linux-kernel - Re: [PATCH 23/35] x86/speculation: Add basic speculation control code

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Date:   Thu, 18 Jan 2018 23:35:36 +0000
From:   Andrew Cooper <andrew.cooper3@...rix.com>
To:     Andy Lutomirski <luto@...nel.org>,
        Andrea Arcangeli <aarcange@...hat.com>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Ashok Raj <ashok.raj@...el.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Arjan Van De Ven <arjan.van.de.ven@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Jun Nakajima <jun.nakajima@...el.com>,
        Asit Mallick <asit.k.mallick@...el.com>,
        Jason Baron <jbaron@...mai.com>
Subject: Re: [PATCH 23/35] x86/speculation: Add basic speculation control code

On 18/01/2018 23:25, Andy Lutomirski wrote:
> On Thu, Jan 18, 2018 at 11:08 AM, Andrea Arcangeli <aarcange@...hat.com> wrote:
>> On Thu, Jan 18, 2018 at 12:24:31PM -0600, Josh Poimboeuf wrote:
>>> On Thu, Jan 18, 2018 at 06:12:36PM +0100, Paolo Bonzini wrote:
>>>> On 18/01/2018 18:08, Dave Hansen wrote:
>>>>> On 01/18/2018 08:37 AM, Josh Poimboeuf wrote:
>>>>>>> --- a/Documentation/admin-guide/kernel-parameters.txt
>>>>>>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>>>>>>> @@ -3932,6 +3932,7 @@
>>>>>>>                         retpoline         - replace indirect branches
>>>>>>>                         retpoline,generic - google's original retpoline
>>>>>>>                         retpoline,amd     - AMD-specific minimal thunk
>>>>>>> +                       ibrs              - Intel: Indirect Branch Restricted Speculation
>>>>>> Are there plans to add spectre_v2=ibrs_always to prevent SMT-based
>>>>>> attacks?
>>>>> What does "ibrs_always" mean to you?
>>> Maybe ibrs_always isn't the best name.  Basically we need an option to
>>> protect user-user attacks via SMT.
>>>
>>> It could be implemented with IBRS=1, or STIBP, or as part of the
>>> mythical IBRS_ATT.
>> User stibp or user ibrs would be different things, both would be valid
>> for different use cases, and the user stibp should perform better.
>>
>> Leaving ibrs on when returning from kernel to userland (or setting
>> ibrs if kernel used retpolines instead of ibrs) achieves stronger
>> semantics than just setting SPEC_CTRL with stibp when returning to
>> userland.
> I read the whitepaper that documented the new MSRs a couple days ago
> and I'm now completely unable to find it.  If anyone could send the
> link, that would be great.

https://software.intel.com/sites/default/files/managed/c5/63/336996-Speculative-Execution-Side-Channel-Mitigations.pdf

~Andrew