linux-kernel - [PATCH 1/2] PCI/MSI: Cache the MSIX table size

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Message-Id: <20230119170633.40944-2-alexander.shishkin@linux.intel.com>
Date:   Thu, 19 Jan 2023 19:06:32 +0200
From:   Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>, linux-pci@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Marc Zyngier <maz@...nel.org>,
        darwi@...utronix.de, elena.reshetova@...el.com,
        kirill.shutemov@...ux.intel.com,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        stable@...r.kernel.org
Subject: [PATCH 1/2] 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 kernel page fault in
pci_write_msg_msix().

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

Signed-off-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Reviewed-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc: stable@...r.kernel.org
---
 drivers/pci/msi/api.c | 7 ++++++-
 drivers/pci/msi/msi.c | 2 +-
 include/linux/pci.h   | 1 +
 3 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/msi/api.c b/drivers/pci/msi/api.c
index b8009aa11f3c..617ea1256487 100644
--- a/drivers/pci/msi/api.c
+++ b/drivers/pci/msi/api.c
@@ -75,8 +75,13 @@ 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);
 
diff --git a/drivers/pci/msi/msi.c b/drivers/pci/msi/msi.c
index 1f716624ca56..d50cd45119f1 100644
--- a/drivers/pci/msi/msi.c
+++ b/drivers/pci/msi/msi.c
@@ -715,7 +715,7 @@ 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);
 	dev->msix_base = msix_map_region(dev, tsize);
 	if (!dev->msix_base) {
 		ret = -ENOMEM;
diff --git a/include/linux/pci.h b/include/linux/pci.h
index adffd65e84b4..2e1a72a2139d 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -352,6 +352,7 @@ 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 */
-- 
2.39.0