From: Thomas Gleixner <tglx@linutronix.de>
Date: Sun, 15 May 2022 11:39:34 +0000 (+0200)
Subject: x86/nmi: Make register_nmi_handler() more robust
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=a7fed5c0431dbfa707037848830f980e0f93cfb3;p=linux.git

x86/nmi: Make register_nmi_handler() more robust

register_nmi_handler() has no sanity check whether a handler has been
registered already. Such an unintended double-add leads to list corruption
and hard to diagnose problems during the next NMI handling.

Init the list head in the static NMI action struct and check it for being
empty in register_nmi_handler().

  [ bp: Fixups. ]

Reported-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/lkml/20220511234332.3654455-1-seanjc@google.com
---

diff --git a/arch/x86/include/asm/nmi.h b/arch/x86/include/asm/nmi.h
index 1cb9c17a4cb4b..5c5f1e56c4048 100644
--- a/arch/x86/include/asm/nmi.h
+++ b/arch/x86/include/asm/nmi.h
@@ -47,6 +47,7 @@ struct nmiaction {
 #define register_nmi_handler(t, fn, fg, n, init...)	\
 ({							\
 	static struct nmiaction init fn##_na = {	\
+		.list = LIST_HEAD_INIT(fn##_na.list),	\
 		.handler = (fn),			\
 		.name = (n),				\
 		.flags = (fg),				\
diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c
index e73f7df362f5d..cec0bfa3bc04f 100644
--- a/arch/x86/kernel/nmi.c
+++ b/arch/x86/kernel/nmi.c
@@ -157,7 +157,7 @@ int __register_nmi_handler(unsigned int type, struct nmiaction *action)
 	struct nmi_desc *desc = nmi_to_desc(type);
 	unsigned long flags;
 
-	if (!action->handler)
+	if (WARN_ON_ONCE(!action->handler || !list_empty(&action->list)))
 		return -EINVAL;
 
 	raw_spin_lock_irqsave(&desc->lock, flags);
@@ -177,7 +177,7 @@ int __register_nmi_handler(unsigned int type, struct nmiaction *action)
 		list_add_rcu(&action->list, &desc->head);
 	else
 		list_add_tail_rcu(&action->list, &desc->head);
-	
+
 	raw_spin_unlock_irqrestore(&desc->lock, flags);
 	return 0;
 }
@@ -186,7 +186,7 @@ EXPORT_SYMBOL(__register_nmi_handler);
 void unregister_nmi_handler(unsigned int type, const char *name)
 {
 	struct nmi_desc *desc = nmi_to_desc(type);
-	struct nmiaction *n;
+	struct nmiaction *n, *found = NULL;
 	unsigned long flags;
 
 	raw_spin_lock_irqsave(&desc->lock, flags);
@@ -200,12 +200,16 @@ void unregister_nmi_handler(unsigned int type, const char *name)
 			WARN(in_nmi(),
 				"Trying to free NMI (%s) from NMI context!\n", n->name);
 			list_del_rcu(&n->list);
+			found = n;
 			break;
 		}
 	}
 
 	raw_spin_unlock_irqrestore(&desc->lock, flags);
-	synchronize_rcu();
+	if (found) {
+		synchronize_rcu();
+		INIT_LIST_HEAD(&found->list);
+	}
 }
 EXPORT_SYMBOL_GPL(unregister_nmi_handler);