PCI: Allow drivers to request exclusive config regions

PCI config space access from user space has traditionally been
unrestricted with writes being an understood risk for device operation.

Unfortunately, device breakage or odd behavior from config writes lacks
indicators that can leave driver writers confused when evaluating
failures.  This is especially true with the new PCIe Data Object
Exchange (DOE) mailbox protocol where backdoor shenanigans from user
space through things such as vendor defined protocols may affect device
operation without complete breakage.

A prior proposal restricted read and writes completely.[1]  Greg and
Bjorn pointed out that proposal is flawed for a couple of reasons.
First, lspci should always be allowed and should not interfere with any
device operation.  Second, setpci is a valuable tool that is sometimes
necessary and it should not be completely restricted.[2]  Finally
methods exist for full lock of device access if required.

Even though access should not be restricted it would be nice for driver
writers to be able to flag critical parts of the config space such that
interference from user space can be detected.

Introduce pci_request_config_region_exclusive() to mark exclusive config
regions.  Such regions trigger a warning and kernel taint if accessed
via user space.

Create pci_warn_once() to restrict the user from spamming the log.

[1] https://lore.kernel.org/all/161663543465.1867664.5674061943008380442.stgit@dwillia2-desk3.amr.corp.intel.com/
[2] https://lore.kernel.org/all/YF8NGeGv9vYcMfTV@kroah.com/

Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Suggested-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://lore.kernel.org/r/20220926215711.2893286-2-ira.weiny@intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 17 insertions, 0 deletions

diff --git a/include/linux/pci.h b/include/linux/pci.h
index 2bda4a4e47e8..575849a100a3 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -409,6 +409,7 @@ struct pci_dev {
 	 */
 	unsigned int	irq;
 	struct resource resource[DEVICE_COUNT_RESOURCE]; /* I/O and memory regions + expansion ROMs */
+	struct resource driver_exclusive_resource;	 /* driver exclusive resource ranges */
 
 	bool		match_driver;		/* Skip attaching driver */
 
@@ -1407,6 +1408,21 @@ int pci_request_selected_regions(struct pci_dev *, int, const char *);
 int pci_request_selected_regions_exclusive(struct pci_dev *, int, const char *);
 void pci_release_selected_regions(struct pci_dev *, int);
 
+static inline __must_check struct resource *
+pci_request_config_region_exclusive(struct pci_dev *pdev, unsigned int offset,
+				    unsigned int len, const char *name)
+{
+	return __request_region(&pdev->driver_exclusive_resource, offset, len,
+				name, IORESOURCE_EXCLUSIVE);
+}
+
+static inline void pci_release_config_region(struct pci_dev *pdev,
+					     unsigned int offset,
+					     unsigned int len)
+{
+	__release_region(&pdev->driver_exclusive_resource, offset, len);
+}
+
 /* drivers/pci/bus.c */
 void pci_add_resource(struct list_head *resources, struct resource *res);
 void pci_add_resource_offset(struct list_head *resources, struct resource *res,
@@ -2484,6 +2500,7 @@ void pci_uevent_ers(struct pci_dev *pdev, enum  pci_ers_result err_type);
 #define pci_crit(pdev, fmt, arg...)	dev_crit(&(pdev)->dev, fmt, ##arg)
 #define pci_err(pdev, fmt, arg...)	dev_err(&(pdev)->dev, fmt, ##arg)
 #define pci_warn(pdev, fmt, arg...)	dev_warn(&(pdev)->dev, fmt, ##arg)
+#define pci_warn_once(pdev, fmt, arg...) dev_warn_once(&(pdev)->dev, fmt, ##arg)
 #define pci_notice(pdev, fmt, arg...)	dev_notice(&(pdev)->dev, fmt, ##arg)
 #define pci_info(pdev, fmt, arg...)	dev_info(&(pdev)->dev, fmt, ##arg)
 #define pci_dbg(pdev, fmt, arg...)	dev_dbg(&(pdev)->dev, fmt, ##arg)