LKML Archive on lore.kernel.org
 help / color / Atom feed
From: Andi Kleen <ak@linux.intel.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
	x86@kernel.org, Peter Zijlstra <peterz@infradead.org>,
	Andy Lutomirski <luto@kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Jiri Kosina <jkosina@suse.cz>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	David Woodhouse <dwmw@amazon.co.uk>,
	Tim Chen <tim.c.chen@linux.intel.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Casey Schaufler <casey.schaufler@intel.com>,
	Asit Mallick <asit.k.mallick@intel.com>,
	Arjan van de Ven <arjan@linux.intel.com>,
	Jon Masters <jcm@redhat.com>, Waiman Long <longman9394@gmail.com>,
	Greg KH <gregkh@linuxfoundation.org>,
	Dave Stewart <david.c.stewart@intel.com>,
	Kees Cook <keescook@chromium.org>
Subject: Re: [patch V2 21/28] x86/speculation: Prepare for conditional IBPB in switch_mm()
Date: Sun, 25 Nov 2018 12:53:30 -0800
Message-ID: <20181125205330.GO13936@tassilo.jf.intel.com> (raw)
In-Reply-To: <20181125185005.466447057@linutronix.de>

> The current check whether two tasks belong to the same context is using the
> tasks context id. While correct, it's simpler to use the mm pointer because
> it allows to mangle the TIF_SPEC_IB bit into it. The context id based
> mechanism requires extra storage, which creates worse code.

[We tried similar in some really early versions, but it was replaced
with the context id later.]

One issue with using the pointer is that the pointer can be reused
when the original mm_struct is freed, and then gets reallocated
immediately to an attacker. Then the attacker may avoid the IBPB.

Given it's probably hard to generate any reasonable leak bandwidth with
such a complex scenario, but it still seemed better to close the hole.

Because of concerns with that the counter ID was used instead.

The ID can wrap too, but since it's 64bit, it will take very long.

-Andi


  parent reply index

Thread overview: 112+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-25 18:33 [patch V2 00/28] x86/speculation: Remedy the STIBP/IBPB overhead Thomas Gleixner
2018-11-25 18:33 ` [patch V2 01/28] x86/speculation: Update the TIF_SSBD comment Thomas Gleixner
2018-11-28 14:20   ` [tip:x86/pti] " tip-bot for Tim Chen
2018-11-29 14:27   ` [patch V2 01/28] " Konrad Rzeszutek Wilk
2018-11-25 18:33 ` [patch V2 02/28] x86/speculation: Clean up spectre_v2_parse_cmdline() Thomas Gleixner
2018-11-28 14:20   ` [tip:x86/pti] " tip-bot for Tim Chen
2018-11-29 14:28   ` [patch V2 02/28] " Konrad Rzeszutek Wilk
2018-11-25 18:33 ` [patch V2 03/28] x86/speculation: Remove unnecessary ret variable in cpu_show_common() Thomas Gleixner
2018-11-28 14:21   ` [tip:x86/pti] " tip-bot for Tim Chen
2018-11-29 14:28   ` [patch V2 03/28] " Konrad Rzeszutek Wilk
2018-11-25 18:33 ` [patch V2 04/28] x86/speculation: Reorganize cpu_show_common() Thomas Gleixner
2018-11-26 15:08   ` Borislav Petkov
2018-11-28 14:22   ` [tip:x86/pti] x86/speculation: Move STIPB/IBPB string conditionals out of cpu_show_common() tip-bot for Tim Chen
2018-11-29 14:29   ` [patch V2 04/28] x86/speculation: Reorganize cpu_show_common() Konrad Rzeszutek Wilk
2018-11-25 18:33 ` [patch V2 05/28] x86/speculation: Disable STIBP when enhanced IBRS is in use Thomas Gleixner
2018-11-28 14:22   ` [tip:x86/pti] " tip-bot for Tim Chen
2018-11-29 14:35   ` [patch V2 05/28] " Konrad Rzeszutek Wilk
2018-11-25 18:33 ` [patch V2 06/28] x86/speculation: Rename SSBD update functions Thomas Gleixner
2018-11-26 15:24   ` Borislav Petkov
2018-11-28 14:23   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-29 14:37   ` [patch V2 06/28] " Konrad Rzeszutek Wilk
2018-11-25 18:33 ` [patch V2 07/28] x86/speculation: Reorganize speculation control MSRs update Thomas Gleixner
2018-11-26 15:47   ` Borislav Petkov
2018-11-28 14:23   ` [tip:x86/pti] " tip-bot for Tim Chen
2018-11-29 14:41   ` [patch V2 07/28] " Konrad Rzeszutek Wilk
2018-11-25 18:33 ` [patch V2 08/28] sched/smt: Make sched_smt_present track topology Thomas Gleixner
2018-11-28 14:24   ` [tip:x86/pti] " tip-bot for Peter Zijlstra (Intel)
2018-11-29 14:42   ` [patch V2 08/28] " Konrad Rzeszutek Wilk
2018-11-29 14:50     ` Konrad Rzeszutek Wilk
2018-11-29 15:48       ` Peter Zijlstra
2018-11-25 18:33 ` [patch V2 09/28] x86/Kconfig: Select SCHED_SMT if SMP enabled Thomas Gleixner
2018-11-28 14:24   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-29 14:44   ` [patch V2 09/28] " Konrad Rzeszutek Wilk
2018-11-25 18:33 ` [patch V2 10/28] sched/smt: Expose sched_smt_present static key Thomas Gleixner
2018-11-28 14:25   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-29 14:44   ` [patch V2 10/28] " Konrad Rzeszutek Wilk
2018-11-25 18:33 ` [patch V2 11/28] x86/speculation: Rework SMT state change Thomas Gleixner
2018-11-28 14:26   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-25 18:33 ` [patch V2 12/28] x86/l1tf: Show actual SMT state Thomas Gleixner
2018-11-28 14:26   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-25 18:33 ` [patch V2 13/28] x86/speculation: Reorder the spec_v2 code Thomas Gleixner
2018-11-26 22:21   ` Borislav Petkov
2018-11-28 14:27   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-25 18:33 ` [patch V2 14/28] x86/speculation: Mark string arrays const correctly Thomas Gleixner
2018-11-28 14:27   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-25 18:33 ` [patch V2 15/28] x86/speculataion: Mark command line parser data __initdata Thomas Gleixner
2018-11-28 14:28   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-25 18:33 ` [patch V2 16/28] x86/speculation: Unify conditional spectre v2 print functions Thomas Gleixner
2018-11-28 14:29   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-25 18:33 ` [patch V2 17/28] x86/speculation: Add command line control for indirect branch speculation Thomas Gleixner
2018-11-28 14:29   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-25 18:33 ` [patch V2 18/28] x86/speculation: Prepare for per task indirect branch speculation control Thomas Gleixner
2018-11-27 17:25   ` Lendacky, Thomas
2018-11-27 19:51     ` Tim Chen
2018-11-28  9:39       ` Thomas Gleixner
2018-11-27 20:39     ` Thomas Gleixner
2018-11-27 20:42       ` Thomas Gleixner
2018-11-27 21:52         ` Lendacky, Thomas
2018-11-28 14:30   ` [tip:x86/pti] " tip-bot for Tim Chen
2018-11-25 18:33 ` [patch V2 19/28] x86/process: Consolidate and simplify switch_to_xtra() code Thomas Gleixner
2018-11-26 18:30   ` Borislav Petkov
2018-11-28 14:30   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-25 18:33 ` [patch V2 20/28] x86/speculation: Avoid __switch_to_xtra() calls Thomas Gleixner
2018-11-28 14:31   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-25 18:33 ` [patch V2 21/28] x86/speculation: Prepare for conditional IBPB in switch_mm() Thomas Gleixner
2018-11-25 19:11   ` Thomas Gleixner
2018-11-25 20:53   ` Andi Kleen [this message]
2018-11-25 22:20     ` Thomas Gleixner
2018-11-25 23:04       ` Andy Lutomirski
2018-11-26  7:10         ` Thomas Gleixner
2018-11-26 13:36           ` Ingo Molnar
2018-11-26  3:07       ` Andi Kleen
2018-11-26  6:50         ` Thomas Gleixner
2018-11-28 14:31   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-25 18:33 ` [patch V2 22/28] ptrace: Remove unused ptrace_may_access_sched() and MODE_IBRS Thomas Gleixner
2018-11-28 14:32   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-25 18:33 ` [patch V2 23/28] x86/speculation: Split out TIF update Thomas Gleixner
2018-11-28 14:33   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-25 18:33 ` [patch V2 24/28] x86/speculation: Prepare arch_smt_update() for PRCTL mode Thomas Gleixner
2018-11-27 20:18   ` Lendacky, Thomas
2018-11-27 20:30     ` Thomas Gleixner
2018-11-27 21:20       ` Lendacky, Thomas
2018-11-28 14:34   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-25 18:33 ` [patch V2 25/28] x86/speculation: Add prctl() control for indirect branch speculation Thomas Gleixner
2018-11-28 14:34   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-25 18:33 ` [patch V2 26/28] x86/speculation: Enable prctl mode for spectre_v2_user Thomas Gleixner
2018-11-26  7:56   ` Dominik Brodowski
2018-11-28 14:35   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-25 18:33 ` [patch V2 27/28] x86/speculation: Add seccomp Spectre v2 user space protection mode Thomas Gleixner
2018-11-25 19:35   ` Randy Dunlap
2018-11-25 20:40   ` Linus Torvalds
2018-11-25 20:52     ` Jiri Kosina
2018-11-25 22:28     ` Thomas Gleixner
2018-11-26 13:30       ` Ingo Molnar
2018-11-26 20:48       ` Andrea Arcangeli
2018-11-26 20:58         ` Thomas Gleixner
2018-11-26 21:52           ` Lendacky, Thomas
2018-11-27  0:37             ` Tim Chen
2018-12-04  1:38     ` Tim Chen
2018-12-04  8:39       ` Jiri Kosina
2018-12-04  9:43         ` Arjan van de Ven
2018-12-04  9:46         ` Arjan van de Ven
2018-12-04 17:20       ` Linus Torvalds
2018-12-04 18:58         ` Tim Chen
2018-11-28 14:35   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-12-04 18:45   ` [patch V2 27/28] " Dave Hansen
2018-11-25 18:33 ` [patch V2 28/28] x86/speculation: Provide IBPB always command line options Thomas Gleixner
2018-11-28 14:36   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-26 13:37 ` [patch V2 00/28] x86/speculation: Remedy the STIBP/IBPB overhead Ingo Molnar
2018-11-28 14:24 ` Thomas Gleixner
2018-11-29 19:02   ` Tim Chen
2018-12-10 23:43 ` Pavel Machek

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=20181125205330.GO13936@tassilo.jf.intel.com \
    --to=ak@linux.intel.com \
    --cc=aarcange@redhat.com \
    --cc=arjan@linux.intel.com \
    --cc=asit.k.mallick@intel.com \
    --cc=casey.schaufler@intel.com \
    --cc=dave.hansen@intel.com \
    --cc=david.c.stewart@intel.com \
    --cc=dwmw@amazon.co.uk \
    --cc=gregkh@linuxfoundation.org \
    --cc=jcm@redhat.com \
    --cc=jkosina@suse.cz \
    --cc=jpoimboe@redhat.com \
    --cc=keescook@chromium.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=longman9394@gmail.com \
    --cc=luto@kernel.org \
    --cc=peterz@infradead.org \
    --cc=tglx@linutronix.de \
    --cc=thomas.lendacky@amd.com \
    --cc=tim.c.chen@linux.intel.com \
    --cc=torvalds@linux-foundation.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

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git
	git clone --mirror https://lore.kernel.org/lkml/8 lkml/git/8.git
	git clone --mirror https://lore.kernel.org/lkml/9 lkml/git/9.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org
	public-inbox-index lkml

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git