From: Paul Turner <pjt@google.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: "Woodhouse, David" <dwmw@amazon.co.uk>,
"Van De Ven, Arjan" <arjan.van.de.ven@intel.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"tim.c.chen@linux.intel.com" <tim.c.chen@linux.intel.com>,
"peterz@infradead.org" <peterz@infradead.org>,
"torvalds@linux-foundation.org" <torvalds@linux-foundation.org>,
"tglx@linuxtronix.de" <tglx@linuxtronix.de>,
"riel@redhat.com" <riel@redhat.com>,
"keescook@google.com" <keescook@google.com>,
"gnomes@lxorguk.ukuu.org.uk" <gnomes@lxorguk.ukuu.org.uk>,
"dave.hansen@intel.com" <dave.hansen@intel.com>,
"jikos@kernel.org" <jikos@kernel.org>,
"gregkh@linux-foundation.org" <gregkh@linux-foundation.org>
Subject: Re: [RFC] Retpoline: Binary mitigation for branch-target-injection (aka "Spectre")
Date: Fri, 5 Jan 2018 02:49:44 -0800 [thread overview]
Message-ID: <20180105104944.GB253582@google.com> (raw)
In-Reply-To: <CALCETrWRca6X9AbXn2b_p_mbY9gAws3LFwsDxWw5Vk9zDLAwbg@mail.gmail.com>
On Thu, Jan 04, 2018 at 08:18:57AM -0800, Andy Lutomirski wrote:
> On Thu, Jan 4, 2018 at 1:30 AM, Woodhouse, David <dwmw@amazon.co.uk> wrote:
> > On Thu, 2018-01-04 at 01:10 -0800, Paul Turner wrote:
> >> Apologies for the discombobulation around today's disclosure. Obviously the
> >> original goal was to communicate this a little more coherently, but the
> >> unscheduled advances in the disclosure disrupted the efforts to pull this
> >> together more cleanly.
> >>
> >> I wanted to open discussion the "retpoline" approach and and define its
> >> requirements so that we can separate the core
> >> details from questions regarding any particular implementation thereof.
> >>
> >> As a starting point, a full write-up describing the approach is available at:
> >> https://support.google.com/faqs/answer/7625886
> >
> > Note that (ab)using 'ret' in this way is incompatible with CET on
> > upcoming processors. HJ added a -mno-indirect-branch-register option to
> > the latest round of GCC patches, which puts the branch target in a
> > register instead of on the stack. My kernel patches (which I'm about to
> > reconcile with Andi's tweaks and post) do the same.
> >
> > That means that in the cases where at runtime we want to ALTERNATIVE
> > out the retpoline, it just turns back into a bare 'jmp *\reg'.
> >
> >
>
> I hate to say this, but I think Intel should postpone CET until the
> dust settles. Intel should also consider a hardware-protected stack
> that is only accessible with PUSH, POP, CALL, RET, and a new MOVSTACK
> instruction. That, by itself, would give considerable protection.
> But we still need JMP_NO_SPECULATE. Or, better yet, get the CPU to
> stop leaking data during speculative execution.
Echoing Andy's thoughts, but from a slightly different angle:
1) BTI is worse than the current classes of return attack. Given this,
considered as a binary choice, it's equivalent to the current state of the
world (e.g. no CET).
2) CET will not be "free". I suspect in its initial revisions it will be more
valuable for protecting end-users then enterprise workloads (cost is not
observable for interactive workloads because there's tons of headroom in the
first place).
While the potential incompatibility is unfortunate; I'm not sure it makes a
significant adoption to the adoption rate of CET.
next prev parent reply other threads:[~2018-01-05 10:49 UTC|newest]
Thread overview: 79+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-04 9:10 [RFC] Retpoline: Binary mitigation for branch-target-injection (aka "Spectre") Paul Turner
2018-01-04 9:12 ` Paul Turner
2018-01-04 9:24 ` Paul Turner
2018-01-04 9:48 ` Greg Kroah-Hartman
2018-01-04 9:56 ` Woodhouse, David
2018-01-04 9:30 ` Woodhouse, David
2018-01-04 14:36 ` [PATCH v3 01/13] x86/retpoline: Add initial retpoline support David Woodhouse
2018-01-04 18:03 ` Linus Torvalds
2018-01-04 19:32 ` Woodhouse, David
2018-01-04 18:17 ` Alexei Starovoitov
2018-01-04 18:25 ` Linus Torvalds
2018-01-04 18:36 ` Alexei Starovoitov
2018-01-04 19:27 ` David Woodhouse
2018-01-05 10:28 ` Paul Turner
2018-01-05 10:55 ` David Woodhouse
2018-01-05 11:19 ` Paul Turner
2018-01-05 11:25 ` Paul Turner
2018-01-05 11:26 ` Paolo Bonzini
2018-01-05 12:20 ` Paul Turner
2018-01-05 10:40 ` Paul Turner
2018-01-04 18:40 ` Andi Kleen
2018-01-05 10:32 ` Paul Turner
2018-01-05 12:54 ` Thomas Gleixner
2018-01-05 13:01 ` Juergen Gross
2018-01-05 13:03 ` Thomas Gleixner
2018-01-05 13:56 ` Woodhouse, David
2018-01-05 16:41 ` Woodhouse, David
2018-01-05 16:45 ` Borislav Petkov
2018-01-05 17:08 ` Josh Poimboeuf
2018-01-06 0:30 ` Borislav Petkov
2018-01-06 8:23 ` David Woodhouse
2018-01-06 17:02 ` Borislav Petkov
2018-01-07 9:40 ` David Woodhouse
2018-01-07 11:46 ` Borislav Petkov
2018-01-07 12:21 ` David Woodhouse
2018-01-07 14:03 ` Borislav Petkov
2018-01-08 21:50 ` David Woodhouse
2018-01-08 5:06 ` Josh Poimboeuf
2018-01-08 7:55 ` Woodhouse, David
2018-01-05 17:12 ` Woodhouse, David
2018-01-05 17:28 ` Linus Torvalds
2018-01-05 17:48 ` David Woodhouse
2018-01-05 18:05 ` Andi Kleen
2018-01-05 20:32 ` Woodhouse, David
2018-01-05 21:11 ` Brian Gerst
2018-01-05 22:16 ` Woodhouse, David
2018-01-05 22:43 ` Borislav Petkov
2018-01-05 22:00 ` Woodhouse, David
2018-01-05 22:06 ` Borislav Petkov
2018-01-05 23:50 ` Linus Torvalds
2018-01-06 10:53 ` Woodhouse, David
2018-01-04 14:36 ` [PATCH v3 02/13] x86/retpoline/crypto: Convert crypto assembler indirect jumps David Woodhouse
2018-01-04 14:37 ` [PATCH v3 03/13] x86/retpoline/entry: Convert entry " David Woodhouse
2018-01-04 14:46 ` Dave Hansen
2018-01-04 14:49 ` Woodhouse, David
2018-01-04 14:37 ` [PATCH v3 04/13] x86/retpoline/ftrace: Convert ftrace " David Woodhouse
2018-01-04 14:37 ` [PATCH v3 05/13] x86/retpoline/hyperv: Convert " David Woodhouse
2018-01-04 14:37 ` [PATCH v3 06/13] x86/retpoline/xen: Convert Xen hypercall " David Woodhouse
2018-01-04 15:10 ` Juergen Gross
2018-01-04 15:18 ` David Woodhouse
2018-01-04 15:54 ` Juergen Gross
2018-01-04 14:37 ` [PATCH v3 07/13] x86/retpoline/checksum32: Convert assembler " David Woodhouse
2018-01-04 14:37 ` [PATCH v3 08/13] x86/alternatives: Add missing \n at end of ALTERNATIVE inline asm David Woodhouse
2018-01-05 13:04 ` [tip:x86/pti] x86/alternatives: Add missing '\n' " tip-bot for David Woodhouse
2018-01-04 14:37 ` [PATCH v3 09/13] x86/retpoline/irq32: Convert assembler indirect jumps David Woodhouse
2018-01-04 14:37 ` [PATCH v3 10/13] x86/retpoline/pvops: " David Woodhouse
2018-01-04 15:02 ` Juergen Gross
2018-01-04 15:12 ` Woodhouse, David
2018-01-04 15:18 ` Andrew Cooper
2018-01-04 16:04 ` Juergen Gross
2018-01-04 16:37 ` Andi Kleen
2018-01-04 14:37 ` [PATCH v3 11/13] retpoline/taint: Taint kernel for missing retpoline in compiler David Woodhouse
2018-01-04 22:06 ` Justin Forbes
2018-01-04 14:37 ` [PATCH v3 12/13] retpoline/objtool: Disable some objtool warnings David Woodhouse
2018-01-04 14:37 ` [PATCH v3 13/13] retpoline: Attempt to quiten objtool warning for unreachable code David Woodhouse
2018-01-04 16:18 ` [RFC] Retpoline: Binary mitigation for branch-target-injection (aka "Spectre") Andy Lutomirski
2018-01-04 16:24 ` David Woodhouse
2018-01-05 10:49 ` Paul Turner [this message]
2018-01-05 11:43 ` Woodhouse, David
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