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 1cb9c17..5c5f1e5 100644 (file)
--- 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 e73f7df..cec0bfa 100644 (file)
--- 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);