Commit 698361bc authored by Tianchen Ding's avatar Tianchen Ding Committed by Linus Torvalds
Browse files

kfence: allow re-enabling KFENCE after system startup 

Patch series "provide the flexibility to enable KFENCE", v3.

If CONFIG_CONTIG_ALLOC is not supported, we fallback to try
alloc_pages_exact().  Allocating pages in this way has limits about
MAX_ORDER (default 11).  So we will not support allocating kfence pool
after system startup with a large KFENCE_NUM_OBJECTS.

When handling failures in kfence_init_pool_late(), we pair
free_pages_exact() to alloc_pages_exact() for compatibility consideration,
though it actually does the same as free_contig_range().

This patch (of 2):

If once KFENCE is disabled by:
echo 0 > /sys/module/kfence/parameters/sample_interval
KFENCE could never be re-enabled until next rebooting.

Allow re-enabling it by writing a positive num to sample_interval.

Link: https://lkml.kernel.org/r/20220307074516.6920-1-dtcccc@linux.alibaba.com
Link: https://lkml.kernel.org/r/20220307074516.6920-2-dtcccc@linux.alibaba.com


Signed-off-by: default avatarTianchen Ding <dtcccc@linux.alibaba.com>
Reviewed-by: default avatarMarco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 56eb8e94

mm/kfence/core.c

+18 −3
Original line number Diff line number Diff line
@@ -38,14 +38,17 @@ 
#define KFENCE_WARN_ON(cond)                                                   \

	({                                                                     \

		const bool __cond = WARN_ON(cond);                             \

		if (unlikely(__cond))                                          \

		if (unlikely(__cond)) {                                        \

			WRITE_ONCE(kfence_enabled, false);                     \

			disabled_by_warn = true;                               \

		}                                                              \

		__cond;                                                        \

	})



/* === Data ================================================================= */



static bool kfence_enabled __read_mostly;

static bool disabled_by_warn __read_mostly;



unsigned long kfence_sample_interval __read_mostly = CONFIG_KFENCE_SAMPLE_INTERVAL;

EXPORT_SYMBOL_GPL(kfence_sample_interval); /* Export for test modules. */
@@ -55,6 +58,7 @@ EXPORT_SYMBOL_GPL(kfence_sample_interval); /* Export for test modules. */ 
#endif

#define MODULE_PARAM_PREFIX "kfence."



static int kfence_enable_late(void);

static int param_set_sample_interval(const char *val, const struct kernel_param *kp)

{

	unsigned long num;
@@ -65,10 +69,11 @@ static int param_set_sample_interval(const char *val, const struct kernel_param 


	if (!num) /* Using 0 to indicate KFENCE is disabled. */

		WRITE_ONCE(kfence_enabled, false);

	else if (!READ_ONCE(kfence_enabled) && system_state != SYSTEM_BOOTING)

		return -EINVAL; /* Cannot (re-)enable KFENCE on-the-fly. */



	*((unsigned long *)kp->arg) = num;



	if (num && !READ_ONCE(kfence_enabled) && system_state != SYSTEM_BOOTING)

		return disabled_by_warn ? -EINVAL : kfence_enable_late();

	return 0;

}
@@ -787,6 +792,16 @@ void __init kfence_init(void) 
		(void *)(__kfence_pool + KFENCE_POOL_SIZE));

}



static int kfence_enable_late(void)

{

	if (!__kfence_pool)

		return -EINVAL;



	WRITE_ONCE(kfence_enabled, true);

	queue_delayed_work(system_unbound_wq, &kfence_timer, 0);

	return 0;

}



void kfence_shutdown_cache(struct kmem_cache *s)

{

	unsigned long flags;