Currently kaslr only randomize physical address of kernel loading, then add the
delta
to virtual address of kernel text mapping. Because kernel virtual address can
only be
from __START_KERNEL_map to LOAD_PHYSICAL_ADDR+CONFIG_RANDOMIZE_BASE_MAX_OFFSET,
namely
[0xffffffff80000000, 0xffffffffc0000000], so physical address can only be
randomized
in region [LOAD_PHYSICAL_ADDR, CONFIG_RANDOMIZE_BASE_MAX_OFFSET], namely [16M,
1G].
So hpa and Vivek suggested the randomization should be done separately for both
physical
and virtual address. In this patchset I tried it. And after randomization,
relocation
handling only depends on virtual address changing, means I only check whether
virtual
address is randomized to other position, if yes relocation need be handled, if
no just
skip the relocation handling though physical address is randomized to different
place.
Now physical address can be randomized from 16M to 4G, virtual address offset
can be
from 16M to 1G.
Leftover problem:
hpa want to see the physical randomization can cover the whole physical
memory. I
checked code and found it's hard to do. Because in
arch/x86/boot/compressed/head_64.S
an identity mapping of 4G is built and then kaslr and decompressing are done.
The #PF
handler solution which he suggested is only available after jump into
decompressed
kernel, namely in arch/x86/kernel/head_64.S. I didn't think of a way to do the
whole
memory covering for physical address randomization, any suggestion or idea?
Baoquan He (6):
remove a unused function parameter
a bug that relocation can not be handled when kernel is loaded above
2G
Introduce a function to randomize the kernel text mapping address
adapt choose_kernel_location to add the kernel virtual address
randomzation
change the relocations behavior for kaslr on x86_64
extend the upper limit of kernel physical address randomization to 4G
arch/x86/boot/compressed/aslr.c | 69 ++++++++++++++++++++++++++++-------------
arch/x86/boot/compressed/misc.c | 34 +++++++++++++-------
arch/x86/boot/compressed/misc.h | 20 ++++++------
3 files changed, 82 insertions(+), 41 deletions(-)
--
1.9.3
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