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Date: Fri, 28 Oct 2016 18:27:16 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: linux-arm-kernel@...ts.infradead.org
Cc: Will Deacon <will.deacon@....com>,
James Morse <james.morse@....com>,
Kees Cook <keescook@...omium.org>,
Mark Rutland <mark.rutland@....com>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
AKASHI Takahiro <takahiro.akashi@...aro.org>,
Sami Tolvanen <samitolvanen@...gle.com>,
kernel-hardening@...ts.openwall.com
Subject: [PATCH v4 8/8] 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@....com>
Cc: James Morse <james.morse@....com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Mark Rutland <mark.rutland@....com>
Signed-off-by: Catalin Marinas <catalin.marinas@....com>
---
arch/arm64/Kconfig | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 969ef880d234..6b9a8446fc43 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -790,6 +790,14 @@ 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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