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>

diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index 0a2eeb82cebde8149c9c9b46bf2d72dfbae132ca..6c250eb214e80f4962c4298e4918507d9a2bc11a 100644 (file)
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -756,6 +756,13 @@ static ssize_t pci_write_config(struct file *filp, struct kobject *kobj,
        if (ret)
                return ret;
 
+       if (resource_is_exclusive(&dev->driver_exclusive_resource, off,
+                                 count)) {
+               pci_warn_once(dev, "%s: Unexpected write to kernel-exclusive config offset %llx",
+                             current->comm, off);
+               add_taint(TAINT_USER, LOCKDEP_STILL_OK);
+       }
+
        if (off > dev->cfg_size)
                return 0;
        if (off + count > dev->cfg_size) {

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index b66fa42c4b1fa21546f60514fcc64107528b4e82..2f4e88a44e8b6762f7f3d88b0623ca4e10c192a9 100644 (file)
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -2307,6 +2307,12 @@ struct pci_dev *pci_alloc_dev(struct pci_bus *bus)
        INIT_LIST_HEAD(&dev->bus_list);
        dev->dev.type = &pci_dev_type;
        dev->bus = pci_bus_get(bus);
+       dev->driver_exclusive_resource = (struct resource) {
+               .name = "PCI Exclusive",
+               .start = 0,
+               .end = -1,
+       };
+
 #ifdef CONFIG_PCI_MSI
        raw_spin_lock_init(&dev->msi_lock);
 #endif

diff --git a/include/linux/ioport.h b/include/linux/ioport.h
index 27642ca15d932f22823ef7b0a003a2d1ca1333f8..4ae3c541ea6f485943552fff034721042257a88a 100644 (file)
--- a/include/linux/ioport.h
+++ b/include/linux/ioport.h
@@ -318,6 +318,8 @@ extern void __devm_release_region(struct device *dev, struct resource *parent,
                                  resource_size_t start, resource_size_t n);
 extern int iomem_map_sanity_check(resource_size_t addr, unsigned long size);
 extern bool iomem_is_exclusive(u64 addr);
+extern bool resource_is_exclusive(struct resource *resource, u64 addr,
+                                 resource_size_t size);
 
 extern int
 walk_system_ram_range(unsigned long start_pfn, unsigned long nr_pages,

diff --git a/include/linux/pci.h b/include/linux/pci.h
index 2bda4a4e47e815d30d68eb52da827c15e0417cde..575849a100a3a2e56aa2f921d6abc755a0d051c2 100644 (file)
--- 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)

diff --git a/kernel/resource.c b/kernel/resource.c
index 4c5e80b92f2f4762471a8ec64371ffb9296773f2..82ed54cd1f0de9560151aa82fb9f30c15e58b1ea 100644 (file)
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -1707,18 +1707,15 @@ static int strict_iomem_checks;
  *
  * Returns true if exclusive to the kernel, otherwise returns false.
  */
-bool iomem_is_exclusive(u64 addr)
+bool resource_is_exclusive(struct resource *root, u64 addr, resource_size_t size)
 {
        const unsigned int exclusive_system_ram = IORESOURCE_SYSTEM_RAM |
                                                  IORESOURCE_EXCLUSIVE;
        bool skip_children = false, err = false;
-       int size = PAGE_SIZE;
        struct resource *p;
 
-       addr = addr & PAGE_MASK;
-
        read_lock(&resource_lock);
-       for_each_resource(&iomem_resource, p, skip_children) {
+       for_each_resource(root, p, skip_children) {
                if (p->start >= addr + size)
                        break;
                if (p->end < addr) {
@@ -1757,6 +1754,12 @@ bool iomem_is_exclusive(u64 addr)
        return err;
 }
 
+bool iomem_is_exclusive(u64 addr)
+{
+       return resource_is_exclusive(&iomem_resource, addr & PAGE_MASK,
+                                    PAGE_SIZE);
+}
+
 struct resource_entry *resource_list_create_entry(struct resource *res,
                                                  size_t extra_size)
 {