[PATCH 5.19 0149/1157] arm64: kasan: do not instrument stacktrace.c

Greg Kroah-Hartman
2022-08-15T22:38:06Z

From: Andrey Konovalov <andreyknvl@google.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@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Link: https://lore.kernel.org/r/c4c944a2a905e949760fbeb29258185087171708.1653317461.git.andreyknvl@google.com
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.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