE,0) (- vaddr) now
after further comments from Arjan.

Any other good ideas for a range to do the randomization in are welcome.

Ciao, Marcus
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