From: Will Deacon will.deacon@arm.com
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 mark.rutland@arm.com Tested-by: Laura Abbott labbott@redhat.com Tested-by: Shanker Donthineni shankerd@codeaurora.org Signed-off-by: Will Deacon will.deacon@arm.com Signed-off-by: Alex Shi alex.shi@linaro.org [v4.9 backport] Signed-off-by: Mark Rutland mark.rutland@arm.com [v4.9 backport] --- arch/arm64/Kconfig | 13 +++++++++++++ 1 file changed, 13 insertions(+)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 7769c2e27788..6b6e9f89e40a 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