kfence: fix KASAN HW tags bypass via runtime sample_interval change

If a user writes a non-zero value to the sample_interval module parameter
at runtime, the missing KASAN HW tags check in the late init path allows
KFENCE to be enabled alongside KASAN HW tags, bypassing the boot
restriction.

This patch adds the missing check to param_set_sample_interval() to reject
the parameter change if KASAN HW tags are enabled.

Link: https://lore.kernel.org/20260507095237.741017-1-glider@google.com
Fixes: 09833d99db36 ("mm/kfence: disable KFENCE upon KASAN HW tags enablement")
Signed-off-by: Alexander Potapenko <glider@google.com>
Cc: Marco Elver <elver@google.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Pimyn Girgis <pimyn@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index 655dc5ce32409e47b469fcd6088174b23ea7a67f..ee6ae01de5aef27526721b578b92f4f2c52d9e60 100644 (file)
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -77,6 +77,11 @@ static int param_set_sample_interval(const char *val, const struct kernel_param
                WRITE_ONCE(kfence_enabled, false);
        }
 
+       if (num && kasan_hw_tags_enabled()) {
+               pr_info("disabled as KASAN HW tags are enabled\n");
+               return -EINVAL;
+       }
+
        *((unsigned long *)kp->arg) = num;
 
        if (num && !READ_ONCE(kfence_enabled) && system_state != SYSTEM_BOOTING)