From 9fa6a588dedcc0c86bafad5511f4b6096d2e7a5c Mon Sep 17 00:00:00 2001
From: Catalin Marinas <catalin.marinas@arm.com>
Date: Fri, 1 Jul 2016 18:25:31 +0100
Subject: arm64: Enable CONFIG_ARM64_SW_TTBR0_PAN

This patch adds the Kconfig option to enable support for TTBR0 PAN
emulation. The option is default off because of a slight performance hit
when enabled, caused by the additional TTBR0_EL1 switching during user
access operations or exception entry/exit code.

Cc: Will Deacon <will.deacon@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
(cherry picked from commit ba42822af1c287f038aa550f3578c61c212a892e)
Signed-off-by: Alex Shi <alex.shi@linaro.org>

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 6c636b4..a520166 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -801,6 +801,14 @@ config SETEND_EMULATION
 	  If unsure, say Y
 endif
 
+config ARM64_SW_TTBR0_PAN
+	bool "Emulate Privileged Access Never using TTBR0_EL1 switching"
+	help
+	  Enabling this option prevents the kernel from accessing
+	  user-space memory directly by pointing TTBR0_EL1 to a reserved
+	  zeroed area and reserved ASID. The user access routines
+	  restore the valid TTBR0_EL1 temporarily.
+
 menu "ARMv8.1 architectural features"
 
 config ARM64_HW_AFDBM
-- 
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