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arm64: Kconfig: Add CONFIG_UNMAP_KERNEL_AT_EL0

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Add a Kconfig entry to control use of the entry trampoline, which allows
us to unmap the kernel whilst running in userspace and improve the
robustness of KASLR.

Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Laura Abbott <labbott@redhat.com>
Tested-by: Shanker Donthineni <shankerd@codeaurora.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
Will Deacon 2017-11-14 14:41:01 +00:00
parent ea1e3de85e
commit 084eb77cd3
1 changed files with 13 additions and 0 deletions
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arch/arm64/Kconfig
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@ -833,6 +833,19 @@ config FORCE_MAX_ZONEORDER
However for 4K, we choose a higher default value, 11 as opposed to 10, giving us However for 4K, we choose a higher default value, 11 as opposed to 10, giving us
4M allocations matching the default size used by generic code. 4M allocations matching the default size used by generic code.
config UNMAP_KERNEL_AT_EL0
bool "Unmap kernel when running in userspace (aka \"KAISER\")"
default y
help
Some attacks against KASLR make use of the timing difference between
a permission fault which could arise from a page table entry that is
present in the TLB, and a translation fault which always requires a
page table walk. This option defends against these attacks by unmapping
the kernel whilst running in userspace, therefore forcing translation
faults for all of kernel space.
If unsure, say Y.
menuconfig ARMV8_DEPRECATED menuconfig ARMV8_DEPRECATED
bool "Emulate deprecated/obsolete ARMv8 instructions" bool "Emulate deprecated/obsolete ARMv8 instructions"
depends on COMPAT depends on COMPAT