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From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: David Woodhouse <dwmw@amazon.co.uk>,
	Andi Kleen <ak@linux.intel.com>, Paul Turner <pjt@google.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Greg Kroah-Hartman <gregkh@linux-foundation.org>,
	Tim Chen <tim.c.chen@linux.intel.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Kees Cook <keescook@google.com>, Rik van Riel <riel@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Andy Lutomirski <luto@amacapital.net>,
	Jiri Kosina <jikos@kernel.org>,
	One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>
Subject: Re: [PATCH v3 01/13] x86/retpoline: Add initial retpoline support
Date: Thu, 4 Jan 2018 10:36:01 -0800	[thread overview]
Message-ID: <20180104183559.wlqoxmp7rf4d44ku@ast-mbp> (raw)
In-Reply-To: <CA+55aFxRwAEe1VH-E_HMPf+jpxAUWaUkwLbJLXG2U44qHga+Dg@mail.gmail.com>

On Thu, Jan 04, 2018 at 10:25:35AM -0800, Linus Torvalds wrote:
> On Thu, Jan 4, 2018 at 10:17 AM, Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
> >
> > Clearly Paul's approach to retpoline without lfence is faster.
> > I'm guessing it wasn't shared with amazon/intel until now and
> > this set of patches going to adopt it, right?
> >
> > Paul, could you share a link to a set of alternative gcc patches
> > that do retpoline similar to llvm diff ?
> 
> What is the alternative approach? Is it literally just doing a
> 
>       call 1f
> 1:    mov real_target,(%rsp)
>        ret
> 
> on the assumption that the "ret" will always just predict to that "1"
> due to the call stack?

Pretty much.
Paul's writeup: https://support.google.com/faqs/answer/7625886
tldr: jmp *%r11 gets converted to:
call set_up_target;
capture_spec:
  pause;
  jmp capture_spec;
set_up_target:
  mov %r11, (%rsp);
  ret;
where capture_spec part will be looping speculatively.

  reply	other threads:[~2018-01-04 18:36 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 [this message]
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
2018-01-05 11:43       ` Woodhouse, David

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