linux-kernel - [PATCH AUTOSEL 5.4 1/2] ARM: 9434/1: cfi: Fix compilation corner case

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Message-ID: <20241120140833.1769807-1-sashal@kernel.org>
Date: Wed, 20 Nov 2024 09:08:28 -0500
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Linus Walleij <linus.walleij@...aro.org>,
	kernel test robot <lkp@...el.com>,
	Nathan Chancellor <nathan@...nel.org>,
	Russell King <rmk+kernel@...linux.org.uk>,
	Sasha Levin <sashal@...nel.org>,
	linux@...linux.org.uk,
	arnd@...db.de,
	samitolvanen@...gle.com,
	linux-arm-kernel@...ts.infradead.org,
	llvm@...ts.linux.dev
Subject: [PATCH AUTOSEL 5.4 1/2] ARM: 9434/1: cfi: Fix compilation corner case

From: Linus Walleij <linus.walleij@...aro.org>

[ Upstream commit 4aea16b7cfb76bd3361858ceee6893ef5c9b5570 ]

When enabling expert mode CONFIG_EXPERT and using that power
user mode to disable the branch prediction hardening
!CONFIG_HARDEN_BRANCH_PREDICTOR, the assembly linker
in CLANG notices that some assembly in proc-v7.S does
not have corresponding C call sites, i.e. the prototypes
in proc-v7-bugs.c are enclosed in ifdef
CONFIG_HARDEN_BRANCH_PREDICTOR so this assembly:

SYM_TYPED_FUNC_START(cpu_v7_smc_switch_mm)
SYM_TYPED_FUNC_START(cpu_v7_hvc_switch_mm)

Results in:

ld.lld: error: undefined symbol: __kcfi_typeid_cpu_v7_smc_switch_mm
>>> referenced by proc-v7.S:94 (.../arch/arm/mm/proc-v7.S:94)
>>> arch/arm/mm/proc-v7.o:(.text+0x108) in archive vmlinux.a

ld.lld: error: undefined symbol: __kcfi_typeid_cpu_v7_hvc_switch_mm
>>> referenced by proc-v7.S:105 (.../arch/arm/mm/proc-v7.S:105)
>>> arch/arm/mm/proc-v7.o:(.text+0x124) in archive vmlinux.a

Fix this by adding an additional requirement that
CONFIG_HARDEN_BRANCH_PREDICTOR has to be enabled to compile
these assembly calls.

Closes: https://lore.kernel.org/oe-kbuild-all/202411041456.ZsoEiD7T-lkp@intel.com/

Reported-by: kernel test robot <lkp@...el.com>
Reviewed-by: Nathan Chancellor <nathan@...nel.org>
Signed-off-by: Linus Walleij <linus.walleij@...aro.org>
Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/arm/mm/proc-v7.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/mm/proc-v7.S b/arch/arm/mm/proc-v7.S
index 48e0ef6f0dccf..aee85fd261f5d 100644
--- a/arch/arm/mm/proc-v7.S
+++ b/arch/arm/mm/proc-v7.S
@@ -91,7 +91,7 @@ ENTRY(cpu_v7_dcache_clean_area)
 	ret	lr
 ENDPROC(cpu_v7_dcache_clean_area)
 
-#ifdef CONFIG_ARM_PSCI
+#if defined(CONFIG_ARM_PSCI) && defined(CONFIG_HARDEN_BRANCH_PREDICTOR)
 	.arch_extension sec
 ENTRY(cpu_v7_smc_switch_mm)
 	stmfd	sp!, {r0 - r3}
-- 
2.43.0