95 lines
2.7 KiB
C
95 lines
2.7 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
|
|
/*
|
|
* Special rules for ignoring entire classes of data-racy memory accesses. None
|
|
* of the rules here imply that such data races are generally safe!
|
|
*
|
|
* All rules in this file can be configured via CONFIG_KCSAN_PERMISSIVE. Keep
|
|
* them separate from core code to make it easier to audit.
|
|
*
|
|
* Copyright (C) 2019, Google LLC.
|
|
*/
|
|
|
|
#ifndef _KERNEL_KCSAN_PERMISSIVE_H
|
|
#define _KERNEL_KCSAN_PERMISSIVE_H
|
|
|
|
#include <linux/bitops.h>
|
|
#include <linux/sched.h>
|
|
#include <linux/types.h>
|
|
|
|
/*
|
|
* Access ignore rules based on address.
|
|
*/
|
|
static __always_inline bool kcsan_ignore_address(const volatile void *ptr)
|
|
{
|
|
if (!IS_ENABLED(CONFIG_KCSAN_PERMISSIVE))
|
|
return false;
|
|
|
|
/*
|
|
* Data-racy bitops on current->flags are too common, ignore completely
|
|
* for now.
|
|
*/
|
|
return ptr == ¤t->flags;
|
|
}
|
|
|
|
/*
|
|
* Data race ignore rules based on access type and value change patterns.
|
|
*/
|
|
static bool
|
|
kcsan_ignore_data_race(size_t size, int type, u64 old, u64 new, u64 diff)
|
|
{
|
|
if (!IS_ENABLED(CONFIG_KCSAN_PERMISSIVE))
|
|
return false;
|
|
|
|
/*
|
|
* Rules here are only for plain read accesses, so that we still report
|
|
* data races between plain read-write accesses.
|
|
*/
|
|
if (type || size > sizeof(long))
|
|
return false;
|
|
|
|
/*
|
|
* A common pattern is checking/setting just 1 bit in a variable; for
|
|
* example:
|
|
*
|
|
* if (flags & SOME_FLAG) { ... }
|
|
*
|
|
* and elsewhere flags is updated concurrently:
|
|
*
|
|
* flags |= SOME_OTHER_FLAG; // just 1 bit
|
|
*
|
|
* While it is still recommended that such accesses be marked
|
|
* appropriately, in many cases these types of data races are so common
|
|
* that marking them all is often unrealistic and left to maintainer
|
|
* preference.
|
|
*
|
|
* The assumption in all cases is that with all known compiler
|
|
* optimizations (including those that tear accesses), because no more
|
|
* than 1 bit changed, the plain accesses are safe despite the presence
|
|
* of data races.
|
|
*
|
|
* The rules here will ignore the data races if we observe no more than
|
|
* 1 bit changed.
|
|
*
|
|
* Of course many operations can effecively change just 1 bit, but the
|
|
* general assuption that data races involving 1-bit changes can be
|
|
* tolerated still applies.
|
|
*
|
|
* And in case a true bug is missed, the bug likely manifests as a
|
|
* reportable data race elsewhere.
|
|
*/
|
|
if (hweight64(diff) == 1) {
|
|
/*
|
|
* Exception: Report data races where the values look like
|
|
* ordinary booleans (one of them was 0 and the 0th bit was
|
|
* changed) More often than not, they come with interesting
|
|
* memory ordering requirements, so let's report them.
|
|
*/
|
|
if (!((!old || !new) && diff == 1))
|
|
return true;
|
|
}
|
|
|
|
return false;
|
|
}
|
|
|
|
#endif /* _KERNEL_KCSAN_PERMISSIVE_H */
|