| From | Greg Kroah-Hartman <> | Subject | [PATCH 4.15 034/202] [Variant 3/Meltdown] arm64: Kconfig: Add CONFIG_UNMAP_KERNEL_AT_EL0 | Date | Thu, 15 Feb 2018 16:15:34 +0100 |
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4.15-stable review patch. If anyone has any objections, please let me know.
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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: Greg Kroah-Hartman <gregkh@linuxfoundation.org> --- arch/arm64/Kconfig | 13 +++++++++++++ 1 file changed, 13 insertions(+)
--- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -843,6 +843,19 @@ 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
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