From: Kees Cook <keescook@chromium.org>
To: Hector Marco-Gisbert <hecmargi@upv.es>
Cc: LKML <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
"x86@kernel.org" <x86@kernel.org>,
Ismael Ripoll Ripoll <iripoll@upv.es>,
Harvey Harrison <harvey.harrison@gmail.com>,
Arjan van de Ven <arjan@linux.intel.com>
Subject: Re: [PATCH] x86: Enable full randomization on i386 and X86_32.
Date: Thu, 10 Mar 2016 12:23:36 -0800 [thread overview]
Message-ID: <CAGXu5jJRVrMxgO0G2BjU2Ks=Pa1RcG3LidqXPe9zb-V1LbQv4g@mail.gmail.com> (raw)
In-Reply-To: <1457639460-5242-1-git-send-email-hecmargi@upv.es>
On Thu, Mar 10, 2016 at 11:51 AM, Hector Marco-Gisbert <hecmargi@upv.es> wrote:
> Currently on i386 and on X86_64 when emulating X86_32 in legacy mode, only
> the stack and the executable are randomized but not other mmapped files
> (libraries, vDSO, etc.). This patch enables randomization for the
> libraries, vDSO and mmap requests on i386 and in X86_32 in legacy mode.
>
> By default on i386 there are 8 bits for the randomization of the libraries,
> vDSO and mmaps which only uses 1MB of VA.
>
> This patch preserves the original randomness, using 1MB of VA out of 3GB or
> 4GB. We think that 1MB out of 3GB is not a big cost for having the ASLR.
>
> The first obvious security benefit is that all objects are randomized (not
> only the stack and the executable) in legacy mode which highly increases
> the ASLR effectiveness, otherwise the attackers may use these
> non-randomized areas. But also sensitive setuid/setgid applications are
> more secure because currently, attackers can disable the randomization of
> these applications by setting the ulimit stack to "unlimited". This is a
> very old and widely known trick to disable the ASLR in i386 which has been
> allowed for too long.
>
> Another trick used to disable the ASLR was to set the ADDR_NO_RANDOMIZE
> personality flag, but fortunately this doesn't work on setuid/setgid
> applications because there is security checks which clear Security-relevant
> flags.
>
> This patch always randomizes the mmap_legacy_base address, removing the
> possibility to disable the ASLR by setting the stack to "unlimited".
>
>
> Signed-off-by: Hector Marco-Gisbert <hecmargi@upv.es>
> Signed-off-by: Ismael Ripoll Ripoll <iripoll@upv.es>
Thanks! This has bugged me for a long time. :)
Acked-by: Kees Cook <keescook@chromium.org>
Arjan, or other folks, can you remember why x86_32 disabled mmap
randomization here? There doesn't seem to be a good reason for it that
I see.
-Kees
> ---
> arch/x86/mm/mmap.c | 14 +-------------
> 1 file changed, 1 insertion(+), 13 deletions(-)
>
> diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
> index 72bb52f..d2dc043 100644
> --- a/arch/x86/mm/mmap.c
> +++ b/arch/x86/mm/mmap.c
> @@ -94,18 +94,6 @@ static unsigned long mmap_base(unsigned long rnd)
> }
>
> /*
> - * Bottom-up (legacy) layout on X86_32 did not support randomization, X86_64
> - * does, but not when emulating X86_32
> - */
> -static unsigned long mmap_legacy_base(unsigned long rnd)
> -{
> - if (mmap_is_ia32())
> - return TASK_UNMAPPED_BASE;
> - else
> - return TASK_UNMAPPED_BASE + rnd;
> -}
> -
> -/*
> * This function, called very early during the creation of a new
> * process VM image, sets up which VM layout function to use:
> */
> @@ -116,7 +104,7 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
> if (current->flags & PF_RANDOMIZE)
> random_factor = arch_mmap_rnd();
>
> - mm->mmap_legacy_base = mmap_legacy_base(random_factor);
> + mm->mmap_legacy_base = TASK_UNMAPPED_BASE + random_factor;
>
> if (mmap_is_legacy()) {
> mm->mmap_base = mm->mmap_legacy_base;
> --
> 1.9.1
>
--
Kees Cook
Chrome OS & Brillo Security
next prev parent reply other threads:[~2016-03-10 20:23 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-10 19:51 [PATCH] x86: Enable full randomization on i386 and X86_32 Hector Marco-Gisbert
2016-03-10 20:23 ` Kees Cook [this message]
2016-03-10 20:53 ` Arjan van de Ven
2016-03-10 21:05 ` Kees Cook
2016-03-11 8:53 ` Ingo Molnar
2016-03-11 16:19 ` Kees Cook
2016-03-11 8:51 ` Ingo Molnar
2016-03-12 15:15 ` [tip:x86/mm] x86/mm/32: " tip-bot for Hector Marco-Gisbert
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