[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <e60876d0-4f7d-9523-bcec-6d002f717623@zytor.com>
Date: Wed, 4 Mar 2020 10:44:52 -0800
From: "H. Peter Anvin" <hpa@...or.com>
To: Kees Cook <keescook@...omium.org>, Peter Zijlstra <peterz@...radead.org>
Cc: Kristen Carlson Accardi <kristen@...ux.intel.com>,
Thomas Garnier <thgarnie@...omium.org>,
Thomas Gleixner
<tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
Borislav Petkov <bp@...en8.de>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Herbert Xu <herbert@...dor.apana.org.au>,
"David S. Miller" <davem@...emloft.net>,
the arch/x86 maintainers <x86@...nel.org>,
Andy Lutomirski
<luto@...nel.org>, Juergen Gross <jgross@...e.com>,
Thomas Hellstrom <thellstrom@...are.com>,
"VMware, Inc." <pv-drivers@...are.com>,
"Rafael J. Wysocki"
<rjw@...ysocki.net>,
Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
Rasmus Villemoes <linux@...musvillemoes.dk>,
Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
Will Deacon
<will@...nel.org>, Ard Biesheuvel <ardb@...nel.org>,
Masami Hiramatsu <mhiramat@...nel.org>, Jiri Slaby <jslaby@...e.cz>,
Boris Ostrovsky <boris.ostrovsky@...cle.com>,
Josh Poimboeuf <jpoimboe@...hat.com>,
Cao jin <caoj.fnst@...fujitsu.com>,
Allison Randal <allison@...utok.net>,
Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
virtualization@...ts.linux-foundation.org,
Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: [PATCH v11 00/11] x86: PIE support to extend KASLR randomization
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
Powered by blists - more mailing lists
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
