From: Will Deacon Date: Tue, 14 Nov 2017 14:41:01 +0000 (+0000) Subject: arm64: Kconfig: Add CONFIG_UNMAP_KERNEL_AT_EL0 X-Git-Tag: v4.14.20~154 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=332e0288200f6afe070e2c126680130195cec3d9;p=platform%2Fkernel%2Flinux-rpi.git arm64: Kconfig: Add CONFIG_UNMAP_KERNEL_AT_EL0 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: Ard Biesheuvel Signed-off-by: Greg Kroah-Hartman --- diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 3cec78c..5063d10 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -806,6 +806,19 @@ 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