Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH] x86/cpuid: Fix up "virtual" IBRS/IBPB/STIBP feature bits
 on Intel
To:     Borislav Petkov <bp@alien8.de>,
        Thomas Gleixner <tglx@linutronix.de>
Cc:     David Woodhouse <dwmw2@infradead.org>, karahmed@amazon.de,
        x86@kernel.org, linux-kernel@vger.kernel.org,
        tim.c.chen@linux.intel.com, peterz@infradead.org,
        pbonzini@redhat.com, ak@linux.intel.com,
        torvalds@linux-foundation.org, gregkh@linux-foundation.org
References: <1517269773-16750-1-git-send-email-dwmw@amazon.co.uk>
 <20180130105814.m5zd43dyx2o2ius2@pd.tnic>
 <1517310230.18619.86.camel@infradead.org>
 <20180130111848.zjv2dngfzcz35lyt@pd.tnic>
 <1517311693.18619.102.camel@infradead.org>
 <alpine.DEB.2.20.1801301235500.1797@nanos>
 <1517314193.18619.115.camel@infradead.org>
 <alpine.DEB.2.20.1801301349140.1797@nanos>
 <20180130131122.s3bs6lbs43go73gj@pd.tnic>
From:   Arjan van de Ven <arjan@linux.intel.com>
Message-ID: <37c4e2a7-6e35-d736-dfaf-83fbe4895401@linux.intel.com>
Date:   Tue, 30 Jan 2018 06:01:43 -0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101
 Thunderbird/52.5.2
MIME-Version: 1.0
In-Reply-To: <20180130131122.s3bs6lbs43go73gj@pd.tnic>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 1/30/2018 5:11 AM, Borislav Petkov wrote:
> On Tue, Jan 30, 2018 at 01:57:21PM +0100, Thomas Gleixner wrote:
>> So much for the theory. That's not going to work. If the boot cpu has the
>> feature then the alternatives will have been applied. So even if the flag
>> mismatch can be observed when a secondary CPU comes up the outcome will be
>> access to a non existing MSR and #GP.
> 
> Yes, with mismatched microcode we're f*cked.

I think in the super early days of SMP there was an occasional broken BIOS.
(and when Linux then did the ucode update it was sane again)

Not since a long time though (I think the various certification suites check for it now)

> 
> So my question is: is there such microcode out there or is this
> something theoretical which we want to address?

at this point it's insane theoretical; no OS can actually cope with this, so
if you're an OEM selling this, your customer can run zero OSes ;-)


> 
> (.. and adressing this will be ugly, no matter what.)
> 
> And if I were able to wish, I'd like to blacklist that microcode in
> dracut so that it doesn't come anywhere near my system.

I'm not sure what you'd want dracut to do... panic() the system
on such a bios?