linux-kernel - [PATCH] locking/pvqspinlock: Fix kernel panic in locking-selftest

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: Windows password security audit tool. GUI, reports in PDF.

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

Date:	Sat, 11 Jul 2015 21:19:19 -0400
From:	Waiman Long <Waiman.Long@...com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Waiman Long <Waiman.Long@...com>
Subject: [PATCH] locking/pvqspinlock: Fix kernel panic in locking-selftest

Enabling locking-selftest in a VM guest may cause the following
kernel panic:

kernel BUG at .../kernel/locking/qspinlock_paravirt.h:137!

This is due to the fact that the pvqspinlock unlock function is
expecting either a _Q_LOCKED_VAL or _Q_SLOW_VAL in the lock byte. This
patch prevents that bug report by ignoring it when debug_locks_silent
is set. Otherwise, a warning will be printed if it contains an
unexpected value.

With this patch applied, the kernel locking-selftest completed without
any noise.

Signed-off-by: Waiman Long <Waiman.Long@...com>
---
 kernel/locking/qspinlock_paravirt.h |   12 +++++++++++-
 1 files changed, 11 insertions(+), 1 deletions(-)

diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h
index 04ab181..15d3733 100644
--- a/kernel/locking/qspinlock_paravirt.h
+++ b/kernel/locking/qspinlock_paravirt.h
@@ -4,6 +4,7 @@
 
 #include <linux/hash.h>
 #include <linux/bootmem.h>
+#include <linux/debug_locks.h>
 
 /*
  * Implement paravirt qspinlocks; the general idea is to halt the vcpus instead
@@ -286,15 +287,24 @@ __visible void __pv_queued_spin_unlock(struct qspinlock *lock)
 {
 	struct __qspinlock *l = (void *)lock;
 	struct pv_node *node;
+	u8 lockval = cmpxchg(&l->locked, _Q_LOCKED_VAL, 0);
 
 	/*
 	 * We must not unlock if SLOW, because in that case we must first
 	 * unhash. Otherwise it would be possible to have multiple @lock
 	 * entries, which would be BAD.
 	 */
-	if (likely(cmpxchg(&l->locked, _Q_LOCKED_VAL, 0) == _Q_LOCKED_VAL))
+	if (likely(lockval == _Q_LOCKED_VAL))
 		return;
 
+	if (unlikely(lockval != _Q_SLOW_VAL)) {
+		if (debug_locks_silent)
+			return;
+		WARN(1, "pvqspinlock: lock 0x%lx has corrupted value 0x%x!\n",
+		    (unsigned long)lock, atomic_read(&lock->val));
+		return;
+	}
+
 	/*
 	 * Since the above failed to release, this must be the SLOW path.
 	 * Therefore start by looking up the blocked node and unhashing it.
-- 
1.7.1

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/