linux-kernel - Re: [PATCH v9 02/29] x86/boot: Relocate definition of the initial state of CR0

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Date:   Fri, 27 Oct 2017 12:02:19 -0700
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     Borislav Petkov <bp@...e.de>
Cc:     Andy Lutomirski <luto@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Brian Gerst <brgerst@...il.com>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Huang Rui <ray.huang@....com>, Jiri Slaby <jslaby@...e.cz>,
        Jonathan Corbet <corbet@....net>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Chen Yucong <slaoub@...il.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Shuah Khan <shuah@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        X86 ML <x86@...nel.org>,
        "Neri, Ricardo" <ricardo.neri@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH v9 02/29] x86/boot: Relocate definition of the initial
 state of CR0

On Thu, Oct 26, 2017 at 02:55:13PM +0200, Borislav Petkov wrote:
> On Thu, Oct 26, 2017 at 02:02:02AM -0700, Andy Lutomirski wrote:
> > I'm assuming that UMIP_REPORTED_CR0 will never change.  If CR0 gets a
> > new field that we set some day, then I assume that CR0_STATE would add
> > that bit but UMIP_REPORTED_CR0 would not.
> 
> Yeah, let's do that when it is actually needed.

Thanks Andy! I reasoned that for UMIP could report CR0_STATE a value that
is already revealed in the source code. Thus, if CR0 ever changes at run
time, an attacker could only see what is set programmatically.

BR,

Ricardo