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Bug report about KASLR and ZONE_MOVABLE




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
'movablecore='.
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
0x0000000000001000-0x00000001f57fffff]

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.

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

Thanks,
Chao Fan