linux-kernel - Re: [PATCH v2 18/39] x86/ibt: Add IBT feature, MSR and #CP handling

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Message-ID: <Yh911I6Oh9RbCQz1@hirez.programming.kicks-ass.net>
Date:   Wed, 2 Mar 2022 14:49:08 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
Cc:     "keescook@...omium.org" <keescook@...omium.org>,
        "Poimboe, Josh" <jpoimboe@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Cooper, Andrew" <andrew.cooper3@...rix.com>,
        "hjl.tools@...il.com" <hjl.tools@...il.com>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "joao@...rdrivepizza.com" <joao@...rdrivepizza.com>,
        "samitolvanen@...gle.com" <samitolvanen@...gle.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "alexei.starovoitov@...il.com" <alexei.starovoitov@...il.com>,
        "Milburn, Alyssa" <alyssa.milburn@...el.com>,
        "mhiramat@...nel.org" <mhiramat@...nel.org>,
        "mbenes@...e.cz" <mbenes@...e.cz>,
        "ndesaulniers@...gle.com" <ndesaulniers@...gle.com>
Subject: Re: [PATCH v2 18/39] x86/ibt: Add IBT feature, MSR and #CP handling

On Wed, Mar 02, 2022 at 01:59:46AM +0000, Edgecombe, Rick P wrote:
> As for pinning strength, I'm not understanding this kexec asm enough to
> say for sure how much better it is than just removing the bit from the
> pinning mask. I think some future hardening around preventing turning
> off IBT might still be worthwhile.
> 
> Kees, I think you brought up the pinning, what do you think of this?

IIRC the whole purpose of that was to ensure that the
cr4_update_irqsoff() function itself isn't a useful gadget to manipulate
CR4 with.