From a7fed5c0431dbfa707037848830f980e0f93cfb3 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Sun, 15 May 2022 13:39:34 +0200 Subject: [PATCH] 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 Signed-off-by: Thomas Gleixner Signed-off-by: Borislav Petkov Link: https://lore.kernel.org/lkml/20220511234332.3654455-1-seanjc@google.com --- arch/x86/include/asm/nmi.h | 1 + arch/x86/kernel/nmi.c | 12 ++++++++---- 2 files changed, 9 insertions(+), 4 deletions(-) diff --git a/arch/x86/include/asm/nmi.h b/arch/x86/include/asm/nmi.h index 1cb9c17..5c5f1e5 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 e73f7df..cec0bfa 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); -- 2.7.4