linux-kernel - [PATCH v2 25/34] compiler: Let data_race() imply disabled capability analysis

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Message-ID: <20250304092417.2873893-26-elver@google.com>
Date: Tue,  4 Mar 2025 10:21:24 +0100
From: Marco Elver <elver@...gle.com>
To: elver@...gle.com
Cc: "David S. Miller" <davem@...emloft.net>, Luc Van Oostenryck <luc.vanoostenryck@...il.com>, 
	"Paul E. McKenney" <paulmck@...nel.org>, Alexander Potapenko <glider@...gle.com>, Arnd Bergmann <arnd@...db.de>, 
	Bart Van Assche <bvanassche@....org>, Bill Wendling <morbo@...gle.com>, Boqun Feng <boqun.feng@...il.com>, 
	Dmitry Vyukov <dvyukov@...gle.com>, Eric Dumazet <edumazet@...gle.com>, 
	Frederic Weisbecker <frederic@...nel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Herbert Xu <herbert@...dor.apana.org.au>, Ingo Molnar <mingo@...nel.org>, 
	Jann Horn <jannh@...gle.com>, Jiri Slaby <jirislaby@...nel.org>, 
	Joel Fernandes <joel@...lfernandes.org>, Jonathan Corbet <corbet@....net>, 
	Josh Triplett <josh@...htriplett.org>, Justin Stitt <justinstitt@...gle.com>, 
	Kees Cook <kees@...nel.org>, Kentaro Takeda <takedakn@...data.co.jp>, 
	Mark Rutland <mark.rutland@....com>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, 
	Miguel Ojeda <ojeda@...nel.org>, Nathan Chancellor <nathan@...nel.org>, 
	Neeraj Upadhyay <neeraj.upadhyay@...nel.org>, Peter Zijlstra <peterz@...radead.org>, 
	Steven Rostedt <rostedt@...dmis.org>, Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>, 
	Thomas Gleixner <tglx@...utronix.de>, Uladzislau Rezki <urezki@...il.com>, Waiman Long <longman@...hat.com>, 
	Will Deacon <will@...nel.org>, kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org, 
	llvm@...ts.linux.dev, rcu@...r.kernel.org, linux-crypto@...r.kernel.org, 
	linux-serial@...r.kernel.org
Subject: [PATCH v2 25/34] compiler: Let data_race() imply disabled capability analysis

Many patterns that involve data-racy accesses often deliberately ignore
normal synchronization rules to avoid taking a lock.

If we have a lock-guarded variable on which we do a lock-less data-racy
access, rather than having to write capability_unsafe(data_race(..)),
simply make the data_race(..) macro imply capability-unsafety. The
data_race() macro already denotes the intent that something subtly
unsafe is about to happen, so it should be clear enough as-is.

Signed-off-by: Marco Elver <elver@...gle.com>
---
v2:
* New patch.
---
 include/linux/compiler.h       | 2 ++
 lib/test_capability-analysis.c | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 155385754824..c837464369df 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -186,7 +186,9 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
 #define data_race(expr)							\
 ({									\
 	__kcsan_disable_current();					\
+	disable_capability_analysis();					\
 	__auto_type __v = (expr);					\
+	enable_capability_analysis();					\
 	__kcsan_enable_current();					\
 	__v;								\
 })
diff --git a/lib/test_capability-analysis.c b/lib/test_capability-analysis.c
index 853fdc53840f..13e7732c38a2 100644
--- a/lib/test_capability-analysis.c
+++ b/lib/test_capability-analysis.c
@@ -92,6 +92,8 @@ static void __used test_raw_spinlock_trylock_extra(struct test_raw_spinlock_data
 {
 	unsigned long flags;
 
+	data_race(d->counter++); /* no warning */
+
 	if (raw_spin_trylock_irq(&d->lock)) {
 		d->counter++;
 		raw_spin_unlock_irq(&d->lock);
-- 
2.48.1.711.g2feabab25a-goog