kcsan: Use tracing-safe version of prandom (cd290ec2) · Commits · 戴 / test

kernel/kcsan/core.c

+29 −6

Original line number	Diff line number	Diff line
		@@ -100,6 +100,9 @@ static atomic_long_t watchpoints[CONFIG_KCSAN_NUM_WATCHPOINTS + NUM_SLOTS-1];
		*/
		static DEFINE_PER_CPU(long, kcsan_skip);

		/* For kcsan_prandom_u32_max(). */
		static DEFINE_PER_CPU(struct rnd_state, kcsan_rand_state);

		static __always_inline atomic_long_t *find_watchpoint(unsigned long addr,
		size_t size,
		bool expect_write,
		@@ -271,11 +274,28 @@ should_watch(const volatile void ptr, size_t size, int type, struct kcsan_ctx
		return true;
		}

		/*
		* Returns a pseudo-random number in interval [0, ep_ro). See prandom_u32_max()
		* for more details.
		*
		* The open-coded version here is using only safe primitives for all contexts
		* where we can have KCSAN instrumentation. In particular, we cannot use
		* prandom_u32() directly, as its tracepoint could cause recursion.
		*/
		static u32 kcsan_prandom_u32_max(u32 ep_ro)
		{
		struct rnd_state *state = &get_cpu_var(kcsan_rand_state);
		const u32 res = prandom_u32_state(state);

		put_cpu_var(kcsan_rand_state);
		return (u32)(((u64) res * ep_ro) >> 32);
		}

		static inline void reset_kcsan_skip(void)
		{
		long skip_count = kcsan_skip_watch -
		(IS_ENABLED(CONFIG_KCSAN_SKIP_WATCH_RANDOMIZE) ?
		prandom_u32_max(kcsan_skip_watch) :
		kcsan_prandom_u32_max(kcsan_skip_watch) :
		0);
		this_cpu_write(kcsan_skip, skip_count);
		}
		@@ -285,16 +305,18 @@ static __always_inline bool kcsan_is_enabled(void)
		return READ_ONCE(kcsan_enabled) && get_ctx()->disable_count == 0;
		}

		static inline unsigned int get_delay(int type)
		/* Introduce delay depending on context and configuration. */
		static void delay_access(int type)
		{
		unsigned int delay = in_task() ? kcsan_udelay_task : kcsan_udelay_interrupt;
		/* For certain access types, skew the random delay to be longer. */
		unsigned int skew_delay_order =
		(type & (KCSAN_ACCESS_COMPOUND \| KCSAN_ACCESS_ASSERT)) ? 1 : 0;

		return delay - (IS_ENABLED(CONFIG_KCSAN_DELAY_RANDOMIZE) ?
		prandom_u32_max(delay >> skew_delay_order) :
		0);
		delay -= IS_ENABLED(CONFIG_KCSAN_DELAY_RANDOMIZE) ?
		kcsan_prandom_u32_max(delay >> skew_delay_order) :
		0;
		udelay(delay);
		}

		void kcsan_save_irqtrace(struct task_struct *task)
		@@ -476,7 +498,7 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type)
		* Delay this thread, to increase probability of observing a racy
		* conflicting access.
		*/
		udelay(get_delay(type));
		delay_access(type);

		/*
		* Re-read value, and check if it is as expected; if not, we infer a
		@@ -620,6 +642,7 @@ void __init kcsan_init(void)
		BUG_ON(!in_task());

		kcsan_debugfs_init();
		prandom_seed_full_state(&kcsan_rand_state);

		/*
		* We are in the init task, and no other tasks should be running;

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