linux-kernel - Re: [tip:x86/pti] x86/retpoline: Fill RSB on context switch for affected CPUs

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Message-ID: <CAGXu5jK=-9oQPPxtjU0wKRyae2W=M2TP4zJaY3RwcrRvQ1Efnw@mail.gmail.com>
Date:   Mon, 15 Jan 2018 12:03:45 -0800
From:   Kees Cook <keescook@...gle.com>
To:     Arjan van de Ven <arjan@...ux.intel.com>
Cc:     David Laight <David.Laight@...lab.com>,
        "dwmw@...zon.co.uk" <dwmw@...zon.co.uk>,
        "riel@...hat.com" <riel@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "tim.c.chen@...ux.intel.com" <tim.c.chen@...ux.intel.com>,
        "pjt@...gle.com" <pjt@...gle.com>,
        "jpoimboe@...hat.com" <jpoimboe@...hat.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "gregkh@...ux-foundation.org" <gregkh@...ux-foundation.org>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        "dave.hansen@...el.com" <dave.hansen@...el.com>,
        "luto@...capital.net" <luto@...capital.net>,
        "jikos@...nel.org" <jikos@...nel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "mingo@...nel.org" <mingo@...nel.org>,
        "hpa@...or.com" <hpa@...or.com>,
        "linux-tip-commits@...r.kernel.org" 
        <linux-tip-commits@...r.kernel.org>
Subject: Re: [tip:x86/pti] x86/retpoline: Fill RSB on context switch for
 affected CPUs

On Mon, Jan 15, 2018 at 6:42 AM, Arjan van de Ven <arjan@...ux.intel.com> wrote:
>>
>> This would means that userspace would see return predictions based
>> on the values the kernel 'stuffed' into the RSB to fill it.
>>
>> Potentially this leaks a kernel address to userspace.
>
>
> KASLR pretty much died in May this year to be honest with the KAISER paper
> (if not before then)

KASLR was always on shaky ground for local attacks. For pure remote
attacks, it's still useful. And for driving forward research, it
appears to be quite useful. ;)

-Kees

-- 
Kees Cook
Pixel Security