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FAILED: patch "[PATCH] arm64: Always force a branch protection mode when the" failed to apply to 5.6-stable tree

PATCH [email protected] 4 participants 5 messages Apr 15, 2020 – Apr 16, 2020

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Stable branch arm64
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#0 lore raw

The patch below does not apply to the 5.6-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 <[email protected]>.

thanks,

greg k-h

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

From b8fdef311a0bd9223f10754f94fdcf1a594a3457 Mon Sep 17 00:00:00 2001
From: Mark Brown <[email protected]>
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 <[email protected]>
Signed-off-by Mark Brown <[email protected]>
Cc [email protected]
[[email protected]: remove Kconfig option in favour of Makefile check]
Signed-off-by Catalin Marinas <[email protected]>
arch/arm64/Makefile +6 -1
index f15f92ba53e6..85e4149cc5d5 100644
@@ -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__
maintainer
#1 lore raw
Quoted 31 lines · On Wed, Apr 15, 2020 at 01:23:24PM +0200, [email protected] wrote:

The patch below does not apply to the 5.6-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 <[email protected]>.

thanks,

greg k-h

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

From b8fdef311a0bd9223f10754f94fdcf1a594a3457 Mon Sep 17 00:00:00 2001
From: Mark Brown <[email protected]>
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.

Quoted 6 lines
Fixes 7503197562567 (arm64: add basic pointer authentication support)
Reported-by Szabolcs Nagy <[email protected]>
Signed-off-by Mark Brown <[email protected]>
Cc [email protected]
[[email protected]: remove Kconfig option in favour of Makefile check]
Signed-off-by Catalin Marinas <[email protected]>

I don't think that this is needed anywhere without 74afda4016a7 ("arm64:
compile the kernel with ptrauth return address signing")?

Signature · 2 lines
Thanks,
Sasha
maintainer
#2 lore raw
Quoted 38 lines · Sasha Levin
Quoted 30 lines · On Wed, Apr 15, 2020 at 01:23:24PM +0200, [email protected] wrote:

The patch below does not apply to the 5.6-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 <[email protected]>.

thanks,

greg k-h

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

From b8fdef311a0bd9223f10754f94fdcf1a594a3457 Mon Sep 17 00:00:00 2001
From: Mark Brown <[email protected]>
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.

Quoted 6 lines
Fixes 7503197562567 (arm64: add basic pointer authentication support)
Reported-by Szabolcs Nagy <[email protected]>
Signed-off-by Mark Brown <[email protected]>
Cc [email protected]
[[email protected]: remove Kconfig option in favour of Makefile check]
Signed-off-by Catalin Marinas <[email protected]>
Quoted 2 lines

I don't think that this is needed anywhere without 74afda4016a7 ("arm64:
compile the kernel with ptrauth return address signing")?

Good point. Mark, is the Fixes line above correct or it should have been the one Sasha mentions?

Signature · 1 line
Catalin
#3 lore raw
Quoted 7 lines · Catalin Marinas
Quoted 2 lines · Sasha Levin

I don't think that this is needed anywhere without 74afda4016a7 ("arm64:
compile the kernel with ptrauth return address signing")?

Good point. Mark, is the Fixes line above correct or it should have been the one Sasha mentions?

Yes, Sasha's is right.

#4 lore raw
Quoted 10 lines · Mark Brown
Quoted 7 lines · Catalin Marinas
Quoted 2 lines · Sasha Levin

I don't think that this is needed anywhere without 74afda4016a7 ("arm64:
compile the kernel with ptrauth return address signing")?

Good point. Mark, is the Fixes line above correct or it should have been the one Sasha mentions?

Yes, Sasha's is right.

Actually, no - we do need a version of the fix for older versions prior to the kernel having pointer auth support since the goal was to ensure that the kernel doesn't actually get built with pointer auth when we are doing it for userspace as that leaves us with half baked pointer auth in the code. The original fixes was right and we want a redone backport.