linux-kernel - Re: [PATCH v3] Documentation: Add section about CPU vulnerabilities for Spectre

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Date:   Mon, 17 Jun 2019 16:30:26 -0400
From:   Jon Masters <jcm@...hat.com>
To:     Tim Chen <tim.c.chen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Jonathan Corbet <corbet@....net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ben Greear <greearb@...delatech.com>, stable@...r.kernel.org,
        Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Jun Nakajima <jun.nakajima@...el.com>,
        Jiri Kosina <jikos@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        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>,
        Asit Mallick <asit.k.mallick@...el.com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Waiman Long <longman9394@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Mark Gross <mgross@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>, x86@...nel.org
Subject: Re: [PATCH v3] Documentation: Add section about CPU vulnerabilities
 for Spectre

On 6/17/19 4:22 PM, Jon Masters wrote:

>> +   For kernel code that has been identified where data pointers could
>> +   potentially be influenced for Spectre attacks, new "nospec" accessor
>> +   macros are used to prevent speculative loading of data.
> 
> Maybe explain that nospec (speculative clamping) relies on the absence
> of value prediction in the masking (in current hardware). It may NOT
> always be a safe approach in future hardware, where Spectre-v1 attacks
> are likely to persist but hardware may speculate about the mask value.

Something like the Arm CSDB barrier would seem to be potentially useful
for $FUTURE_X86 as a fence with lighter-weight semantics than an *fence.

Jon.

-- 
Computer Architect | Sent with my Fedora powered laptop