linux-kernel - Re: [PATCH 00/29] x86: Kernel IBT

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Date:   Mon, 21 Feb 2022 10:24:56 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
        "Poimboe, Josh" <jpoimboe@...hat.com>,
        "hjl.tools@...il.com" <hjl.tools@...il.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "joao@...rdrivepizza.com" <joao@...rdrivepizza.com>,
        "Cooper, Andrew" <andrew.cooper3@...rix.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "samitolvanen@...gle.com" <samitolvanen@...gle.com>,
        "ndesaulniers@...gle.com" <ndesaulniers@...gle.com>,
        "Milburn, Alyssa" <alyssa.milburn@...el.com>
Subject: Re: [PATCH 00/29] x86: Kernel IBT

On Mon, Feb 21, 2022 at 12:42:25AM -0800, Kees Cook wrote:

> >+void cet_disable(void)
> >+{
> >+	cr4_clear_bits(X86_CR4_CET);
> 
> I'd rather keep the pinning...

Uff. is that still enforced at this point?

> >+	wrmsrl(MSR_IA32_S_CET, 0);
> >+}
> 
> Eh, why not just require kexec to be IBT safe? That seems a reasonable
> exercise if we ever expect UEFI to enforce IBT when starting the
> kernel on a normal boot...

Well, it makes it impossible to kexec into an 'old' kernel. That might
not be very nice.