[PATCH v3 17/20] arm64: Kconfig: Add CONFIG_UNMAP_KERNEL_AT_EL0
- Date: Wed, 6 Dec 2017 12:35:36 +0000
- From: Will Deacon <will.deacon@xxxxxxx>
- Subject: [PATCH v3 17/20] arm64: Kconfig: Add CONFIG_UNMAP_KERNEL_AT_EL0
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@xxxxxxx>
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
arch/arm64/Kconfig | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index fdcc7b9bb15d..3af1657fcac3 100644
@@ -833,6 +833,19 @@ config FORCE_MAX_ZONEORDER
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.
+ bool "Unmap kernel when running in userspace (aka \"KAISER\")"
+ default y
+ 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.
bool "Emulate deprecated/obsolete ARMv8 instructions"
depends on COMPAT