[PATCH] iommu/dmar: ignore devices with out-of-spec domain number

[PATCH] iommu/dmar: ignore devices with out-of-spec domain number

[Daniel Drake]

VMD subdevices are created with a PCI domain ID of 0x10000 or
higher.

These subdevices are also handled like all other PCI devices by
dmar_pci_bus_notifier().

However, when dmar_alloc_pci_notify_info() take records of such devices,
it will truncate the domain ID to a u16 value (in info->seg).
The device at (e.g.) 10000:00:02.0 is then treated by the DMAR code as if
it is 0000:00:02.0.

In the unlucky event that a real device also exists at 0000:00:02.0 and
also has a device-specific entry in the DMAR table,
dmar_insert_dev_scope() will crash on:
   BUG_ON(i >= devices_cnt);

That's basically a sanity check that only one PCI device matches a
single DMAR entry; in this case we seem to have two matching devices.

Fix this by ignoring devices that have a domain number higher than
what can be looked up in the DMAR table.

This problem was carefully diagnosed by Jian-Hong Pan.

Signed-off-by: Daniel Drake <drake@endlessm.com>
---

Notes:
    This problem was detected with a non-upstream patch
    "PCI: Add Intel remapped NVMe device support"
    (https://marc.info/?l=linux-ide&m=156015271021615&w=2)
    
    This patch creates PCI devices in the same way as VMD, and hence
    I believe VMD would hit the same problem that we encountered here, when
    a VMD-using product comes along that meets the mentioned conditions.
    
    However this hasn't actually been tested on VMD (don't have the hardware)
    so if I've missed anything and/or it's not a real issue then feel free to
    drop this patch.

 drivers/iommu/dmar.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/iommu/dmar.c b/drivers/iommu/dmar.c
index 071bb42bbbc5..8f94c817a7b5 100644
--- a/drivers/iommu/dmar.c
+++ b/drivers/iommu/dmar.c
@@ -28,6 +28,7 @@
 #include <linux/slab.h>
 #include <linux/iommu.h>
 #include <linux/numa.h>
+#include <linux/limits.h>
 #include <asm/irq_remapping.h>
 #include <asm/iommu_table.h>
 
@@ -128,6 +129,13 @@ dmar_alloc_pci_notify_info(struct pci_dev *dev, unsigned long event)
 
 	BUG_ON(dev->is_virtfn);
 
+	/*
+	 * Ignore devices that have a domain number higher than what can
+	 * be looked up in DMAR, e.g. VMD subdevices with domain 0x10000
+	 */
+	if (pci_domain_nr(dev->bus) > U16_MAX)
+		return NULL;
+
 	/* Only generate path[] for device addition event */
 	if (event == BUS_NOTIFY_ADD_DEVICE)
 		for (tmp = dev; tmp; tmp = tmp->bus->self)
-- 
2.20.1

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Re: [PATCH] iommu/dmar: ignore devices with out-of-spec domain number

[Lu Baolu]

Hi,

On 2020/2/11 17:03, Daniel Drake wrote:
> VMD subdevices are created with a PCI domain ID of 0x10000 or
> higher.
> 
> These subdevices are also handled like all other PCI devices by
> dmar_pci_bus_notifier().
> 
> However, when dmar_alloc_pci_notify_info() take records of such devices,
> it will truncate the domain ID to a u16 value (in info->seg).
> The device at (e.g.) 10000:00:02.0 is then treated by the DMAR code as if
> it is 0000:00:02.0.
> 
> In the unlucky event that a real device also exists at 0000:00:02.0 and
> also has a device-specific entry in the DMAR table,
> dmar_insert_dev_scope() will crash on:
>     BUG_ON(i >= devices_cnt);
> 
> That's basically a sanity check that only one PCI device matches a
> single DMAR entry; in this case we seem to have two matching devices.
> 
> Fix this by ignoring devices that have a domain number higher than
> what can be looked up in the DMAR table.
> 
> This problem was carefully diagnosed by Jian-Hong Pan.
> 
> Signed-off-by: Daniel Drake<drake@endlessm.com>

Queued for v5.7. Thanks!

Best regards,
baolu
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