From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753481AbdK3Qkh (ORCPT ); Thu, 30 Nov 2017 11:40:37 -0500 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:57576 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753369AbdK3Qjr (ORCPT ); Thu, 30 Nov 2017 11:39:47 -0500 From: Will Deacon To: linux-arm-kernel@lists.infradead.org Cc: linux-kernel@vger.kernel.org, catalin.marinas@arm.com, mark.rutland@arm.com, ard.biesheuvel@linaro.org, sboyd@codeaurora.org, dave.hansen@linux.intel.com, keescook@chromium.org, msalter@redhat.com, labbott@redhat.com, tglx@linutronix.de, Will Deacon Subject: [PATCH v2 17/18] arm64: Kconfig: Add CONFIG_UNMAP_KERNEL_AT_EL0 Date: Thu, 30 Nov 2017 16:39:45 +0000 Message-Id: <1512059986-21325-18-git-send-email-will.deacon@arm.com> X-Mailer: git-send-email 2.1.4 In-Reply-To: <1512059986-21325-1-git-send-email-will.deacon@arm.com> References: <1512059986-21325-1-git-send-email-will.deacon@arm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Signed-off-by: Will Deacon --- arch/arm64/Kconfig | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index fdcc7b9bb15d..3af1657fcac3 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -833,6 +833,19 @@ 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 -- 2.1.4