linux-kernel - Re: Bug report about KASLR and ZONE

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Date:   Thu, 12 Jul 2018 14:32:28 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Chao Fan <fanc.fnst@...fujitsu.com>
Cc:     Dou Liyang <douly.fnst@...fujitsu.com>,
        Baoquan He <bhe@...hat.com>, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org, x86@...nel.org,
        yasu.isimatu@...il.com, keescook@...omium.org,
        indou.takao@...fujitsu.com, caoj.fnst@...fujitsu.com,
        vbabka@...e.cz, mgorman@...hsingularity.net
Subject: Re: Bug report about KASLR and ZONE_MOVABLE

On Thu 12-07-18 14:01:15, Chao Fan wrote:
> On Thu, Jul 12, 2018 at 01:49:49PM +0800, Dou Liyang wrote:
> >Hi Baoquan,
> >
> >At 07/11/2018 08:40 PM, Baoquan He wrote:
> >> Please try this v3 patch:
> >> >>From 9850d3de9c02e570dc7572069a9749a8add4c4c7 Mon Sep 17 00:00:00 2001
> >> From: Baoquan He <bhe@...hat.com>
> >> Date: Wed, 11 Jul 2018 20:31:51 +0800
> >> Subject: [PATCH v3] mm, page_alloc: find movable zone after kernel text
> >> 
> >> In find_zone_movable_pfns_for_nodes(), when try to find the starting
> >> PFN movable zone begins in each node, kernel text position is not
> >> considered. KASLR may put kernel after which movable zone begins.
> >> 
> >> Fix it by finding movable zone after kernel text on that node.
> >> 
> >> Signed-off-by: Baoquan He <bhe@...hat.com>
> >
> >
> >You fix this in the _zone_init side_. This may make the 'kernelcore=' or
> >'movablecore=' failed if the KASLR puts the kernel back the tail of the
> >last node, or more.
> 
> I think it may not fail.
> There is a 'restart' to do another pass.
> 
> >
> >Due to we have fix the mirror memory in KASLR side, and Chao is trying
> >to fix the 'movable_node' in KASLR side. Have you had a chance to fix
> >this in the KASLR side.
> >
> 
> I think it's better to fix here, but not KASLR side.
> Cause much more code will be change if doing it in KASLR side.
> Since we didn't parse 'kernelcore' in compressed code, and you can see
> the distribution of ZONE_MOVABLE need so much code, so we do not need
> to do so much job in KASLR side. But here, several lines will be OK.

I am not able to find the beginning of the email thread right now. Could
you summarize what is the actual problem please?
-- 
Michal Hocko
SUSE Labs