linux-kernel - Re: [PATCHv2] x86/alternatives: Disable KASAN in apply

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Date:   Wed, 11 Oct 2023 11:37:25 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org,
        Fei Yang <fei.yang@...el.com>, stable@...r.kernel.org
Subject: Re: [PATCHv2] x86/alternatives: Disable KASAN in apply_alternatives()

On Wed, Oct 11, 2023 at 10:11:46AM +0200, Ingo Molnar wrote:
> 
> * Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > >  	DPRINTK(ALT, "alt table %px, -> %px", start, end);
> > > +
> > > +	/*
> > > +	 * In the case CONFIG_X86_5LEVEL=y, KASAN_SHADOW_START is defined using
> > > +	 * cpu_feature_enabled(X86_FEATURE_LA57) and is therefore patched here.
> > > +	 * During the process, KASAN becomes confused and triggers
> > 
> > 	because of partial LA57 convertion ..
> 
> Not all LA57 related sites are patched yet at this point, and KASAN sees
> a weird & broken mixture of LA48 and LA57 runtime semantics, right?
> 
> Ie. as far as KASAN is concerned, the LA48 -> LA57 behavioral switchover
> must be atomic, but during the kernel code patching process it isn't.

Yep, half-way through the patching it observes inconsistencies and goes
WTF :-)