The patch below does not apply to the 5.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From b8fdef311a0bd9223f10754f94fdcf1a594a3457 Mon Sep 17 00:00:00 2001

From: Mark Brown broonie@kernel.org Date: Tue, 31 Mar 2020 20:44:59 +0100 Subject: [PATCH] arm64: Always force a branch protection mode when the compiler has one

Compilers with branch protection support can be configured to enable it by default, it is likely that distributions will do this as part of deploying branch protection system wide. As well as the slight overhead from having some extra NOPs for unused branch protection features this can cause more serious problems when the kernel is providing pointer authentication to userspace but not built for pointer authentication itself. In that case our switching of keys for userspace can affect the kernel unexpectedly, causing pointer authentication instructions in the kernel to corrupt addresses.

To ensure that we get consistent and reliable behaviour always explicitly initialise the branch protection mode, ensuring that the kernel is built the same way regardless of the compiler defaults.

Fixes: 7503197562567 (arm64: add basic pointer authentication support) Reported-by: Szabolcs Nagy szabolcs.nagy@arm.com Signed-off-by: Mark Brown broonie@kernel.org Cc: stable@vger.kernel.org [catalin.marinas@arm.com: remove Kconfig option in favour of Makefile check] Signed-off-by: Catalin Marinas catalin.marinas@arm.com

diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile index f15f92ba53e6..85e4149cc5d5 100644 --- a/arch/arm64/Makefile +++ b/arch/arm64/Makefile @@ -65,6 +65,10 @@ stack_protector_prepare: prepare0 include/generated/asm-offsets.h)) endif

+# Ensure that if the compiler supports branch protection we default it +# off, this will be overridden if we are using branch protection. +branch-prot-flags-y += $(call cc-option,-mbranch-protection=none) + ifeq ($(CONFIG_ARM64_PTR_AUTH),y) branch-prot-flags-$(CONFIG_CC_HAS_SIGN_RETURN_ADDRESS) := -msign-return-address=all branch-prot-flags-$(CONFIG_CC_HAS_BRANCH_PROT_PAC_RET) := -mbranch-protection=pac-ret+leaf @@ -73,9 +77,10 @@ branch-prot-flags-$(CONFIG_CC_HAS_BRANCH_PROT_PAC_RET) := -mbranch-protection=pa # we pass it only to the assembler. This option is utilized only in case of non # integrated assemblers. branch-prot-flags-$(CONFIG_AS_HAS_PAC) += -Wa,-march=armv8.3-a -KBUILD_CFLAGS += $(branch-prot-flags-y) endif

+KBUILD_CFLAGS += $(branch-prot-flags-y) + ifeq ($(CONFIG_CPU_BIG_ENDIAN), y) KBUILD_CPPFLAGS += -mbig-endian CHECKFLAGS += -D__AARCH64EB__