linux-kernel - [PATCH] PCI: Avoid possible deadlock on pci_lock and p->pi

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]

Message-ID: <20170118234612.26157.95913.stgit@bhelgaas-glaptop.roam.corp.google.com>
Date:   Wed, 18 Jan 2017 17:46:12 -0600
From:   Bjorn Helgaas <bhelgaas@...gle.com>
To:     linux-pci@...r.kernel.org
Cc:     Jan Kiszka <jan.kiszka@...mens.com>, linux-kernel@...r.kernel.org,
        Matthew Wilcox <mawilcox@...rosoft.com>
Subject: [PATCH] PCI: Avoid possible deadlock on pci_lock and p->pi_lock

pci_lock is an IRQ-safe spinlock that protects all accesses to PCI
configuration space (see PCI_OP_READ() and PCI_OP_WRITE() in pci/access.c).

The pci_cfg_access_unlock() path acquires pci_lock, then p->pi_lock (inside
wake_up_all()).  According to lockdep, there is a possible path involving
snbep_uncore_pci_read_counter() that could acquire them in the reverse
order: acquiring p->pi_lock, then pci_lock, which could result in a
deadlock.  Lockdep details are in the bugzilla below.

Avoid the possible deadlock by dropping pci_lock before waking up any
config access waiters.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=192901
Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
---
 drivers/pci/access.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/access.c b/drivers/pci/access.c
index db239547fefd..68bd7201d8bc 100644
--- a/drivers/pci/access.c
+++ b/drivers/pci/access.c
@@ -684,8 +684,9 @@ void pci_cfg_access_unlock(struct pci_dev *dev)
 	WARN_ON(!dev->block_cfg_access);

 	dev->block_cfg_access = 0;
-	wake_up_all(&pci_cfg_wait);
 	raw_spin_unlock_irqrestore(&pci_lock, flags);
+
+	wake_up_all(&pci_cfg_wait);
 }
 EXPORT_SYMBOL_GPL(pci_cfg_access_unlock);