[PATCH 5.16 40/53] arm64: Do not include __READ_ONCE() block in assembly files

Greg Kroah-Hartman
2022-03-10T14:14:44Z

From: Nathan Chancellor <nathan@kernel.org>

commit 52c9f93a9c482251cb0d224faa602ba26d462be8 upstream.

When building arm64 defconfig + CONFIG_LTO_CLANG_{FULL,THIN}=y after
commit 558c303c9734 ("arm64: Mitigate spectre style branch history side
channels"), the following error occurs:

<instantiation>:4:2: error: invalid fixup for movz/movk instruction
mov w0, #ARM_SMCCC_ARCH_WORKAROUND_3
^

Marc figured out that moving "#include <linux/init.h>" in
include/linux/arm-smccc.h into a !__ASSEMBLY__ block resolves it. The
full include chain with CONFIG_LTO=y from include/linux/arm-smccc.h:

include/linux/init.h
include/linux/compiler.h
arch/arm64/include/asm/rwonce.h
arch/arm64/include/asm/alternative-macros.h
arch/arm64/include/asm/assembler.h

The asm/alternative-macros.h include in asm/rwonce.h only happens when
CONFIG_LTO is set, which ultimately casues asm/assembler.h to be
included before the definition of ARM_SMCCC_ARCH_WORKAROUND_3. As a
result, the preprocessor does not expand ARM_SMCCC_ARCH_WORKAROUND_3 in
__mitigate_spectre_bhb_fw, which results in the error above.

Avoid this problem by just avoiding the CONFIG_LTO=y __READ_ONCE() block
in asm/rwonce.h with assembly files, as nothing in that block is useful
to assembly files, which allows ARM_SMCCC_ARCH_WORKAROUND_3 to be
properly expanded with CONFIG_LTO=y builds.

Fixes: e35123d83ee3 ("arm64: lto: Strengthen READ_ONCE() to acquire when CONFIG_LTO=y")
Cc: <stable@vger.kernel.org> # 5.11.x
Link: https://lore.kernel.org/r/20220309155716.3988480-1-maz@kernel.org/
Reported-by: Marc Zyngier <maz@kernel.org>
Acked-by: James Morse <james.morse@arm.com>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20220309191633.2307110-1-nathan@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/arm64/include/asm/rwonce.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/arch/arm64/include/asm/rwonce.h
+++ b/arch/arm64/include/asm/rwonce.h
@@ -5,7 +5,7 @@
#ifndef __ASM_RWONCE_H
#define __ASM_RWONCE_H

-#ifdef CONFIG_LTO
+#if defined(CONFIG_LTO) && !defined(__ASSEMBLY__)

#include <linux/compiler_types.h>
#include <asm/alternative-macros.h>
@@ -66,7 +66,7 @@
})

#endif /* !BUILD_VDSO */
-#endif /* CONFIG_LTO */
+#endif /* CONFIG_LTO && !__ASSEMBLY__ */

#include <asm-generic/rwonce.h>