linux-kernel - Re: [PATCH v1] x86: Pin cr4 FSGSBASE

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Message-ID: <202005260918.72DE289@keescook>
Date:   Tue, 26 May 2020 09:20:31 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Andi Kleen <andi@...stfloor.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org, sashal@...nel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH v1] x86: Pin cr4 FSGSBASE

On Tue, May 26, 2020 at 08:48:35AM -0700, Andi Kleen wrote:
> On Tue, May 26, 2020 at 08:56:18AM +0200, Greg KH wrote:
> > On Mon, May 25, 2020 at 10:28:48PM -0700, Andi Kleen wrote:
> > > +		if (val & X86_CR4_FSGSBASE) {
> > > +			WARN_ONCE(1, "CR4 unexpectedly set FSGSBASE!?\n");
> > 
> > What about those systems that panic-on-warn?
> 
> I assume they're ok with "panic on root hole"

Exactly. :) The pinning infrastructure is pretty small; will that just
get backported? (Also, we can probably rework the pinning to avoid the
special-casing and use a mask/value pair to notice a bit getting turned
_on_ as well...)

-- 
Kees Cook