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Re: Bug report about KASLR and ZONE_MOVABLE

On Wed, Jul 11, 2018 at 05:42:44PM +0800, Chao Fan wrote:
>Hi all,
>I found there is a BUG about KASLR and ZONE_MOVABLE.
>When users use 'kernelcore=' parameter without 'movable_node',
>movable memory is evenly distributed to all nodes. The size of
>ZONE_MOVABLE depends on the kernel parameter 'kernelcore=' and
>But sometiomes, KASLR may put the uncompressed kernel to the
>tail position of a node, which will cause the kernel memory
>set as ZONE_MOVABLE. This region can not be offlined.
>Here is a very simple test in my qemu-kvm machine, there is
>only one node:
>The command line:
>[root@localhost ~]# cat /proc/cmdline
>BOOT_IMAGE=/vmlinuz-4.18.0-rc3+ root=/dev/mapper/fedora_localhost--live-root
>ro resume=/dev/mapper/fedora_localhost--live-swap
>rd.lvm.lv=fedora_localhost-live/root rd.lvm.lv=fedora_localhost-live/swap
>console=ttyS0 earlyprintk=ttyS0,115200n8 memblock=debug kernelcore=50%
>I use 'kernelcore=50%' here.
>Here is my early print result, I print the random_addr after KASLR chooses
>physical memory:
>early console in extract_kernel
>input_data: 0x000000000266b3b1
>input_len: 0x00000000007d8802
>output: 0x0000000001000000
>output_len: 0x0000000001e15698
>kernel_total_size: 0x0000000001a8b000
>trampoline_32bit: 0x000000000009d000
>booted via startup_32()
>Physical KASLR using RDRAND RDTSC...
>random_addr: 0x000000012f000000
>Virtual KASLR using RDRAND RDTSC...
>The address for kernel is 0x000000012f000000
>Here is the log of ZONE:
>[    0.000000] Zone ranges:
>[    0.000000]   DMA      [mem 0x0000000000001000-0x0000000000ffffff]
>[    0.000000]   DMA32    [mem 0x0000000001000000-0x00000000ffffffff]
>[    0.000000]   Normal   [mem 0x0000000100000000-0x00000001f57fffff]
>[    0.000000]   Device   empty
>[    0.000000] Movable zone start for each node
>[    0.000000]   Node 0: 0x000000011b000000
>[    0.000000] Early memory node ranges
>[    0.000000]   node   0: [mem 0x0000000000001000-0x000000000009efff]
>[    0.000000]   node   0: [mem 0x0000000000100000-0x00000000bffd6fff]
>[    0.000000]   node   0: [mem 0x0000000100000000-0x00000001f57fffff]
>[    0.000000] Initmem setup node 0 [mem
>Only one node in my machine, ZONE_MOVABLE begins from 0x000000011b000000,
>which is lower than 0x000000012f000000.
>So KASLR put the kernel to the ZONE_MOVABLE.
>Try to solve this problem, I think there should be a new tactic in function
>find_zone_movable_pfns_for_nodes() of mm/page_alloc.c. If kernel is uncompressed
>in a tail position, then just set the memory after the kernel as ZONE_MOVABLE,
>at the same time, memory in other nodes will be set as ZONE_MOVABLE.

Sorry, mistake here. It should be:
"more memory in other nodes will be set as ZONE_MOVABLE".

Chao Fan

>If there is something wrong, pleas let me know. And any comments will be welcome.
>Chao Fan