All of lore.kernel.org
 help / color / mirror / Atom feed
From: Brian Gerst <brgerst@gmail.com>
To: "Woodhouse, David" <dwmw@amazon.co.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	"bp@suse.de" <bp@suse.de>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"peterz@infradead.org" <peterz@infradead.org>,
	"tim.c.chen@linux.intel.com" <tim.c.chen@linux.intel.com>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	"ak@linux.intel.com" <ak@linux.intel.com>,
	"riel@redhat.com" <riel@redhat.com>,
	"keescook@google.com" <keescook@google.com>,
	"gnomes@lxorguk.ukuu.org.uk" <gnomes@lxorguk.ukuu.org.uk>,
	"pjt@google.com" <pjt@google.com>,
	"dave.hansen@intel.com" <dave.hansen@intel.com>,
	"luto@amacapital.net" <luto@amacapital.net>,
	"jikos@kernel.org" <jikos@kernel.org>,
	"gregkh@linux-foundation.org" <gregkh@linux-foundation.org>
Subject: Re: [PATCH v3 01/13] x86/retpoline: Add initial retpoline support
Date: Fri, 5 Jan 2018 16:11:07 -0500	[thread overview]
Message-ID: <CAMzpN2jN_n3_GbHgT5kOiSQNcGVwAM16HDxPs7qqe56Kw-i6XQ@mail.gmail.com> (raw)
In-Reply-To: <1515184364.29312.188.camel@amazon.co.uk>

On Fri, Jan 5, 2018 at 3:32 PM, Woodhouse, David <dwmw@amazon.co.uk> wrote:
> On Fri, 2018-01-05 at 09:28 -0800, Linus Torvalds wrote:
>>
>> Yes, I would suggest against expecting altinstructions to have
>> relocation information. They are generated in a different place, so..
>>
>> That said, I honestly like the inline version (the one that is in the
>> google paper first) of the retpoline more than the out-of-line one.
>> And that one shouldn't have any relocation issues, because all the
>> offsets are relative.
>
> Note that the *only* issue with the relocation is that it pushes me to
> use X86_FEATURE_NO_RETPOLINE for my feature instead of
> X86_FEATURE_RETPOLINE as might be natural. And actually there's a
> motivation to do that anyway, because of the way three-way alternatives
> interact.
>
> With the existing negative flag I can do
>
>  ALTERNATIVE_2(retpoline, K8: lfence+jmp; NO_RETPOLINE: jmp)
>
> But if I invert it, I think I need two feature flags to get the same functionality — X86_FEATURE_RETPOLINE and X86_FEATURE_RETPOLINE_AMD:
>
>  ALTERNATIVE_2(jmp, RETPOLINE: retpoline, RETPOLINE_AMD: lfence+jmp)

Another way to do it is with two consecutive alternatives:

ALTERNATIVE(NOP, K8: lfence)
ALTERNATIVE(jmp indirect, RETPOLINE: jmp thunk)

This also avoids the issue with the relocation of the jmp target when
the replacement is more than one instruction.

--
Brian Gerst

  reply	other threads:[~2018-01-05 21:11 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 [this message]
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

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=CAMzpN2jN_n3_GbHgT5kOiSQNcGVwAM16HDxPs7qqe56Kw-i6XQ@mail.gmail.com \
    --to=brgerst@gmail.com \
    --cc=ak@linux.intel.com \
    --cc=bp@suse.de \
    --cc=dave.hansen@intel.com \
    --cc=dwmw@amazon.co.uk \
    --cc=gnomes@lxorguk.ukuu.org.uk \
    --cc=gregkh@linux-foundation.org \
    --cc=jikos@kernel.org \
    --cc=keescook@google.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=luto@amacapital.net \
    --cc=peterz@infradead.org \
    --cc=pjt@google.com \
    --cc=riel@redhat.com \
    --cc=tglx@linutronix.de \
    --cc=tim.c.chen@linux.intel.com \
    --cc=torvalds@linux-foundation.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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.