kasan: don't call find_vm_area() in a PREEMPT_RT kernel

JIRA: https://issues.redhat.com/browse/RHEL-78135

commit ac7af1f
Author: Waiman Long <longman@redhat.com>
Date:   Mon Feb 17 15:44:02 2025 -0500

    kasan: don't call find_vm_area() in a PREEMPT_RT kernel

    The following bug report was found when running a PREEMPT_RT debug kernel.

     BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48
     in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 140605, name: kunit_try_catch
     preempt_count: 1, expected: 0

     Call trace:
      rt_spin_lock+0x70/0x140
      find_vmap_area+0x84/0x168
      find_vm_area+0x1c/0x50
      print_address_description.constprop.0+0x2a0/0x320
      print_report+0x108/0x1f8
      kasan_report+0x90/0xc8

    Since commit e30a036 ("kasan: make report_lock a raw spinlock"),
    report_lock was changed to raw_spinlock_t to fix another similar
    PREEMPT_RT problem.  That alone isn't enough to cover other corner cases.

    print_address_description() is always invoked under the report_lock.  The
    context under this lock is always atomic even on PREEMPT_RT.
    find_vm_area() acquires vmap_node::busy.lock which is a spinlock_t,
    becoming a sleeping lock on PREEMPT_RT and must not be acquired in atomic
    context.

    Don't invoke find_vm_area() on PREEMPT_RT and just print the address.
    Non-PREEMPT_RT builds remain unchanged.  Add a DEFINE_WAIT_OVERRIDE_MAP()
    macro to tell lockdep that this lock nesting is allowed because the
    PREEMPT_RT part (which is invalid) has been taken care of.  This macro was
    first introduced in commit 0cce06b ("debugobjects,locking: Annotate
    debug_object_fill_pool() wait type violation").

    Link: https://lkml.kernel.org/r/20250217204402.60533-1-longman@redhat.com
    Fixes: e30a036 ("kasan: make report_lock a raw spinlock")
    Signed-off-by: Waiman Long <longman@redhat.com>
    Suggested-by: Andrey Konovalov <andreyknvl@gmail.com>
    Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>
    Cc: Alexander Potapenko <glider@google.com>
    Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
    Cc: Dmitriy Vyukov <dvyukov@google.com>
    Cc: Steven Rostedt <rostedt@goodmis.org>
    Cc: Mariano Pache <npache@redhat.com>
    Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
    Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Signed-off-by: Luiz Capitulino <luizcap@redhat.com>

Author: luiz-cap

mm/kasan/report.c

@@ -370,6 +370,36 @@ static inline bool init_task_stack_addr(const void *addr)
 			sizeof(init_thread_union.stack));
 }
 
+/*
+ * This function is invoked with report_lock (a raw_spinlock) held. A
+ * PREEMPT_RT kernel cannot call find_vm_area() as it will acquire a sleeping
+ * rt_spinlock.
+ *
+ * For !RT kernel, the PROVE_RAW_LOCK_NESTING config option will print a
+ * lockdep warning for this raw_spinlock -> spinlock dependency. This config
+ * option is enabled by default to ensure better test coverage to expose this
+ * kind of RT kernel problem. This lockdep splat, however, can be suppressed
+ * by using DEFINE_WAIT_OVERRIDE_MAP() if it serves a useful purpose and the
+ * invalid PREEMPT_RT case has been taken care of.
+ */
+static inline struct vm_struct *kasan_find_vm_area(void *addr)
+{
+	static DEFINE_WAIT_OVERRIDE_MAP(vmalloc_map, LD_WAIT_SLEEP);
+	struct vm_struct *va;
+
+	if (IS_ENABLED(CONFIG_PREEMPT_RT))
+		return NULL;
+
+	/*
+	 * Suppress lockdep warning and fetch vmalloc area of the
+	 * offending address.
+	 */
+	lock_map_acquire_try(&vmalloc_map);
+	va = find_vm_area(addr);
+	lock_map_release(&vmalloc_map);
+	return va;
+}
+
 static void print_address_description(void *addr, u8 tag,
 				      struct kasan_report_info *info)
 {
@@ -399,7 +429,7 @@ static void print_address_description(void *addr, u8 tag,
 	}
 
 	if (is_vmalloc_addr(addr)) {
-		struct vm_struct *va = find_vm_area(addr);
+		struct vm_struct *va = kasan_find_vm_area(addr);
 
 		if (va) {
 			pr_err("The buggy address belongs to the virtual mapping at\n"
@@ -409,6 +439,8 @@ static void print_address_description(void *addr, u8 tag,
 			pr_err("\n");
 
 			page = vmalloc_to_page(addr);
+		} else {
+			pr_err("The buggy address %px belongs to a vmalloc virtual mapping\n", addr);
 		}
 	}