Commit 645f224e authored by Steven Rostedt (VMware)'s avatar Steven Rostedt (VMware)
Browse files

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: default avatarMasami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent 561ca669

kernel/kprobes.c

+21 −4
Original line number Diff line number Diff line
@@ -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;

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