PCI/MSI: Cache the MSIX table size

A malicious device can change its MSIX table size between the table
ioremap() and subsequent accesses, resulting in a page fault:

> BUG: unable to handle page fault for address: ffffc9000005a00c
> #PF: supervisor write access in kernel mode
> #PF: error_code(0x0002) - not-present page
> PGD 5800067 P4D 5800067 PUD 645c067 PMD 645d067 PTE 0
> Oops: 0002 [#1] PREEMPT SMP KASAN
> CPU: 2 PID: 1 Comm: swapper/0 Not tainted 5.17.0-rc1-00148-g16fc64ddb0ef-dirty torvalds#249
> RIP: 0010:__pci_write_msi_msg+0x3d9/0x3f0
> Call Trace:
>  <TASK>
>  pci_msi_domain_write_msg+0x61/0x70
>  msi_domain_activate+0xe0/0x110
>  __irq_domain_activate_irq+0x87/0xc0
>  irq_domain_activate_irq+0x69/0x90
>  __msi_domain_alloc_irqs+0x31a/0x5e0
>  msi_domain_alloc_irqs_descs_locked+0x7b/0x110
>  pci_msi_setup_msi_irqs+0x55/0x70
>  __pci_enable_msix_range+0x57a/0x78f
>  pci_alloc_irq_vectors_affinity.cold+0x1a/0x2e
>  vp_find_vqs_msix+0x17e/0x790
>  vp_find_vqs+0x3e/0x270
>  virtnet_find_vqs+0x2b4/0x560
>  virtnet_probe+0x734/0x1030
>  virtio_dev_probe+0x25c/0x3c0
>  really_probe+0x37d/0x660
>  __driver_probe_device+0x19e/0x230
>  driver_probe_device+0x4e/0xf0
>  __driver_attach+0xfe/0x270
>  bus_for_each_dev+0xff/0x150
>  driver_attach+0x2d/0x40
>  bus_add_driver+0x242/0x300
>  driver_register+0x119/0x1a0
>  register_virtio_driver+0x41/0x70
>  virtio_net_driver_init+0x74/0x9b
>  do_one_initcall+0xcc/0x400
>  kernel_init_freeable+0x3db/0x468
>  kernel_init+0x1e/0x150
>  ret_from_fork+0x22/0x30
>  </TASK>

To avoid this, cache the table size observed at the moment of table
ioremap() and use the cache value. This, however, does not help drivers
that peek at the PCIE_MSIX_FLAGS register directly.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>

drivers/pci/msi/msi.c

@@ -632,7 +632,7 @@ static int msix_capability_init(struct pci_dev *dev, struct msix_entry *entries,
 
 	pci_read_config_word(dev, dev->msix_cap + PCI_MSIX_FLAGS, &control);
 	/* Request & Map MSI-X table region */
-	tsize = msix_table_size(control);
+	tsize = pci_msix_vec_count(dev);
 	base = msix_map_region(dev, tsize);
 	if (!base) {
 		ret = -ENOMEM;
@@ -791,8 +791,13 @@ int pci_msix_vec_count(struct pci_dev *dev)
 	if (!dev->msix_cap)
 		return -EINVAL;
 
+	if (dev->flags_qsize)
+		return dev->flags_qsize;
+
 	pci_read_config_word(dev, dev->msix_cap + PCI_MSIX_FLAGS, &control);
-	return msix_table_size(control);
+	dev->flags_qsize = msix_table_size(control);
+
+	return dev->flags_qsize;
 }
 EXPORT_SYMBOL(pci_msix_vec_count);
 

include/linux/pci.h

@@ -351,6 +351,7 @@ struct pci_dev {
 	u8		rom_base_reg;	/* Config register controlling ROM */
 	u8		pin;		/* Interrupt pin this device uses */
 	u16		pcie_flags_reg;	/* Cached PCIe Capabilities Register */
+	u16		flags_qsize;	/* Cached MSIX table size */
 	unsigned long	*dma_alias_mask;/* Mask of enabled devfn aliases */
 
 	struct pci_driver *driver;	/* Driver bound to this device */