kprobes: Tell lockdep about kprobe nesting

commit 645f224e7ba2f4200bf163153d384ceb0de5462e upstream.

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: stable@vger.kernel.org # 5.9.x
Cc: Peter Zijlstra <peterz@infradead.org>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index b885d884603d95b54621726e536825077497ba9f..1b7fd1ab8ddcd8073eabd27bb410223c3bddfe3e 100644 (file)
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1250,7 +1250,13 @@ __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);
 
@@ -1259,7 +1265,13 @@ 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);
 
@@ -1942,7 +1954,12 @@ 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);
@@ -1953,7 +1970,7 @@ 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;