kprobes: Tell lockdep about kprobe nesting

Since the kprobe handlers have protection that prohibits other handlers from
executing in other contexts (like if an NMI comes in while processing a
kprobe, and executes the same kprobe, it will get fail with a "busy"
return). Lockdep is unaware of this protection. Use lockdep's nesting api to
differentiate between locks taken in INT3 context and other context to
suppress the false warnings.

Link: https://lore.kernel.org/r/20201102160234.fa0ae70915ad9e2b21c08b85@kernel.org
Cc: Peter Zijlstra <peterz@infradead.org>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 8a12a25fa40d5e1c12303a6d395949d0ad4c135d..41fdbb7953c60f878049b2a5807abb4aecf95320 100644 (file)
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1249,7 +1249,13 @@ __acquires(hlist_lock)
 
        *head = &kretprobe_inst_table[hash];
        hlist_lock = kretprobe_table_lock_ptr(hash);
-       raw_spin_lock_irqsave(hlist_lock, *flags);
+       /*
+        * Nested is a workaround that will soon not be needed.
+        * There's other protections that make sure the same lock
+        * is not taken on the same CPU that lockdep is unaware of.
+        * Differentiate when it is taken in NMI context.
+        */
+       raw_spin_lock_irqsave_nested(hlist_lock, *flags, !!in_nmi());
 }
 NOKPROBE_SYMBOL(kretprobe_hash_lock);
 
@@ -1258,7 +1264,13 @@ static void kretprobe_table_lock(unsigned long hash,
 __acquires(hlist_lock)
 {
        raw_spinlock_t *hlist_lock = kretprobe_table_lock_ptr(hash);
-       raw_spin_lock_irqsave(hlist_lock, *flags);
+       /*
+        * Nested is a workaround that will soon not be needed.
+        * There's other protections that make sure the same lock
+        * is not taken on the same CPU that lockdep is unaware of.
+        * Differentiate when it is taken in NMI context.
+        */
+       raw_spin_lock_irqsave_nested(hlist_lock, *flags, !!in_nmi());
 }
 NOKPROBE_SYMBOL(kretprobe_table_lock);
 
@@ -2028,7 +2040,12 @@ static int pre_handler_kretprobe(struct kprobe *p, struct pt_regs *regs)
 
        /* TODO: consider to only swap the RA after the last pre_handler fired */
        hash = hash_ptr(current, KPROBE_HASH_BITS);
-       raw_spin_lock_irqsave(&rp->lock, flags);
+       /*
+        * Nested is a workaround that will soon not be needed.
+        * There's other protections that make sure the same lock
+        * is not taken on the same CPU that lockdep is unaware of.
+        */
+       raw_spin_lock_irqsave_nested(&rp->lock, flags, 1);
        if (!hlist_empty(&rp->free_instances)) {
                ri = hlist_entry(rp->free_instances.first,
                                struct kretprobe_instance, hlist);
@@ -2039,7 +2056,7 @@ static int pre_handler_kretprobe(struct kprobe *p, struct pt_regs *regs)
                ri->task = current;
 
                if (rp->entry_handler && rp->entry_handler(ri, regs)) {
-                       raw_spin_lock_irqsave(&rp->lock, flags);
+                       raw_spin_lock_irqsave_nested(&rp->lock, flags, 1);
                        hlist_add_head(&ri->hlist, &rp->free_instances);
                        raw_spin_unlock_irqrestore(&rp->lock, flags);
                        return 0;