// SPDX-License-Identifier: GPL-2.0

  #define pr_fmt(fmt) "kcsan: " fmt

  #include <linux/atomic.h>
  #include <linux/bug.h>
  #include <linux/delay.h>
  #include <linux/export.h>
  #include <linux/init.h>

  #include <linux/kernel.h>

  #include <linux/list.h>

  #include <linux/moduleparam.h>

  #include <linux/percpu.h>
  #include <linux/preempt.h>
  #include <linux/random.h>
  #include <linux/sched.h>
  #include <linux/uaccess.h>
  
  #include "atomic.h"
  #include "encoding.h"
  #include "kcsan.h"

  static bool kcsan_early_enable = IS_ENABLED(CONFIG_KCSAN_EARLY_ENABLE);

  unsigned int kcsan_udelay_task = CONFIG_KCSAN_UDELAY_TASK;
  unsigned int kcsan_udelay_interrupt = CONFIG_KCSAN_UDELAY_INTERRUPT;

  static long kcsan_skip_watch = CONFIG_KCSAN_SKIP_WATCH;

  static bool kcsan_interrupt_watcher = IS_ENABLED(CONFIG_KCSAN_INTERRUPT_WATCHER);

  
  #ifdef MODULE_PARAM_PREFIX
  #undef MODULE_PARAM_PREFIX
  #endif
  #define MODULE_PARAM_PREFIX "kcsan."
  module_param_named(early_enable, kcsan_early_enable, bool, 0);
  module_param_named(udelay_task, kcsan_udelay_task, uint, 0644);
  module_param_named(udelay_interrupt, kcsan_udelay_interrupt, uint, 0644);
  module_param_named(skip_watch, kcsan_skip_watch, long, 0644);

  module_param_named(interrupt_watcher, kcsan_interrupt_watcher, bool, 0444);

  bool kcsan_enabled;
  
  /* Per-CPU kcsan_ctx for interrupts */
  static DEFINE_PER_CPU(struct kcsan_ctx, kcsan_cpu_ctx) = {

  	.disable_count		= 0,
  	.atomic_next		= 0,
  	.atomic_nest_count	= 0,
  	.in_flat_atomic		= false,

  	.access_mask		= 0,

  	.scoped_accesses	= {LIST_POISON1, NULL},

  };
  
  /*

   * Helper macros to index into adjacent slots, starting from address slot

   * itself, followed by the right and left slots.
   *
   * The purpose is 2-fold:
   *
   *	1. if during insertion the address slot is already occupied, check if
   *	   any adjacent slots are free;
   *	2. accesses that straddle a slot boundary due to size that exceeds a
   *	   slot's range may check adjacent slots if any watchpoint matches.
   *
   * Note that accesses with very large size may still miss a watchpoint; however,
   * given this should be rare, this is a reasonable trade-off to make, since this
   * will avoid:
   *
   *	1. excessive contention between watchpoint checks and setup;
   *	2. larger number of simultaneous watchpoints without sacrificing
   *	   performance.
   *
   * Example: SLOT_IDX values for KCSAN_CHECK_ADJACENT=1, where i is [0, 1, 2]:
   *
   *   slot=0:  [ 1,  2,  0]
   *   slot=9:  [10, 11,  9]
   *   slot=63: [64, 65, 63]
   */

  #define SLOT_IDX(slot, i) (slot + ((i + KCSAN_CHECK_ADJACENT) % NUM_SLOTS))
  
  /*

   * SLOT_IDX_FAST is used in the fast-path. Not first checking the address's primary

   * slot (middle) is fine if we assume that races occur rarely. The set of

   * indices {SLOT_IDX(slot, i) | i in [0, NUM_SLOTS)} is equivalent to
   * {SLOT_IDX_FAST(slot, i) | i in [0, NUM_SLOTS)}.
   */
  #define SLOT_IDX_FAST(slot, i) (slot + i)
  
  /*
   * Watchpoints, with each entry encoded as defined in encoding.h: in order to be
   * able to safely update and access a watchpoint without introducing locking
   * overhead, we encode each watchpoint as a single atomic long. The initial
   * zero-initialized state matches INVALID_WATCHPOINT.
   *
   * Add NUM_SLOTS-1 entries to account for overflow; this helps avoid having to

   * use more complicated SLOT_IDX_FAST calculation with modulo in the fast-path.

   */

  static atomic_long_t watchpoints[CONFIG_KCSAN_NUM_WATCHPOINTS + NUM_SLOTS-1];

  
  /*
   * Instructions to skip watching counter, used in should_watch(). We use a
   * per-CPU counter to avoid excessive contention.
   */
  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,
  						      long *encoded_watchpoint)

  {
  	const int slot = watchpoint_slot(addr);
  	const unsigned long addr_masked = addr & WATCHPOINT_ADDR_MASK;
  	atomic_long_t *watchpoint;
  	unsigned long wp_addr_masked;
  	size_t wp_size;
  	bool is_write;
  	int i;
  
  	BUILD_BUG_ON(CONFIG_KCSAN_NUM_WATCHPOINTS < NUM_SLOTS);
  
  	for (i = 0; i < NUM_SLOTS; ++i) {
  		watchpoint = &watchpoints[SLOT_IDX_FAST(slot, i)];
  		*encoded_watchpoint = atomic_long_read(watchpoint);
  		if (!decode_watchpoint(*encoded_watchpoint, &wp_addr_masked,
  				       &wp_size, &is_write))
  			continue;
  
  		if (expect_write && !is_write)
  			continue;
  
  		/* Check if the watchpoint matches the access. */
  		if (matching_access(wp_addr_masked, wp_size, addr_masked, size))
  			return watchpoint;
  	}
  
  	return NULL;
  }

  static inline atomic_long_t *
  insert_watchpoint(unsigned long addr, size_t size, bool is_write)

  {
  	const int slot = watchpoint_slot(addr);
  	const long encoded_watchpoint = encode_watchpoint(addr, size, is_write);
  	atomic_long_t *watchpoint;
  	int i;
  
  	/* Check slot index logic, ensuring we stay within array bounds. */
  	BUILD_BUG_ON(SLOT_IDX(0, 0) != KCSAN_CHECK_ADJACENT);

  	BUILD_BUG_ON(SLOT_IDX(0, KCSAN_CHECK_ADJACENT+1) != 0);
  	BUILD_BUG_ON(SLOT_IDX(CONFIG_KCSAN_NUM_WATCHPOINTS-1, KCSAN_CHECK_ADJACENT) != ARRAY_SIZE(watchpoints)-1);
  	BUILD_BUG_ON(SLOT_IDX(CONFIG_KCSAN_NUM_WATCHPOINTS-1, KCSAN_CHECK_ADJACENT+1) != ARRAY_SIZE(watchpoints) - NUM_SLOTS);

  
  	for (i = 0; i < NUM_SLOTS; ++i) {
  		long expect_val = INVALID_WATCHPOINT;
  
  		/* Try to acquire this slot. */
  		watchpoint = &watchpoints[SLOT_IDX(slot, i)];

  		if (atomic_long_try_cmpxchg_relaxed(watchpoint, &expect_val, encoded_watchpoint))

  			return watchpoint;
  	}
  
  	return NULL;
  }
  
  /*
   * Return true if watchpoint was successfully consumed, false otherwise.
   *
   * This may return false if:
   *
   *	1. another thread already consumed the watchpoint;
   *	2. the thread that set up the watchpoint already removed it;
   *	3. the watchpoint was removed and then re-used.
   */

  static __always_inline bool

  try_consume_watchpoint(atomic_long_t *watchpoint, long encoded_watchpoint)

  {

  	return atomic_long_try_cmpxchg_relaxed(watchpoint, &encoded_watchpoint, CONSUMED_WATCHPOINT);

  }

  /* Return true if watchpoint was not touched, false if already consumed. */
  static inline bool consume_watchpoint(atomic_long_t *watchpoint)

  {

  	return atomic_long_xchg_relaxed(watchpoint, CONSUMED_WATCHPOINT) != CONSUMED_WATCHPOINT;
  }
  
  /* Remove the watchpoint -- its slot may be reused after. */
  static inline void remove_watchpoint(atomic_long_t *watchpoint)
  {
  	atomic_long_set(watchpoint, INVALID_WATCHPOINT);

  }

  static __always_inline struct kcsan_ctx *get_ctx(void)

  {
  	/*

  	 * In interrupts, use raw_cpu_ptr to avoid unnecessary checks, that would

  	 * also result in calls that generate warnings in uaccess regions.
  	 */
  	return in_task() ? &current->kcsan_ctx : raw_cpu_ptr(&kcsan_cpu_ctx);
  }

  /* Check scoped accesses; never inline because this is a slow-path! */
  static noinline void kcsan_check_scoped_accesses(void)
  {
  	struct kcsan_ctx *ctx = get_ctx();
  	struct list_head *prev_save = ctx->scoped_accesses.prev;
  	struct kcsan_scoped_access *scoped_access;
  
  	ctx->scoped_accesses.prev = NULL;  /* Avoid recursion. */
  	list_for_each_entry(scoped_access, &ctx->scoped_accesses, list)
  		__kcsan_check_access(scoped_access->ptr, scoped_access->size, scoped_access->type);
  	ctx->scoped_accesses.prev = prev_save;
  }

  /* Rules for generic atomic accesses. Called from fast-path. */

  static __always_inline bool

  is_atomic(const volatile void *ptr, size_t size, int type, struct kcsan_ctx *ctx)

  {

  	if (type & KCSAN_ACCESS_ATOMIC)

  		return true;

  	/*
  	 * Unless explicitly declared atomic, never consider an assertion access
  	 * as atomic. This allows using them also in atomic regions, such as
  	 * seqlocks, without implicitly changing their semantics.
  	 */

  	if (type & KCSAN_ACCESS_ASSERT)

  		return false;

  	if (IS_ENABLED(CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC) &&

  	    (type & KCSAN_ACCESS_WRITE) && size <= sizeof(long) &&

  	    !(type & KCSAN_ACCESS_COMPOUND) && IS_ALIGNED((unsigned long)ptr, size))

  		return true; /* Assume aligned writes up to word size are atomic. */

  	if (ctx->atomic_next > 0) {

  		/*
  		 * Because we do not have separate contexts for nested
  		 * interrupts, in case atomic_next is set, we simply assume that
  		 * the outer interrupt set atomic_next. In the worst case, we
  		 * will conservatively consider operations as atomic. This is a
  		 * reasonable trade-off to make, since this case should be
  		 * extremely rare; however, even if extremely rare, it could
  		 * lead to false positives otherwise.
  		 */
  		if ((hardirq_count() >> HARDIRQ_SHIFT) < 2)
  			--ctx->atomic_next; /* in task, or outer interrupt */
  		return true;
  	}

  	return ctx->atomic_nest_count > 0 || ctx->in_flat_atomic;

  }

  static __always_inline bool

  should_watch(const volatile void *ptr, size_t size, int type, struct kcsan_ctx *ctx)

  {
  	/*
  	 * Never set up watchpoints when memory operations are atomic.
  	 *
  	 * Need to check this first, before kcsan_skip check below: (1) atomics
  	 * should not count towards skipped instructions, and (2) to actually
  	 * decrement kcsan_atomic_next for consecutive instruction stream.
  	 */

  	if (is_atomic(ptr, size, type, ctx))

  		return false;
  
  	if (this_cpu_dec_return(kcsan_skip) >= 0)
  		return false;
  
  	/*
  	 * NOTE: If we get here, kcsan_skip must always be reset in slow path
  	 * via reset_kcsan_skip() to avoid underflow.
  	 */
  
  	/* this operation should be watched */
  	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) ?

  				   kcsan_prandom_u32_max(kcsan_skip_watch) :

  				   0);
  	this_cpu_write(kcsan_skip, skip_count);
  }

  static __always_inline bool kcsan_is_enabled(void)

  {
  	return READ_ONCE(kcsan_enabled) && get_ctx()->disable_count == 0;
  }

  /* 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;

  	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)
  {
  #ifdef CONFIG_TRACE_IRQFLAGS
  	task->kcsan_save_irqtrace = task->irqtrace;
  #endif
  }
  
  void kcsan_restore_irqtrace(struct task_struct *task)
  {
  #ifdef CONFIG_TRACE_IRQFLAGS
  	task->irqtrace = task->kcsan_save_irqtrace;
  #endif
  }

  /*
   * Pull everything together: check_access() below contains the performance
   * critical operations; the fast-path (including check_access) functions should
   * all be inlinable by the instrumentation functions.
   *
   * The slow-path (kcsan_found_watchpoint, kcsan_setup_watchpoint) are
   * non-inlinable -- note that, we prefix these with "kcsan_" to ensure they can
   * be filtered from the stacktrace, as well as give them unique names for the
   * UACCESS whitelist of objtool. Each function uses user_access_save/restore(),
   * since they do not access any user memory, but instrumentation is still
   * emitted in UACCESS regions.
   */
  
  static noinline void kcsan_found_watchpoint(const volatile void *ptr,

  					    size_t size,

  					    int type,

  					    atomic_long_t *watchpoint,
  					    long encoded_watchpoint)
  {
  	unsigned long flags;
  	bool consumed;
  
  	if (!kcsan_is_enabled())
  		return;

  
  	/*
  	 * The access_mask check relies on value-change comparison. To avoid
  	 * reporting a race where e.g. the writer set up the watchpoint, but the
  	 * reader has access_mask!=0, we have to ignore the found watchpoint.
  	 */
  	if (get_ctx()->access_mask != 0)
  		return;

  	/*
  	 * Consume the watchpoint as soon as possible, to minimize the chances
  	 * of !consumed. Consuming the watchpoint must always be guarded by
  	 * kcsan_is_enabled() check, as otherwise we might erroneously
  	 * triggering reports when disabled.
  	 */
  	consumed = try_consume_watchpoint(watchpoint, encoded_watchpoint);
  
  	/* keep this after try_consume_watchpoint */
  	flags = user_access_save();
  
  	if (consumed) {

  		kcsan_save_irqtrace(current);

  		kcsan_report(ptr, size, type, KCSAN_VALUE_CHANGE_MAYBE,

  			     KCSAN_REPORT_CONSUMED_WATCHPOINT,
  			     watchpoint - watchpoints);

  		kcsan_restore_irqtrace(current);

  	} else {
  		/*
  		 * The other thread may not print any diagnostics, as it has
  		 * already removed the watchpoint, or another thread consumed
  		 * the watchpoint before this thread.
  		 */

  		atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_REPORT_RACES]);

  	}

  
  	if ((type & KCSAN_ACCESS_ASSERT) != 0)

  		atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_ASSERT_FAILURES]);

  	else

  		atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_DATA_RACES]);

  
  	user_access_restore(flags);
  }

  static noinline void

  kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type)

  {

  	const bool is_write = (type & KCSAN_ACCESS_WRITE) != 0;

  	const bool is_assert = (type & KCSAN_ACCESS_ASSERT) != 0;

  	atomic_long_t *watchpoint;
  	union {
  		u8 _1;
  		u16 _2;
  		u32 _4;
  		u64 _8;
  	} expect_value;

  	unsigned long access_mask;

  	enum kcsan_value_change value_change = KCSAN_VALUE_CHANGE_MAYBE;

  	unsigned long ua_flags = user_access_save();

  	unsigned long irq_flags = 0;

  
  	/*
  	 * Always reset kcsan_skip counter in slow-path to avoid underflow; see
  	 * should_watch().
  	 */
  	reset_kcsan_skip();
  
  	if (!kcsan_is_enabled())
  		goto out;

  	/*
  	 * Special atomic rules: unlikely to be true, so we check them here in
  	 * the slow-path, and not in the fast-path in is_atomic(). Call after
  	 * kcsan_is_enabled(), as we may access memory that is not yet
  	 * initialized during early boot.
  	 */
  	if (!is_assert && kcsan_is_atomic_special(ptr))
  		goto out;

  	if (!check_encodable((unsigned long)ptr, size)) {

  		atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_UNENCODABLE_ACCESSES]);

  		goto out;
  	}

  	/*
  	 * Save and restore the IRQ state trace touched by KCSAN, since KCSAN's
  	 * runtime is entered for every memory access, and potentially useful
  	 * information is lost if dirtied by KCSAN.
  	 */
  	kcsan_save_irqtrace(current);

  	if (!kcsan_interrupt_watcher)

  		local_irq_save(irq_flags);

  
  	watchpoint = insert_watchpoint((unsigned long)ptr, size, is_write);
  	if (watchpoint == NULL) {
  		/*

  		 * Out of capacity: the size of 'watchpoints', and the frequency
  		 * with which should_watch() returns true should be tweaked so

  		 * that this case happens very rarely.
  		 */

  		atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_NO_CAPACITY]);

  		goto out_unlock;
  	}

  	atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_SETUP_WATCHPOINTS]);
  	atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_USED_WATCHPOINTS]);

  
  	/*
  	 * Read the current value, to later check and infer a race if the data
  	 * was modified via a non-instrumented access, e.g. from a device.
  	 */

  	expect_value._8 = 0;

  	switch (size) {
  	case 1:
  		expect_value._1 = READ_ONCE(*(const u8 *)ptr);
  		break;
  	case 2:
  		expect_value._2 = READ_ONCE(*(const u16 *)ptr);
  		break;
  	case 4:
  		expect_value._4 = READ_ONCE(*(const u32 *)ptr);
  		break;
  	case 8:
  		expect_value._8 = READ_ONCE(*(const u64 *)ptr);
  		break;
  	default:
  		break; /* ignore; we do not diff the values */
  	}
  
  	if (IS_ENABLED(CONFIG_KCSAN_DEBUG)) {
  		kcsan_disable_current();

  		pr_err("watching %s, size: %zu, addr: %px [slot: %d, encoded: %lx]
  ",

  		       is_write ? "write" : "read", size, ptr,
  		       watchpoint_slot((unsigned long)ptr),
  		       encode_watchpoint((unsigned long)ptr, size, is_write));
  		kcsan_enable_current();
  	}
  
  	/*
  	 * Delay this thread, to increase probability of observing a racy
  	 * conflicting access.
  	 */

  	delay_access(type);

  
  	/*
  	 * Re-read value, and check if it is as expected; if not, we infer a
  	 * racy access.
  	 */

  	access_mask = get_ctx()->access_mask;

  	switch (size) {
  	case 1:

  		expect_value._1 ^= READ_ONCE(*(const u8 *)ptr);

  		if (access_mask)
  			expect_value._1 &= (u8)access_mask;

  		break;
  	case 2:

  		expect_value._2 ^= READ_ONCE(*(const u16 *)ptr);

  		if (access_mask)
  			expect_value._2 &= (u16)access_mask;

  		break;
  	case 4:

  		expect_value._4 ^= READ_ONCE(*(const u32 *)ptr);

  		if (access_mask)
  			expect_value._4 &= (u32)access_mask;

  		break;
  	case 8:

  		expect_value._8 ^= READ_ONCE(*(const u64 *)ptr);

  		if (access_mask)
  			expect_value._8 &= (u64)access_mask;

  		break;
  	default:
  		break; /* ignore; we do not diff the values */
  	}

  	/* Were we able to observe a value-change? */
  	if (expect_value._8 != 0)
  		value_change = KCSAN_VALUE_CHANGE_TRUE;

  	/* Check if this access raced with another. */

  	if (!consume_watchpoint(watchpoint)) {

  		/*

  		 * Depending on the access type, map a value_change of MAYBE to

  		 * TRUE (always report) or FALSE (never report).

  		 */

  		if (value_change == KCSAN_VALUE_CHANGE_MAYBE) {
  			if (access_mask != 0) {
  				/*
  				 * For access with access_mask, we require a
  				 * value-change, as it is likely that races on
  				 * ~access_mask bits are expected.
  				 */
  				value_change = KCSAN_VALUE_CHANGE_FALSE;
  			} else if (size > 8 || is_assert) {
  				/* Always assume a value-change. */
  				value_change = KCSAN_VALUE_CHANGE_TRUE;
  			}

  		}
  
  		/*

  		 * No need to increment 'data_races' counter, as the racing
  		 * thread already did.

  		 *
  		 * Count 'assert_failures' for each failed ASSERT access,
  		 * therefore both this thread and the racing thread may
  		 * increment this counter.

  		 */

  		if (is_assert && value_change == KCSAN_VALUE_CHANGE_TRUE)

  			atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_ASSERT_FAILURES]);

  		kcsan_report(ptr, size, type, value_change, KCSAN_REPORT_RACE_SIGNAL,
  			     watchpoint - watchpoints);

  	} else if (value_change == KCSAN_VALUE_CHANGE_TRUE) {

  		/* Inferring a race, since the value should not have changed. */

  		atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_RACES_UNKNOWN_ORIGIN]);

  		if (is_assert)

  			atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_ASSERT_FAILURES]);

  
  		if (IS_ENABLED(CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN) || is_assert)

  			kcsan_report(ptr, size, type, KCSAN_VALUE_CHANGE_TRUE,

  				     KCSAN_REPORT_RACE_UNKNOWN_ORIGIN,
  				     watchpoint - watchpoints);

  	}

  	/*
  	 * Remove watchpoint; must be after reporting, since the slot may be
  	 * reused after this point.
  	 */
  	remove_watchpoint(watchpoint);

  	atomic_long_dec(&kcsan_counters[KCSAN_COUNTER_USED_WATCHPOINTS]);

  out_unlock:

  	if (!kcsan_interrupt_watcher)

  		local_irq_restore(irq_flags);

  	kcsan_restore_irqtrace(current);

  out:
  	user_access_restore(ua_flags);
  }
  
  static __always_inline void check_access(const volatile void *ptr, size_t size,
  					 int type)
  {
  	const bool is_write = (type & KCSAN_ACCESS_WRITE) != 0;
  	atomic_long_t *watchpoint;
  	long encoded_watchpoint;
  
  	/*

  	 * Do nothing for 0 sized check; this comparison will be optimized out
  	 * for constant sized instrumentation (__tsan_{read,write}N).
  	 */
  	if (unlikely(size == 0))
  		return;
  
  	/*

  	 * Avoid user_access_save in fast-path: find_watchpoint is safe without
  	 * user_access_save, as the address that ptr points to is only used to
  	 * check if a watchpoint exists; ptr is never dereferenced.
  	 */
  	watchpoint = find_watchpoint((unsigned long)ptr, size, !is_write,
  				     &encoded_watchpoint);
  	/*
  	 * It is safe to check kcsan_is_enabled() after find_watchpoint in the

  	 * slow-path, as long as no state changes that cause a race to be

  	 * detected and reported have occurred until kcsan_is_enabled() is
  	 * checked.
  	 */
  
  	if (unlikely(watchpoint != NULL))

  		kcsan_found_watchpoint(ptr, size, type, watchpoint,

  				       encoded_watchpoint);

  	else {
  		struct kcsan_ctx *ctx = get_ctx(); /* Call only once in fast-path. */
  
  		if (unlikely(should_watch(ptr, size, type, ctx)))
  			kcsan_setup_watchpoint(ptr, size, type);
  		else if (unlikely(ctx->scoped_accesses.prev))
  			kcsan_check_scoped_accesses();
  	}

  }
  
  /* === Public interface ===================================================== */
  
  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;
  	 * WRITE_ONCE without memory barrier is sufficient.
  	 */

  	if (kcsan_early_enable) {
  		pr_info("enabled early
  ");

  		WRITE_ONCE(kcsan_enabled, true);

  	}

  }
  
  /* === Exported interface =================================================== */
  
  void kcsan_disable_current(void)
  {
  	++get_ctx()->disable_count;
  }
  EXPORT_SYMBOL(kcsan_disable_current);
  
  void kcsan_enable_current(void)
  {
  	if (get_ctx()->disable_count-- == 0) {
  		/*
  		 * Warn if kcsan_enable_current() calls are unbalanced with
  		 * kcsan_disable_current() calls, which causes disable_count to
  		 * become negative and should not happen.
  		 */
  		kcsan_disable_current(); /* restore to 0, KCSAN still enabled */
  		kcsan_disable_current(); /* disable to generate warning */
  		WARN(1, "Unbalanced %s()", __func__);
  		kcsan_enable_current();
  	}
  }
  EXPORT_SYMBOL(kcsan_enable_current);

  void kcsan_enable_current_nowarn(void)
  {
  	if (get_ctx()->disable_count-- == 0)
  		kcsan_disable_current();
  }
  EXPORT_SYMBOL(kcsan_enable_current_nowarn);

  void kcsan_nestable_atomic_begin(void)
  {
  	/*
  	 * Do *not* check and warn if we are in a flat atomic region: nestable
  	 * and flat atomic regions are independent from each other.
  	 * See include/linux/kcsan.h: struct kcsan_ctx comments for more
  	 * comments.
  	 */
  
  	++get_ctx()->atomic_nest_count;
  }
  EXPORT_SYMBOL(kcsan_nestable_atomic_begin);
  
  void kcsan_nestable_atomic_end(void)
  {
  	if (get_ctx()->atomic_nest_count-- == 0) {
  		/*
  		 * Warn if kcsan_nestable_atomic_end() calls are unbalanced with
  		 * kcsan_nestable_atomic_begin() calls, which causes
  		 * atomic_nest_count to become negative and should not happen.
  		 */
  		kcsan_nestable_atomic_begin(); /* restore to 0 */
  		kcsan_disable_current(); /* disable to generate warning */
  		WARN(1, "Unbalanced %s()", __func__);
  		kcsan_enable_current();
  	}
  }
  EXPORT_SYMBOL(kcsan_nestable_atomic_end);
  
  void kcsan_flat_atomic_begin(void)
  {
  	get_ctx()->in_flat_atomic = true;
  }
  EXPORT_SYMBOL(kcsan_flat_atomic_begin);
  
  void kcsan_flat_atomic_end(void)
  {
  	get_ctx()->in_flat_atomic = false;
  }
  EXPORT_SYMBOL(kcsan_flat_atomic_end);
  
  void kcsan_atomic_next(int n)
  {
  	get_ctx()->atomic_next = n;
  }
  EXPORT_SYMBOL(kcsan_atomic_next);

  void kcsan_set_access_mask(unsigned long mask)
  {
  	get_ctx()->access_mask = mask;
  }
  EXPORT_SYMBOL(kcsan_set_access_mask);

  struct kcsan_scoped_access *
  kcsan_begin_scoped_access(const volatile void *ptr, size_t size, int type,
  			  struct kcsan_scoped_access *sa)
  {
  	struct kcsan_ctx *ctx = get_ctx();
  
  	__kcsan_check_access(ptr, size, type);
  
  	ctx->disable_count++; /* Disable KCSAN, in case list debugging is on. */
  
  	INIT_LIST_HEAD(&sa->list);
  	sa->ptr = ptr;
  	sa->size = size;
  	sa->type = type;
  
  	if (!ctx->scoped_accesses.prev) /* Lazy initialize list head. */
  		INIT_LIST_HEAD(&ctx->scoped_accesses);
  	list_add(&sa->list, &ctx->scoped_accesses);
  
  	ctx->disable_count--;
  	return sa;
  }
  EXPORT_SYMBOL(kcsan_begin_scoped_access);
  
  void kcsan_end_scoped_access(struct kcsan_scoped_access *sa)
  {
  	struct kcsan_ctx *ctx = get_ctx();
  
  	if (WARN(!ctx->scoped_accesses.prev, "Unbalanced %s()?", __func__))
  		return;
  
  	ctx->disable_count++; /* Disable KCSAN, in case list debugging is on. */
  
  	list_del(&sa->list);
  	if (list_empty(&ctx->scoped_accesses))
  		/*
  		 * Ensure we do not enter kcsan_check_scoped_accesses()
  		 * slow-path if unnecessary, and avoids requiring list_empty()
  		 * in the fast-path (to avoid a READ_ONCE() and potential
  		 * uaccess warning).
  		 */
  		ctx->scoped_accesses.prev = NULL;
  
  	ctx->disable_count--;
  
  	__kcsan_check_access(sa->ptr, sa->size, sa->type);
  }
  EXPORT_SYMBOL(kcsan_end_scoped_access);

  void __kcsan_check_access(const volatile void *ptr, size_t size, int type)
  {
  	check_access(ptr, size, type);
  }
  EXPORT_SYMBOL(__kcsan_check_access);
  
  /*
   * KCSAN uses the same instrumentation that is emitted by supported compilers
   * for ThreadSanitizer (TSAN).
   *
   * When enabled, the compiler emits instrumentation calls (the functions
   * prefixed with "__tsan" below) for all loads and stores that it generated;
   * inline asm is not instrumented.
   *
   * Note that, not all supported compiler versions distinguish aligned/unaligned
   * accesses, but e.g. recent versions of Clang do. We simply alias the unaligned
   * version to the generic version, which can handle both.
   */
  
  #define DEFINE_TSAN_READ_WRITE(size)                                           \

  	void __tsan_read##size(void *ptr);                                     \

  	void __tsan_read##size(void *ptr)                                      \
  	{                                                                      \
  		check_access(ptr, size, 0);                                    \
  	}                                                                      \
  	EXPORT_SYMBOL(__tsan_read##size);                                      \
  	void __tsan_unaligned_read##size(void *ptr)                            \
  		__alias(__tsan_read##size);                                    \
  	EXPORT_SYMBOL(__tsan_unaligned_read##size);                            \

  	void __tsan_write##size(void *ptr);                                    \

  	void __tsan_write##size(void *ptr)                                     \
  	{                                                                      \
  		check_access(ptr, size, KCSAN_ACCESS_WRITE);                   \
  	}                                                                      \
  	EXPORT_SYMBOL(__tsan_write##size);                                     \
  	void __tsan_unaligned_write##size(void *ptr)                           \
  		__alias(__tsan_write##size);                                   \

  	EXPORT_SYMBOL(__tsan_unaligned_write##size);                           \
  	void __tsan_read_write##size(void *ptr);                               \
  	void __tsan_read_write##size(void *ptr)                                \
  	{                                                                      \
  		check_access(ptr, size,                                        \
  			     KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE);      \
  	}                                                                      \
  	EXPORT_SYMBOL(__tsan_read_write##size);                                \
  	void __tsan_unaligned_read_write##size(void *ptr)                      \
  		__alias(__tsan_read_write##size);                              \
  	EXPORT_SYMBOL(__tsan_unaligned_read_write##size)

  
  DEFINE_TSAN_READ_WRITE(1);
  DEFINE_TSAN_READ_WRITE(2);
  DEFINE_TSAN_READ_WRITE(4);
  DEFINE_TSAN_READ_WRITE(8);
  DEFINE_TSAN_READ_WRITE(16);

  void __tsan_read_range(void *ptr, size_t size);

  void __tsan_read_range(void *ptr, size_t size)
  {
  	check_access(ptr, size, 0);
  }
  EXPORT_SYMBOL(__tsan_read_range);

  void __tsan_write_range(void *ptr, size_t size);

  void __tsan_write_range(void *ptr, size_t size)
  {
  	check_access(ptr, size, KCSAN_ACCESS_WRITE);
  }
  EXPORT_SYMBOL(__tsan_write_range);
  
  /*

   * Use of explicit volatile is generally disallowed [1], however, volatile is
   * still used in various concurrent context, whether in low-level
   * synchronization primitives or for legacy reasons.
   * [1] https://lwn.net/Articles/233479/
   *
   * We only consider volatile accesses atomic if they are aligned and would pass
   * the size-check of compiletime_assert_rwonce_type().
   */
  #define DEFINE_TSAN_VOLATILE_READ_WRITE(size)                                  \

  	void __tsan_volatile_read##size(void *ptr);                            \

  	void __tsan_volatile_read##size(void *ptr)                             \
  	{                                                                      \
  		const bool is_atomic = size <= sizeof(long long) &&            \
  				       IS_ALIGNED((unsigned long)ptr, size);   \
  		if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic)      \
  			return;                                                \
  		check_access(ptr, size, is_atomic ? KCSAN_ACCESS_ATOMIC : 0);  \
  	}                                                                      \
  	EXPORT_SYMBOL(__tsan_volatile_read##size);                             \
  	void __tsan_unaligned_volatile_read##size(void *ptr)                   \
  		__alias(__tsan_volatile_read##size);                           \
  	EXPORT_SYMBOL(__tsan_unaligned_volatile_read##size);                   \

  	void __tsan_volatile_write##size(void *ptr);                           \

  	void __tsan_volatile_write##size(void *ptr)                            \
  	{                                                                      \
  		const bool is_atomic = size <= sizeof(long long) &&            \
  				       IS_ALIGNED((unsigned long)ptr, size);   \
  		if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic)      \
  			return;                                                \
  		check_access(ptr, size,                                        \
  			     KCSAN_ACCESS_WRITE |                              \
  				     (is_atomic ? KCSAN_ACCESS_ATOMIC : 0));   \
  	}                                                                      \
  	EXPORT_SYMBOL(__tsan_volatile_write##size);                            \
  	void __tsan_unaligned_volatile_write##size(void *ptr)                  \
  		__alias(__tsan_volatile_write##size);                          \
  	EXPORT_SYMBOL(__tsan_unaligned_volatile_write##size)
  
  DEFINE_TSAN_VOLATILE_READ_WRITE(1);
  DEFINE_TSAN_VOLATILE_READ_WRITE(2);
  DEFINE_TSAN_VOLATILE_READ_WRITE(4);
  DEFINE_TSAN_VOLATILE_READ_WRITE(8);
  DEFINE_TSAN_VOLATILE_READ_WRITE(16);
  
  /*

   * The below are not required by KCSAN, but can still be emitted by the
   * compiler.
   */

  void __tsan_func_entry(void *call_pc);

  void __tsan_func_entry(void *call_pc)
  {
  }
  EXPORT_SYMBOL(__tsan_func_entry);

  void __tsan_func_exit(void);

  void __tsan_func_exit(void)
  {
  }
  EXPORT_SYMBOL(__tsan_func_exit);

  void __tsan_init(void);

  void __tsan_init(void)
  {
  }
  EXPORT_SYMBOL(__tsan_init);

  
  /*
   * Instrumentation for atomic builtins (__atomic_*, __sync_*).
   *
   * Normal kernel code _should not_ be using them directly, but some
   * architectures may implement some or all atomics using the compilers'
   * builtins.
   *
   * Note: If an architecture decides to fully implement atomics using the
   * builtins, because they are implicitly instrumented by KCSAN (and KASAN,
   * etc.), implementing the ARCH_ATOMIC interface (to get instrumentation via
   * atomic-instrumented) is no longer necessary.
   *
   * TSAN instrumentation replaces atomic accesses with calls to any of the below
   * functions, whose job is to also execute the operation itself.
   */
  
  #define DEFINE_TSAN_ATOMIC_LOAD_STORE(bits)                                                        \
  	u##bits __tsan_atomic##bits##_load(const u##bits *ptr, int memorder);                      \
  	u##bits __tsan_atomic##bits##_load(const u##bits *ptr, int memorder)                       \
  	{                                                                                          \

  		if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) {                                    \
  			check_access(ptr, bits / BITS_PER_BYTE, KCSAN_ACCESS_ATOMIC);              \
  		}                                                                                  \

  		return __atomic_load_n(ptr, memorder);                                             \
  	}                                                                                          \
  	EXPORT_SYMBOL(__tsan_atomic##bits##_load);                                                 \
  	void __tsan_atomic##bits##_store(u##bits *ptr, u##bits v, int memorder);                   \
  	void __tsan_atomic##bits##_store(u##bits *ptr, u##bits v, int memorder)                    \
  	{                                                                                          \

  		if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) {                                    \
  			check_access(ptr, bits / BITS_PER_BYTE,                                    \
  				     KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC);                    \
  		}                                                                                  \

  		__atomic_store_n(ptr, v, memorder);                                                \
  	}                                                                                          \
  	EXPORT_SYMBOL(__tsan_atomic##bits##_store)
  
  #define DEFINE_TSAN_ATOMIC_RMW(op, bits, suffix)                                                   \
  	u##bits __tsan_atomic##bits##_##op(u##bits *ptr, u##bits v, int memorder);                 \
  	u##bits __tsan_atomic##bits##_##op(u##bits *ptr, u##bits v, int memorder)                  \
  	{                                                                                          \

  		if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) {                                    \
  			check_access(ptr, bits / BITS_PER_BYTE,                                    \
  				     KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE |                  \
  					     KCSAN_ACCESS_ATOMIC);                                 \
  		}                                                                                  \

  		return __atomic_##op##suffix(ptr, v, memorder);                                    \
  	}                                                                                          \
  	EXPORT_SYMBOL(__tsan_atomic##bits##_##op)
  
  /*
   * Note: CAS operations are always classified as write, even in case they
   * fail. We cannot perform check_access() after a write, as it might lead to
   * false positives, in cases such as:
   *
   *	T0: __atomic_compare_exchange_n(&p->flag, &old, 1, ...)
   *
   *	T1: if (__atomic_load_n(&p->flag, ...)) {
   *		modify *p;
   *		p->flag = 0;
   *	    }
   *
   * The only downside is that, if there are 3 threads, with one CAS that
   * succeeds, another CAS that fails, and an unmarked racing operation, we may
   * point at the wrong CAS as the source of the race. However, if we assume that
   * all CAS can succeed in some other execution, the data race is still valid.
   */
  #define DEFINE_TSAN_ATOMIC_CMPXCHG(bits, strength, weak)                                           \
  	int __tsan_atomic##bits##_compare_exchange_##strength(u##bits *ptr, u##bits *exp,          \
  							      u##bits val, int mo, int fail_mo);   \
  	int __tsan_atomic##bits##_compare_exchange_##strength(u##bits *ptr, u##bits *exp,          \
  							      u##bits val, int mo, int fail_mo)    \
  	{                                                                                          \

  		if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) {                                    \
  			check_access(ptr, bits / BITS_PER_BYTE,                                    \
  				     KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE |                  \
  					     KCSAN_ACCESS_ATOMIC);                                 \
  		}                                                                                  \

  		return __atomic_compare_exchange_n(ptr, exp, val, weak, mo, fail_mo);              \
  	}                                                                                          \
  	EXPORT_SYMBOL(__tsan_atomic##bits##_compare_exchange_##strength)
  
  #define DEFINE_TSAN_ATOMIC_CMPXCHG_VAL(bits)                                                       \
  	u##bits __tsan_atomic##bits##_compare_exchange_val(u##bits *ptr, u##bits exp, u##bits val, \
  							   int mo, int fail_mo);                   \
  	u##bits __tsan_atomic##bits##_compare_exchange_val(u##bits *ptr, u##bits exp, u##bits val, \
  							   int mo, int fail_mo)                    \
  	{                                                                                          \

  		if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) {                                    \
  			check_access(ptr, bits / BITS_PER_BYTE,                                    \
  				     KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE |                  \
  					     KCSAN_ACCESS_ATOMIC);                                 \
  		}                                                                                  \

  		__atomic_compare_exchange_n(ptr, &exp, val, 0, mo, fail_mo);                       \
  		return exp;                                                                        \
  	}                                                                                          \
  	EXPORT_SYMBOL(__tsan_atomic##bits##_compare_exchange_val)
  
  #define DEFINE_TSAN_ATOMIC_OPS(bits)                                                               \
  	DEFINE_TSAN_ATOMIC_LOAD_STORE(bits);                                                       \
  	DEFINE_TSAN_ATOMIC_RMW(exchange, bits, _n);                                                \
  	DEFINE_TSAN_ATOMIC_RMW(fetch_add, bits, );                                                 \
  	DEFINE_TSAN_ATOMIC_RMW(fetch_sub, bits, );                                                 \
  	DEFINE_TSAN_ATOMIC_RMW(fetch_and, bits, );                                                 \
  	DEFINE_TSAN_ATOMIC_RMW(fetch_or, bits, );                                                  \
  	DEFINE_TSAN_ATOMIC_RMW(fetch_xor, bits, );                                                 \
  	DEFINE_TSAN_ATOMIC_RMW(fetch_nand, bits, );                                                \
  	DEFINE_TSAN_ATOMIC_CMPXCHG(bits, strong, 0);                                               \
  	DEFINE_TSAN_ATOMIC_CMPXCHG(bits, weak, 1);                                                 \
  	DEFINE_TSAN_ATOMIC_CMPXCHG_VAL(bits)
  
  DEFINE_TSAN_ATOMIC_OPS(8);
  DEFINE_TSAN_ATOMIC_OPS(16);
  DEFINE_TSAN_ATOMIC_OPS(32);
  DEFINE_TSAN_ATOMIC_OPS(64);
  
  void __tsan_atomic_thread_fence(int memorder);
  void __tsan_atomic_thread_fence(int memorder)
  {
  	__atomic_thread_fence(memorder);
  }
  EXPORT_SYMBOL(__tsan_atomic_thread_fence);
  
  void __tsan_atomic_signal_fence(int memorder);
  void __tsan_atomic_signal_fence(int memorder) { }
  EXPORT_SYMBOL(__tsan_atomic_signal_fence);