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Subject[PATCH v3 1/2] kfence: Allow re-enabling KFENCE after system startup
Date
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.

Signed-off-by: Tianchen Ding <dtcccc@linux.alibaba.com>
---
mm/kfence/core.c | 21 ++++++++++++++++++---
1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index 13128fa13062..caa4e84c8b79 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -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;
--
2.27.0
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