linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Thomas Garnier <thgarnie@chromium.org>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Kristen Carlson Accardi <kristen@linux.intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	Kernel Hardening <kernel-hardening@lists.openwall.com>,
	Herbert Xu <herbert@gondor.apana.org.au>,
	"David S. Miller" <davem@davemloft.net>,
	"the arch/x86 maintainers" <x86@kernel.org>,
	Andy Lutomirski <luto@kernel.org>,
	Juergen Gross <jgross@suse.com>,
	Thomas Hellstrom <thellstrom@vmware.com>,
	"VMware, Inc." <pv-drivers@vmware.com>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Len Brown <len.brown@intel.com>, Pavel Machek <pavel@ucw.cz>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
	Will Deacon <will@kernel.org>, Ard Biesheuvel <ardb@kernel.org>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Jiri Slaby <jslaby@suse.cz>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Cao jin <caoj.fnst@cn.fujitsu.com>,
	Allison Randal <allison@lohutok.net>,
	Linux Crypto Mailing List <linux-crypto@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	virtualization@lists.linux-foundation.org,
	Linux PM list <linux-pm@vger.kernel.org>
Subject: Re: [PATCH v11 00/11] x86: PIE support to extend KASLR randomization
Date: Wed, 4 Mar 2020 11:19:44 -0800	[thread overview]
Message-ID: <CAJcbSZHBB1u2Vq0jZKsmd0UcRj=aichxTtbGvbWgf8-g8WPa7w@mail.gmail.com> (raw)
In-Reply-To: <e60876d0-4f7d-9523-bcec-6d002f717623@zytor.com>

On Wed, Mar 4, 2020 at 10:45 AM H. Peter Anvin <hpa@zytor.com> wrote:
>
> On 2020-03-04 10:21, Kees Cook wrote:
> > On Wed, Mar 04, 2020 at 10:21:36AM +0100, Peter Zijlstra wrote:
> >> But at what cost; it does unspeakable ugly to the asm. And didn't a
> >> kernel compiled with the extended PIE range produce a measurably slower
> >> kernel due to all the ugly?
> >
> > Was that true? I thought the final results were a wash and that earlier
> > benchmarks weren't accurate for some reason? I can't find the thread
> > now. Thomas, do you have numbers on that?

I have never seen a significant performance impact. Performance and
size is better on more recent versions of gcc as it has better
generation of PIE code (for example generation of switches).

> >
> > BTW, I totally agree that fgkaslr is the way to go in the future. I
> > am mostly arguing for this under the assumption that it doesn't
> > have meaningful performance impact and that it gains the kernel some
> > flexibility in the kinds of things it can do in the future. If the former
> > is not true, then I'd agree, the benefit needs to be more clear.
> >
>
> "Making the assembly really ugly" by itself is a reason not to do it, in my
> Not So Humble Opinion[TM]; but the reason the kernel and small memory models
> exist in the first place is because there is a nonzero performance impact of
> the small-PIC memory model. Having modules in separate regions would further
> add the cost of a GOT references all over the place (PLT is optional, useless
> and deprecated for eager binding) *plus* might introduce at least one new
> vector of attack: overwrite a random GOT slot, and just wait until it gets hit
> by whatever code path it happens to be in; the exact code path doesn't matter.
> From an kASLR perspective this is *very* bad, since you only need to guess the
> general region of a GOT rather than an exact address.

I agree that it would add GOT references and I can explore that more
in terms of performance impact and size. This patchset makes the GOT
readonly too so I don't think the attack vector applies.

>
> The huge memory model, required for arbitrary placement, has a very
> significant performance impact.

I assume you mean mcmodel=large, it doesn't use it. It uses -fPIE and
removes -mcmodel=kernel. It favors relative references whenever
possible.

>
> The assembly code is *very* different across memory models.
>
>         -hpa

  reply	other threads:[~2020-03-04 19:20 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-28  0:00 [PATCH v11 00/11] x86: PIE support to extend KASLR randomization Thomas Garnier
2020-02-28  0:00 ` [PATCH v11 01/11] x86/crypto: Adapt assembly for PIE support Thomas Garnier
2020-02-28  0:00 ` [PATCH v11 02/11] x86: Add macro to get symbol address " Thomas Garnier
2020-02-28  0:00 ` [PATCH v11 03/11] x86: relocate_kernel - Adapt assembly " Thomas Garnier
2020-02-28  0:00 ` [PATCH v11 04/11] x86/entry/64: " Thomas Garnier
2020-02-28  0:00 ` [PATCH v11 05/11] x86: pm-trace - " Thomas Garnier
2020-02-28  0:00 ` [PATCH v11 06/11] x86/CPU: " Thomas Garnier
2020-03-03  4:58   ` Kees Cook
2020-02-28  0:00 ` [PATCH v11 07/11] x86/acpi: " Thomas Garnier
2020-02-28  0:00 ` [PATCH v11 08/11] x86/boot/64: " Thomas Garnier
2020-02-28  0:00 ` [PATCH v11 09/11] x86/power/64: " Thomas Garnier
2020-02-28  0:00 ` [PATCH v11 10/11] x86/paravirt: " Thomas Garnier
2020-02-28  0:00 ` [PATCH v11 11/11] x86/alternatives: " Thomas Garnier
2020-03-03  4:59   ` Kees Cook
2020-03-03  5:02 ` [PATCH v11 00/11] x86: PIE support to extend KASLR randomization Kees Cook
2020-03-03  9:55   ` Peter Zijlstra
2020-03-03 15:43     ` Thomas Garnier
2020-03-03 21:01       ` Kristen Carlson Accardi
2020-03-03 21:19         ` Kees Cook
2020-03-04  9:21           ` Peter Zijlstra
2020-03-04 18:21             ` Kees Cook
2020-03-04 18:44               ` H. Peter Anvin
2020-03-04 19:19                 ` Thomas Garnier [this message]
2020-03-04 19:22                   ` H. Peter Anvin
2020-03-04  9:40           ` H. Peter Anvin

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to='CAJcbSZHBB1u2Vq0jZKsmd0UcRj=aichxTtbGvbWgf8-g8WPa7w@mail.gmail.com' \
    --to=thgarnie@chromium.org \
    --cc=allison@lohutok.net \
    --cc=ardb@kernel.org \
    --cc=boris.ostrovsky@oracle.com \
    --cc=bp@alien8.de \
    --cc=caoj.fnst@cn.fujitsu.com \
    --cc=davem@davemloft.net \
    --cc=herbert@gondor.apana.org.au \
    --cc=hpa@zytor.com \
    --cc=jgross@suse.com \
    --cc=jpoimboe@redhat.com \
    --cc=jslaby@suse.cz \
    --cc=keescook@chromium.org \
    --cc=kernel-hardening@lists.openwall.com \
    --cc=kristen@linux.intel.com \
    --cc=len.brown@intel.com \
    --cc=linux-crypto@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-pm@vger.kernel.org \
    --cc=linux@rasmusvillemoes.dk \
    --cc=luto@kernel.org \
    --cc=mhiramat@kernel.org \
    --cc=miguel.ojeda.sandonis@gmail.com \
    --cc=mingo@redhat.com \
    --cc=pavel@ucw.cz \
    --cc=peterz@infradead.org \
    --cc=pv-drivers@vmware.com \
    --cc=rjw@rjwysocki.net \
    --cc=tglx@linutronix.de \
    --cc=thellstrom@vmware.com \
    --cc=virtualization@lists.linux-foundation.org \
    --cc=will@kernel.org \
    --cc=x86@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).