From 1a01d9772588523daedad9d783b033ed3d025552 Mon Sep 17 00:00:00 2001
From: Will Deacon <will.deacon@arm.com>
Date: Tue, 14 Nov 2017 14:41:01 +0000
Subject: [PATCH 49/51] arm64: Kconfig: Add CONFIG_UNMAP_KERNEL_AT_EL0

Git-commit: 084eb77cd3a81134d02500977dc0ecc9277dc97d
Patch-mainline: v4.16-rc1
References: bsc#1068032

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>
Signed-off-by: Mian Yousaf Kaukab <yousaf.kaukab@suse.com>
---
 arch/arm64/Kconfig | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 0b2ecb24fa80..a1b73d422726 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -778,6 +778,19 @@ 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.
 
+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
 	bool "Emulate deprecated/obsolete ARMv8 instructions"
 	depends on COMPAT
-- 
2.11.0