UPSTREAM: arm64: Kconfig: Add CONFIG_UNMAP_KERNEL_AT_EL0
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>
(cherry picked from commit 084eb77cd3a81134d02500977dc0ecc9277dc97d)
Change-Id: I70a996e448fa17007a3b8564c794e53e3992d7bf
Signed-off-by: Todd Poynor <toddpoynor@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Git-commit: 16f712b456b11f40a9b6931b585aa22e11df5057
Git-repo: https://android.googlesource.com/kernel/common/
Signed-off-by: Channagoud Kadabi <ckadabi@codeaurora.org>
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 0848993..629fc9c 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -781,6 +781,19 @@
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