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Subject[PATCH 4.9 065/102] arm64: Kconfig: Add CONFIG_UNMAP_KERNEL_AT_EL0
4.9-stable review patch.  If anyone has any objections, please let me know.


From: Will Deacon <>

commit 084eb77cd3a8 upstream.

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 <>
Tested-by: Laura Abbott <>
Tested-by: Shanker Donthineni <>
Signed-off-by: Will Deacon <>
Signed-off-by: Alex Shi <> [v4.9 backport]
Signed-off-by: Mark Rutland <> [v4.9 backport]
Tested-by: Will Deacon <>
Tested-by: Greg Hackmann <>
Signed-off-by: Greg Kroah-Hartman <>
arch/arm64/Kconfig | 13 +++++++++++++
1 file changed, 13 insertions(+)

--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -733,6 +733,19 @@ 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
+ 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.
bool "Emulate deprecated/obsolete ARMv8 instructions"
depends on COMPAT

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