From: "H. Peter Anvin" <hpa@zytor.com>
To: Kees Cook <keescook@chromium.org>, Peter Zijlstra <peterz@infradead.org>
Cc: Kristen Carlson Accardi <kristen@linux.intel.com>,
Thomas Garnier <thgarnie@chromium.org>,
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 10:44:52 -0800 [thread overview]
Message-ID: <e60876d0-4f7d-9523-bcec-6d002f717623@zytor.com> (raw)
In-Reply-To: <202003041019.C6386B2F7@keescook>
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?
>
> 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.
The huge memory model, required for arbitrary placement, has a very
significant performance impact.
The assembly code is *very* different across memory models.
-hpa
next prev parent reply other threads:[~2020-03-04 18:46 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 [this message]
2020-03-04 19:19 ` Thomas Garnier
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=e60876d0-4f7d-9523-bcec-6d002f717623@zytor.com \
--to=hpa@zytor.com \
--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=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=thgarnie@chromium.org \
--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).