From: Catalin Marinas <catalin.marinas@arm.com>
Date: Fri, 1 Jul 2016 17:25:31 +0000 (+0100)
Subject: FROMLIST: arm64: Enable CONFIG_ARM64_SW_TTBR0_PAN
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=67cd3bda54dadba4f8892105adf9c2f3982bfa0a;p=GitHub%2Fexynos8895%2Fandroid_kernel_samsung_universal8895.git

FROMLIST: 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>

Change-Id: Id00a8ad4169d6eb6176c468d953436eb4ae887ae
(cherry picked from commit 6a2d7bad43474c48b68394d455b84a16b7d7dc3f)
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
---

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index bf24d67a1ff1..488fed2d5e5e 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -706,6 +706,14 @@ config SETEND_EMULATION
 	  If unsure, say Y
 endif
 
+config ARM64_SW_TTBR0_PAN
+	bool "Emulate Priviledged 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