linux-kernel - [PATCH AUTOSEL 5.19 03/58] arm64: kasan: do not instrument stacktrace.c

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Date:   Sun,  7 Aug 2022 21:30:21 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Andrey Konovalov <andreyknvl@...gle.com>,
        Mark Rutland <mark.rutland@....com>,
        Will Deacon <will@...nel.org>, Sasha Levin <sashal@...nel.org>,
        catalin.marinas@....com, broonie@...nel.org, keescook@...omium.org,
        joey.gouly@....com, andreyknvl@...il.com, ardb@...nel.org,
        masahiroy@...nel.org, kaleshsingh@...gle.com,
        madvenka@...ux.microsoft.com, mhiramat@...nel.org, maz@...nel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: [PATCH AUTOSEL 5.19 03/58] arm64: kasan: do not instrument stacktrace.c

From: Andrey Konovalov <andreyknvl@...gle.com>

[ Upstream commit 802b91118d11227b527153849ea761b280691373 ]

Disable KASAN instrumentation of arch/arm64/kernel/stacktrace.c.

This speeds up Generic KASAN by 5-20%.

As a side-effect, KASAN is now unable to detect bugs in the stack trace
collection code. This is taken as an acceptable downside.

Also replace READ_ONCE_NOCHECK() with READ_ONCE() in stacktrace.c.
As the file is now not instrumented, there is no need to use the
NOCHECK version of READ_ONCE().

Suggested-by: Mark Rutland <mark.rutland@....com>
Acked-by: Mark Rutland <mark.rutland@....com>
Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
Link: https://lore.kernel.org/r/c4c944a2a905e949760fbeb29258185087171708.1653317461.git.andreyknvl@google.com
Signed-off-by: Will Deacon <will@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/arm64/kernel/Makefile     | 5 +++++
 arch/arm64/kernel/stacktrace.c | 4 ++--
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index fa7981d0d917..7075a9c6a4a6 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
 
+# When KASAN is enabled, a stack trace is recorded for every alloc/free, which
+# can significantly impact performance. Avoid instrumenting the stack trace
+# collection code to minimize this impact.
+KASAN_SANITIZE_stacktrace.o := n
+
 # 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.
diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index 0467cb79f080..c246e8d9f95b 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -124,8 +124,8 @@ static int notrace unwind_next(struct task_struct *tsk,
 	 * Record this frame record's values and location. The prev_fp and
 	 * prev_type are only meaningful to the next unwind_next() invocation.
 	 */
-	state->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp));
-	state->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8));
+	state->fp = READ_ONCE(*(unsigned long *)(fp));
+	state->pc = READ_ONCE(*(unsigned long *)(fp + 8));
 	state->prev_fp = fp;
 	state->prev_type = info.type;
 
-- 
2.35.1