Messages in this thread | | | From | Baoquan He <> | Subject | [PATCH 0/6] randomize kernel physical address and virtual address separately | Date | Wed, 21 Jan 2015 11:37:11 +0800 |
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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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