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

From: Chao Fan
Date: Wed Jun 21 2017 - 23:12:12 EST

Hi all,

After testing this issue for 100 times in total, I think this patchset
works well.

The size of physical memory in my test machine is 229G, the size of
mirror region is 26G. In the 100 times, 50 times are with this patchset,
50 times are without it.

Here is my test result:

|total times|in non-mirror|in mirror
before patch| 50 | 41 | 9
with patch | 50 | 0 | 50

Firstly, I add the earlyprintk to get efi map when walking the efi map.
Then get the range of mirror regions.
In kaslr.c, add the earlyprintk to get random_addr in function
choose_random_location, find_random_phys_addr. Then check if the address
in which is choosen to extract kernel is in mirror region.

If there are any problems, please let me know.

Chao Fan

On Thu, Jun 15, 2017 at 03:52:47PM +0800, 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.
>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(-)