linux-kernel - KASAN vs. boot-time switching between 4- and 5-level paging

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Date:   Sat, 27 May 2017 01:10:59 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Andy Lutomirski <luto@...capital.net>,
        linux-arch@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: KASAN vs. boot-time switching between 4- and 5-level paging

On Thu, May 25, 2017 at 11:33:33PM +0300, Kirill A. Shutemov wrote:
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 0bf81e837cbf..c795207d8a3c 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -100,7 +100,7 @@ config X86
>  	select HAVE_ARCH_AUDITSYSCALL
>  	select HAVE_ARCH_HUGE_VMAP		if X86_64 || X86_PAE
>  	select HAVE_ARCH_JUMP_LABEL
> -	select HAVE_ARCH_KASAN			if X86_64 && SPARSEMEM_VMEMMAP
> +	select HAVE_ARCH_KASAN			if X86_64 && SPARSEMEM_VMEMMAP && !X86_5LEVEL
>  	select HAVE_ARCH_KGDB
>  	select HAVE_ARCH_KMEMCHECK
>  	select HAVE_ARCH_MMAP_RND_BITS		if MMU

Looks like KASAN will be a problem for boot-time paging mode switching.
It wants to know CONFIG_KASAN_SHADOW_OFFSET at compile-time to pass to
gcc -fasan-shadow-offset=. But this value varies between paging modes...

I don't see how to solve it. Folks, any ideas?

-- 
 Kirill A. Shutemov