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 <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: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 332e0288200f6afe070e2c126680130195cec3d9)

CVE-2017-5753
CVE-2017-5715
CVE-2017-5754

Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>
Acked-by: Brad Figg <brad.figg@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 4a84debc136cb37bb94950f68d28e432b0f540eb..d0c728cc9c8723c72f7f68c3891f5f3acee12c1f 100644 (file)
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -824,6 +824,19 @@ 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