From mboxrd@z Thu Jan 1 00:00:00 1970 From: alex.shi@linaro.org (Alex Shi) Date: Wed, 28 Feb 2018 11:56:39 +0800 Subject: [PATCH 17/29] arm64: Kconfig: Add CONFIG_UNMAP_KERNEL_AT_EL0 In-Reply-To: <1519790211-16582-1-git-send-email-alex.shi@linaro.org> References: <1519790211-16582-1-git-send-email-alex.shi@linaro.org> Message-ID: <1519790211-16582-18-git-send-email-alex.shi@linaro.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org From: Will Deacon commit 084eb77cd3a8 upstream. 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. Reviewed-by: Mark Rutland Tested-by: Laura Abbott Tested-by: Shanker Donthineni Signed-off-by: Will Deacon Signed-off-by: Alex Shi --- arch/arm64/Kconfig | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 7769c2e..6b6e9f8 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -733,6 +733,19 @@ 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 -- 2.7.4