linux-kernel - Re: [PATCH 0/2] Provide options to enable spectre

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Date:   Thu, 20 Sep 2018 21:38:59 +0000
From:   "Lendacky, Thomas" <Thomas.Lendacky@....com>
To:     Tim Chen <tim.c.chen@...ux.intel.com>,
        Jiri Kosina <jikos@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
CC:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Casey Schaufler <casey.schaufler@...el.com>,
        Asit Mallick <asit.k.mallick@...el.com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Jon Masters <jcm@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH 0/2] Provide options to enable spectre_v2
 userspace-userspace protection

On 09/19/2018 04:35 PM, Tim Chen wrote:
> This patchset provides an option to apply IBPB and STIBP mitigation
> to only non-dumpable processes.
> 
> Jiri's patch to harden spectre_v2 makes IBPB and STIBP available for
> general spectre v2 app to app mitigation.  IBPB will be issued for
> switching to an app that's not ptraceable by the previous
> app and STIBP will be always turned on.
> 
> However, leaving STIBP on all the time is expensive for certain
> applications that have frequent indirect branches. One such application
> is perlbench in the SpecInt Rate 2006 test suite which shows a
> 21% reduction in throughput.  Other application like bzip2 in
> the same test suite with  minimal indirct branches have
> only a 0.7% reduction in throughput. IBPB will also impose
> overhead during context switches.
> 
> App to app exploit is in general difficult
> due to address space layout randomization in apps and
> the need to know an app's address space layout ahead of time.
> Users may not wish to incur app to app performance
> overhead from IBPB and STIBP for general non security sensitive apps
> and use these mitigations only for non-dumpable apps.
> 
> The first patch provides a lite option for spectre_v2 app to app
> mitigation where IBPB is only issued for security sensitive
> non-dumpable app.  The second patch extends this option
> where STIBP is only issued for non-dumpable app.
> 
> The changes apply to intel cpus affected by spectre_v2. Tom,
> can you update the STIBP changes for AMD cpus on  
> __speculative_store_bypass_update and x86_virt_spec_ctrl
> to update the SPEC_CTRL msr for AMD cpu?

Hi Tim,

Let me think about this a bit, since it can get a bit tricky if
I want to avoid multiple MSR writes when only one may have been
needed (assuming SSBD is not using the SPEC_CTRL MSR).

Thanks,
Tom

> 
> Thanks.
> 
> Tim
> 
> Tim Chen (2):
>   x86/speculation: Option to select app to app mitigation for spectre_v2
>   x86/speculation: Provide application property based STIBP protection
> 
>  Documentation/admin-guide/kernel-parameters.txt |  11 +++
>  arch/x86/include/asm/msr-index.h                |   3 +-
>  arch/x86/include/asm/nospec-branch.h            |   9 ++
>  arch/x86/include/asm/spec-ctrl.h                |  12 +++
>  arch/x86/include/asm/thread_info.h              |   4 +-
>  arch/x86/kernel/cpu/bugs.c                      | 105 ++++++++++++++++++++++--
>  arch/x86/kernel/process.c                       |   9 +-
>  arch/x86/mm/tlb.c                               |  41 ++++++++-
>  8 files changed, 179 insertions(+), 15 deletions(-)
>