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Date: Fri, 2 Jun 2017 12:27:44 -0700
From: Kees Cook <keescook@...omium.org>
To: Rik van Riel <riel@...hat.com>
Cc: LKML <linux-kernel@...r.kernel.org>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
Andrew Morton <akpm@...ux-foundation.org>, Ingo Molnar <mingo@...nel.org>,
Oleg Nesterov <oleg@...hat.com>, Larry Woodman <lwoodman@...hat.com>, mhocko@...e.de,
Daniel Micay <danielmicay@...il.com>, Will Deacon <will.deacon@....com>,
"benh@...nel.crashing.org" <benh@...nel.crashing.org>
Subject: Re: [PATCH 1/6] binfmt_elf: document load_bias a
little bit
On Fri, Jun 2, 2017 at 8:20 AM, <riel@...hat.com> wrote:
> From: Rik van Riel <riel@...hat.com>
>
> After me and another unnamed developer got confused by the subtraction
> of vaddr in this branch of the code, followed by adding vaddr back in
> a little bit later, for the third time, maybe it is time to document
> this quirky bit of code.
>
> Signed-off-by: Rik van Riel <riel@...hat.com>
Acked-by: Kees Cook <keescook@...omium.org>
Any and all improvements to this code and its documentation are welcome. :)
-Kees
> ---
> fs/binfmt_elf.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> index 5075fd5c62c8..8c3f4dbc7603 100644
> --- a/fs/binfmt_elf.c
> +++ b/fs/binfmt_elf.c
> @@ -930,10 +930,16 @@ static int load_elf_binary(struct linux_binprm *bprm)
> if (loc->elf_ex.e_type == ET_EXEC || load_addr_set) {
> elf_flags |= MAP_FIXED;
> } else if (loc->elf_ex.e_type == ET_DYN) {
> - /* Try and get dynamic programs out of the way of the
> + /*
> + * Try and get dynamic programs out of the way of the
> * 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. */
> + * follow the loader, and is not movable.
> + *
> + * The load_bias is the difference between the address
> + * in the elf header and the address where the binary
> + * is mmapped.
> + */
> load_bias = ELF_ET_DYN_BASE - vaddr;
> if (current->flags & PF_RANDOMIZE)
> load_bias += arch_mmap_rnd();
> --
> 2.9.3
>
--
Kees Cook
Pixel Security
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