x86: Avoid race condition in pci_enable_msix()

Keep chip_data in create_irq_nr and destroy_irq.

When two drivers are setting up MSI-X at the same time via
pci_enable_msix() there is a race.  See this dmesg excerpt:

[   85.170610] ixgbe 0000:02:00.1: irq 97 for MSI/MSI-X
[   85.170611]   alloc irq_desc for 99 on node -1
[   85.170613] igb 0000:08:00.1: irq 98 for MSI/MSI-X
[   85.170614]   alloc kstat_irqs on node -1
[   85.170616] alloc irq_2_iommu on node -1
[   85.170617]   alloc irq_desc for 100 on node -1
[   85.170619]   alloc kstat_irqs on node -1
[   85.170621] alloc irq_2_iommu on node -1
[   85.170625] ixgbe 0000:02:00.1: irq 99 for MSI/MSI-X
[   85.170626]   alloc irq_desc for 101 on node -1
[   85.170628] igb 0000:08:00.1: irq 100 for MSI/MSI-X
[   85.170630]   alloc kstat_irqs on node -1
[   85.170631] alloc irq_2_iommu on node -1
[   85.170635]   alloc irq_desc for 102 on node -1
[   85.170636]   alloc kstat_irqs on node -1
[   85.170639] alloc irq_2_iommu on node -1
[   85.170646] BUG: unable to handle kernel NULL pointer dereference
at 0000000000000088

As you can see igb and ixgbe are both alternating on create_irq_nr()
via pci_enable_msix() in their probe function.

ixgbe: While looping through irq_desc_ptrs[] via create_irq_nr() ixgbe
choses irq_desc_ptrs[102] and exits the loop, drops vector_lock and
calls dynamic_irq_init. Then it sets irq_desc_ptrs[102]->chip_data =
NULL via dynamic_irq_init().

igb: Grabs the vector_lock now and starts looping over irq_desc_ptrs[]
via create_irq_nr(). It gets to irq_desc_ptrs[102] and does this:

	cfg_new = irq_desc_ptrs[102]->chip_data;
	if (cfg_new->vector != 0)
		continue;

This hits the NULL deref.

Another possible race exists via pci_disable_msix() in a driver or in
the number of error paths that call free_msi_irqs():

destroy_irq()
dynamic_irq_cleanup() which sets desc->chip_data = NULL
...race window...
desc->chip_data = cfg;

Remove the save and restore code for cfg in create_irq_nr() and
destroy_irq() and take the desc->lock when checking the irq_cfg.

Reported-and-analyzed-by: Brandon Philips <bphilips@suse.de>
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
LKML-Reference: <1265793639-15071-3-git-send-email-yinghai@kernel.org>
Signed-off-by: Brandon Phililps <bphilips@suse.de>
Cc: stable@kernel.org
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

1 files changed, 5 insertions, 13 deletions

diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
index 53243ca7816d..c86591b906fa 100644
--- a/arch/x86/kernel/apic/io_apic.c
+++ b/arch/x86/kernel/apic/io_apic.c
@@ -3228,12 +3228,9 @@ unsigned int create_irq_nr(unsigned int irq_want, int node)
         }
         spin_unlock_irqrestore(&vector_lock, flags);
 
-        if (irq > 0) {
-                dynamic_irq_init(irq);
-                /* restore it, in case dynamic_irq_init clear it */
-                if (desc_new)
-                        desc_new->chip_data = cfg_new;
-        }
+        if (irq > 0)
+                dynamic_irq_init_keep_chip_data(irq);
+
         return irq;
 }
 
@@ -3256,17 +3253,12 @@ void destroy_irq(unsigned int irq)
 {
         unsigned long flags;
         struct irq_cfg *cfg;
-        struct irq_desc *desc;
 
-        /* store it, in case dynamic_irq_cleanup clear it */
-        desc = irq_to_desc(irq);
-        cfg = desc->chip_data;
-        dynamic_irq_cleanup(irq);
-        /* connect back irq_cfg */
-        desc->chip_data = cfg;
+        dynamic_irq_cleanup_keep_chip_data(irq);
 
         free_irte(irq);
         spin_lock_irqsave(&vector_lock, flags);
+        cfg = irq_to_desc(irq)->chip_data;
         __clear_irq_vector(irq, cfg);
         spin_unlock_irqrestore(&vector_lock, flags);
 }