linux-kernel - Re: kasan_map_early

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Date:	Tue, 03 Mar 2015 16:15:06 +0300
From:	Andrey Ryabinin <a.ryabinin@...sung.com>
To:	"Luis R. Rodriguez" <mcgrof@...e.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	xen-devel@...ts.xenproject.org,
	Andy Lutomirski <luto@...capital.net>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Chris Wright <chrisw@...s-sol.org>,
	Alok Kataria <akataria@...are.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	virtualization@...ts.linux-foundation.org
Subject: Re: kasan_map_early_shadow() on Xen

On 03/03/2015 12:40 PM, Luis R. Rodriguez wrote:
> Andrey,
> 
> I believe that on Xen we should disable kasan, would like confirmation

I guess Xen guests won't work with kasan because Xen guests doesn't setup shadow
(kasan_map_early_shadow() is not called in xen guests).

Disabling kasan for Xen in Kconfig is undesirable because that will disable kasan
for allmodconfig and allyesconfig builds, but I don't see other option for now.


> from someone on xen-devel though. Here's the thing though -- if true
> -- I'd like to do it *properly*, where *properly* means addressing a
> bit of architecture. A simple Kconfig slap seems rather reactive. I'd
> like to address a way to properly ensure we don't run into this and
> other similar issues in the future. The CR4 shadow issue was another
> recent example issue, also introduced via v4.0 [0]. We can't keep
> doing this reactively.
> 
> Let's go down the rabbit hole for a bit. HAVE_ARCH_KASAN will be
> selected on x86 when:
> 
> if X86_64 && SPARSEMEM_VMEMMAP
> 
> Now Xen should not have SPARSEMEM_VMEMMAP but PVOPs' goal is to enable
> distributions to be able to have a single binary kernels and let the
> rest be figured out, so we can't just disable SPARSEMEM_VMEMMAP for
> Xen alone, we want to build Xen.. or part of Xen and perhaps keep
> SPARSEMEM_VMEMMAP, and only later figure things out.
> 
> How do we do this cleanly and avoid future reactive measures? If the
> answer is not upon us, I'd like to at least highlight the issue so
> that in case we do come up with something its no surprise PVOPs is
> falling short for that single binary pipe dream right now.
> 
> [0] https://lkml.org/lkml/2015/2/23/328
> 
>  Luis
> 

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