kprobes: Remove NMI context check (e03b4a08) · Commits · 戴 / test

The in_nmi() check in pre_handler_kretprobe() is meant to avoid recursion, and blindly assumes that anything NMI is recursive. However, since commit: ("kretprobe: Prevent triggering kretprobe from within kprobe_flush_task") there is a better way to detect and avoid actual recursion. By setting a dummy kprobe, any actual exceptions will terminate early (by trying to handle the dummy kprobe), and recursion will not happen. Employ this to avoid the kretprobe_table_lock() recursion, replacing the over-eager in_nmi() check. Signed-off-by:

Masami Hiramatsu <mhiramat@kernel.org> Signed-off-by:

Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by:

Ingo Molnar <mingo@kernel.org> Link: https://lkml.kernel.org/r/159870615628.1229682.6087311596892125907.stgit@devnote2

kernel/kprobes.c

+4 −12

Original line number	Diff line number	Diff line
		@@ -1359,7 +1359,8 @@ static void cleanup_rp_inst(struct kretprobe *rp)
		struct hlist_node *next;
		struct hlist_head *head;

		/* No race here */
		/* To avoid recursive kretprobe by NMI, set kprobe busy here */
		kprobe_busy_begin();
		for (hash = 0; hash < KPROBE_TABLE_SIZE; hash++) {
		kretprobe_table_lock(hash, &flags);
		head = &kretprobe_inst_table[hash];
		@@ -1369,6 +1370,8 @@ static void cleanup_rp_inst(struct kretprobe *rp)
		}
		kretprobe_table_unlock(hash, &flags);
		}
		kprobe_busy_end();

		free_rp_inst(rp);
		}
		NOKPROBE_SYMBOL(cleanup_rp_inst);
		@@ -2035,17 +2038,6 @@ static int pre_handler_kretprobe(struct kprobe p, struct pt_regs regs)
		unsigned long hash, flags = 0;
		struct kretprobe_instance *ri;

		/*
		* To avoid deadlocks, prohibit return probing in NMI contexts,
		* just skip the probe and increase the (inexact) 'nmissed'
		* statistical counter, so that the user is informed that
		* something happened:
		*/
		if (unlikely(in_nmi())) {
		rp->nmissed++;
		return 0;
		}

		/* 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);

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