linux-kernel - Re: [PATCH v6 1/3] fork: Add generic vmalloced stack support

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Message-ID: <20160824100352.GA9681@gmail.com>
Date:   Wed, 24 Aug 2016 12:03:53 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Andy Lutomirski <luto@...nel.org>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Cc:     x86@...nel.org, Borislav Petkov <bp@...en8.de>,
        linux-kernel@...r.kernel.org, Brian Gerst <brgerst@...il.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH v6 1/3] fork: Add generic vmalloced stack support


* Andy Lutomirski <luto@...nel.org> wrote:

> +config VMAP_STACK
> +	default y
> +	bool "Use a virtually-mapped stack"
> +	depends on HAVE_ARCH_VMAP_STACK && !KASAN
> +	---help---
> +	  Enable this if you want the use virtually-mapped kernel stacks
> +	  with guard pages.  This causes kernel stack overflows to be
> +	  caught immediately rather than causing difficult-to-diagnose
> +	  corruption.
> +
> +	  This is presently incompatible with KASAN because KASAN expects
> +	  the stack to map directly to the KASAN shadow map using a formula
> +	  that is incorrect if the stack is in vmalloc space.

Btw., is this KASAN limitation fundamental?

As x86 is going to enable this feature by default, this probably limits KASAN 
utility rather significantly.

Thanks,

	Ingo