linux-kernel - [PATCH 5.13 173/800] arm64: entry: dont instrument entry code with KCOV

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Date:   Mon, 12 Jul 2021 08:03:16 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Will Deacon <will@...nel.org>, Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.13 173/800] arm64: entry: dont instrument entry code with KCOV

From: Mark Rutland <mark.rutland@....com>

[ Upstream commit bf6fa2c0dda751863c3446aa64d733013bec4a19 ]

The code in entry-common.c runs at exception entry and return
boundaries, where portions of the kernel environment aren't available.
For example, RCU may not be watching, and lockdep state may be
out-of-sync with the hardware. Due to this, it is not sound to
instrument this code.

We generally avoid instrumentation by marking the entry functions as
`noinstr`, but currently this doesn't inhibit KCOV instrumentation.
Prevent this by disabling KCOV for the entire compilation unit.

Signed-off-by: Mark Rutland <mark.rutland@....com>
Acked-by: Catalin Marinas <catalin.marinas@....com>
Acked-by: Marc Zyngier <maz@...nel.org>
Cc: James Morse <james.morse@....com>
Cc: Will Deacon <will@...nel.org>
Link: https://lore.kernel.org/r/20210607094624.34689-20-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/arm64/kernel/Makefile | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index 6cc97730790e..787c3c83edd7 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -14,6 +14,11 @@ CFLAGS_REMOVE_return_address.o = $(CC_FLAGS_FTRACE)
 CFLAGS_REMOVE_syscall.o	 = -fstack-protector -fstack-protector-strong
 CFLAGS_syscall.o	+= -fno-stack-protector
 
+# It's not safe to invoke KCOV when portions of the kernel environment aren't
+# available or are out-of-sync with HW state. Since `noinstr` doesn't always
+# inhibit KCOV instrumentation, disable it for the entire compilation unit.
+KCOV_INSTRUMENT_entry.o := n
+
 # Object file lists.
 obj-y			:= debug-monitors.o entry.o irq.o fpsimd.o		\
 			   entry-common.o entry-fpsimd.o process.o ptrace.o	\
-- 
2.30.2