linux-kernel - [PATCH 5.18 039/339] misc/pvpanic: Convert regular spinlock into trylock on panic path

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20220613094927.705605246@linuxfoundation.org>
Date:   Mon, 13 Jun 2022 12:07:44 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        Mihai Carabas <mihai.carabas@...cle.com>,
        Shile Zhang <shile.zhang@...ux.alibaba.com>,
        Wang ShaoBo <bobo.shaobowang@...wei.com>,
        zhenwei pi <pizhenwei@...edance.com>,
        "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.18 039/339] misc/pvpanic: Convert regular spinlock into trylock on panic path

From: Guilherme G. Piccoli <gpiccoli@...lia.com>

[ Upstream commit e918c10265ef2bc82ce8a6fed6d8123d09ec1db3 ]

The pvpanic driver relies on panic notifiers to execute a callback
on panic event. Such function is executed in atomic context - the
panic function disables local IRQs, preemption and all other CPUs
that aren't running the panic code.

With that said, it's dangerous to use regular spinlocks in such path,
as introduced by commit b3c0f8774668 ("misc/pvpanic: probe multiple instances").
This patch fixes that by replacing regular spinlocks with the trylock
safer approach.

It also fixes an old comment (about a long gone framebuffer code) and
the notifier priority - we should execute hypervisor notifiers early,
deferring this way the panic action to the hypervisor, as expected by
the users that are setting up pvpanic.

Fixes: b3c0f8774668 ("misc/pvpanic: probe multiple instances")
Cc: Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc: Mihai Carabas <mihai.carabas@...cle.com>
Cc: Shile Zhang <shile.zhang@...ux.alibaba.com>
Cc: Wang ShaoBo <bobo.shaobowang@...wei.com>
Cc: zhenwei pi <pizhenwei@...edance.com>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@...lia.com>
Link: https://lore.kernel.org/r/20220427224924.592546-6-gpiccoli@igalia.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/misc/pvpanic/pvpanic.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/misc/pvpanic/pvpanic.c b/drivers/misc/pvpanic/pvpanic.c
index 4b8f1c7d726d..049a12006348 100644
--- a/drivers/misc/pvpanic/pvpanic.c
+++ b/drivers/misc/pvpanic/pvpanic.c
@@ -34,7 +34,9 @@ pvpanic_send_event(unsigned int event)
 {
 	struct pvpanic_instance *pi_cur;
 
-	spin_lock(&pvpanic_lock);
+	if (!spin_trylock(&pvpanic_lock))
+		return;
+
 	list_for_each_entry(pi_cur, &pvpanic_list, list) {
 		if (event & pi_cur->capability & pi_cur->events)
 			iowrite8(event, pi_cur->base);
@@ -55,9 +57,13 @@ pvpanic_panic_notify(struct notifier_block *nb, unsigned long code, void *unused
 	return NOTIFY_DONE;
 }
 
+/*
+ * Call our notifier very early on panic, deferring the
+ * action taken to the hypervisor.
+ */
 static struct notifier_block pvpanic_panic_nb = {
 	.notifier_call = pvpanic_panic_notify,
-	.priority = 1, /* let this called before broken drm_fb_helper() */
+	.priority = INT_MAX,
 };
 
 static void pvpanic_remove(void *param)
-- 
2.35.1