linux-kernel - Re: [PATCH] x86/asm: Move native_write

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Message-ID: <20190710200240.GR3402@hirez.programming.kicks-ass.net>
Date:   Wed, 10 Jul 2019 22:02:40 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Xi Ruoyao <xry111@...gyan1223.wang>,
        Jiri Kosina <jikos@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Borislav Petkov <bp@...en8.de>, Len Brown <lenb@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Bob Moore <robert.moore@...el.com>,
        Erik Schmauss <erik.schmauss@...el.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Juergen Gross <jgross@...e.com>
Subject: Re: [PATCH] x86/asm: Move native_write_cr0/3() out of line

On Wed, Jul 10, 2019 at 09:42:46PM +0200, Thomas Gleixner wrote:
> The pinning of sensitive CR0 and CR4 bits caused a boot crash when loading
> the kvm_intel module on a kernel compiled with CONFIG_PARAVIRT=n.
> 
> The reason is that the static key which controls the pinning is marked RO
> after init. The kvm_intel module contains a CR4 write which requires to
> update the static key entry list. That obviously does not work when the key
> is in a RO section.
> 
> With CONFIG_PARAVIRT enabled this does not happen because the CR4 write
> uses the paravirt indirection and the actual write function is built in.
> 
> As the key is intended to be immutable after init, move
> native_write_cr0/3() out of line.
> 
> While at it consolidate the update of the cr4 shadow variable and store the
> value right away when the pinning is initialized on a booting CPU. No point
> in reading it back 20 instructions later. This allows to confine the static
> key and the pinning variable to cpu/common and allows to mark them static.
> 
> Fixes: 8dbec27a242c ("x86/asm: Pin sensitive CR0 bits")
> Fixes: 873d50d58f67 ("x86/asm: Pin sensitive CR4 bits")
> Reported-by: Linus Torvalds <torvalds@...ux-foundation.org>
> Reported-by: Xi Ruoyao <xry111@...gyan1223.wang>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Tested-by: Xi Ruoyao <xry111@...gyan1223.wang>

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>