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 16:03:29 +0800
From:   Baoquan He <bhe@...hat.com>
To:     linux-kernel@...r.kernel.org, izumi.taku@...fujitsu.com
Cc:     keescook@...omium.org, x86@...nel.org, fanc.fnst@...fujitsu.com,
        caoj.fnst@...fujitsu.com, douly.fnst@...fujitsu.com
Subject: Re: [RFC][PATCH 0/2] x86/boot/KASLR: Restrict kernel to be
 randomized in mirror regions if existed

Sorry, forget adding Taku to the list.

Hi Taku,

On 06/15/17 at 03:52pm, Baoquan He wrote:
> 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.
> 
> The functions of address range mirroring feature are as follows.
> - The physical memory region whose descriptors in EFI memory map have
>   EFI_MEMORY_MORE_RELIABLE attribute (bit: 16) are mirrored
> - The function arranges such mirror region into normal zone and other region
>   into movable zone in order to locate kernel code and data on mirror region
> 
> So we need restrict kernel to be located inside mirror region if it
> is existed.
> 
> 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.

Since you are the author of kernelcore=mirror related code and expert on
mirror feature, could you help answer above question?

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
>