From aeeac10b88e73ef060b86eacf50135aff608d628 Mon Sep 17 00:00:00 2001
From: Will Deacon <will.deacon@arm.com>
Date: Tue, 14 Nov 2017 16:19:39 +0000
Subject: [PATCH 07/24] arm64: Kconfig: Reword UNMAP_KERNEL_AT_EL0 kconfig
entry
Git-commit: 0617052ddde355ee663b2f048e67dd381e5ebd6a
Patch-mainline: v4.16-rc1
References: bsc#1068032
Although CONFIG_UNMAP_KERNEL_AT_EL0 does make KASLR more robust, it's
actually more useful as a mitigation against speculation attacks that
can leak arbitrary kernel data to userspace through speculation.
Reword the Kconfig help message to reflect this, and make the option
depend on EXPERT so that it is on by default for the majority of users.
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Mian Yousaf Kaukab <yousaf.kaukab@suse.com>
---
arch/arm64/Kconfig | 13 ++++++-------
1 file changed, 6 insertions(+), 7 deletions(-)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index a1b73d422726..20a7802fd5fc 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -779,15 +779,14 @@ config FORCE_MAX_ZONEORDER
4M allocations matching the default size used by generic code.
config UNMAP_KERNEL_AT_EL0
- bool "Unmap kernel when running in userspace (aka \"KAISER\")"
+ bool "Unmap kernel when running in userspace (aka \"KAISER\")" if EXPERT
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.
+ Speculation attacks against some high-performance processors can
+ be used to bypass MMU permission checks and leak kernel data to
+ userspace. This can be defended against by unmapping the kernel
+ when running in userspace, mapping it back in on exception entry
+ via a trampoline page in the vector table.
If unsure, say Y.
--
2.11.0