From mboxrd@z Thu Jan 1 00:00:00 1970 From: will.deacon@arm.com (Will Deacon) Date: Fri, 17 Nov 2017 18:22:01 +0000 Subject: [PATCH 18/18] arm64: Kconfig: Add CONFIG_UNMAP_KERNEL_AT_EL0 In-Reply-To: <1510942921-12564-1-git-send-email-will.deacon@arm.com> References: <1510942921-12564-1-git-send-email-will.deacon@arm.com> Message-ID: <1510942921-12564-19-git-send-email-will.deacon@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.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 f0fcbfc2262e..f99ffb88843a 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -796,6 +796,19 @@ 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