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

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Message-ID: <20200526163235.GA42137@kroah.com>
Date:   Tue, 26 May 2020 18:32:35 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     Andi Kleen <andi@...stfloor.org>, x86@...nel.org,
        keescook@...omium.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:
> > > From: Andi Kleen <ak@...ux.intel.com>
> > > 
> > > Since there seem to be kernel modules floating around that set
> > > FSGSBASE incorrectly, prevent this in the CR4 pinning. Currently
> > > CR4 pinning just checks that bits are set, this also checks
> > > that the FSGSBASE bit is not set, and if it is clears it again.
> > 
> > So we are trying to "protect" ourselves from broken out-of-tree kernel
> > modules now?  
> 
> Well it's a specific case where we know they're opening a root hole
> unintentionally. This is just an pragmatic attempt to protect the users in the 
> short term.

Can't you just go and fix those out-of-tree kernel modules instead?
What's keeping you all from just doing that instead of trying to force
the kernel to play traffic cop?

thanks,

greg k-h