linux-kernel - Re: [RFC][PATCH 0/2] x86/boot/KASLR: Restrict kernel to be randomized in mirror regions if existed

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Date:   Thu, 15 Jun 2017 17:20:32 +0800
From:   'Baoquan He' <bhe@...hat.com>
To:     "Izumi, Taku" <izumi.taku@...fujitsu.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "Fan, Chao" <fanc.fnst@...fujitsu.com>,
        "Cao, Jin" <caoj.fnst@...fujitsu.com>,
        "Dou, Liyang" <douly.fnst@...fujitsu.com>
Subject: Re: [RFC][PATCH 0/2] x86/boot/KASLR: Restrict kernel to be
 randomized in mirror regions if existed

On 06/15/17 at 08:34am, Izumi, Taku wrote:
> Dear Baoquan,
> 
> > > Our customer reported that Kernel text may be located on non-mirror
> > > region (movable zone) when both address range mirroring feature and
> > > KASLR are enabled.
> 
>    I know your customer :)

LOL, have to agree.

> > > The method is very simple. If efi is enabled, just iterate all efi
> > > memory map and pick up mirror region to process for adding candidate
> > > of slot. If efi disabled or no mirror region existed, still process
> > > e820 memory map. This won't bring much efficiency loss, at worst we
> > > just go through all efi memory maps and found no mirror.
> > >
> > > One question:
> > > From code, though mirror regions are existed, they are meaningful only
> > > if kernelcore=mirror kernel option is specified. Not sure if my
> > > understanding is correct.
> 
>    Your understanding is almost correct. 
>    Only when "kernelcore=mirror" specified, the above procedure works.
>    But, if mirrored regions are existed, bootmem allocator tries to 
>    allocate from mirrored region independently of "kerenelcore=mirror" option.
> 
>    So, IMHO, kernel text is important, so putting it to mirrored (more reliable)
>    region is reasonable whether or not "kernelcore=mirror" is specified.

Ah, yeah, thanks for telling. So at boot time memblock will put mirror
region in highest priority to allocate. Then let me remove the
kernelcore=mirror handling code, the process_efi_entry will be simpler.

commit a3f5bafcc04aaf62990e0cf3ced1cc6d8dc6fe95
Author: Tony Luck <tony.luck@...el.com>
Date:   Wed Jun 24 16:58:12 2015 -0700

    mm/memblock: allocate boot time data structures from mirrored memory

> 
>    Anyway thanks for submitting patch.
>    We have Address Range Mirroring capable machine, so we'll test your patch.

Thanks a lot for help, Yasuaki Ishimatsu said he also will loan me a testing
machine when it's available.

Thanks
Baoquan

> > 
> > >
> > > NOTE:
> > > I haven't got a machine with efi mirror region enabled, so only test
> > > the
> > > e820 map processing case and the case of no mirror region on efi machine.
> > > So set this as a RFC patchset, will post formal one after above
> > > question is made clear and mirror issue test passed.
> > >
> > > Baoquan He (2):
> > >   x86/boot/KASLR: Adapt process_e820_entry for all kinds of memory map
> > >   x86/boot/KASLR: Restrict kernel to be randomized in mirror regions if
> > >     existed
> > >
> > >  arch/x86/boot/compressed/kaslr.c | 129
> > > +++++++++++++++++++++++++++++++--------
> > >  1 file changed, 104 insertions(+), 25 deletions(-)
> > >
> > > --
> > > 2.5.5
> > >
>