Introduce a PCI parameter that disables the automatic attachment of
untrusted devices to their drivers.
Signed-off-by: Rajat Jain <rajatja@xxxxxxxxxx>
---
Context:
I set out to implement the approach outlined in
https://lkml.org/lkml/2020/6/9/1331
https://lkml.org/lkml/2020/6/15/1453
But to my surprise, I found that the new hotplugged PCI devices
were getting automatically attached to drivers even though
/sys/bus/pci/drivers_autoprobe was set to 0.
I realized that the device core's "drivers_autoprobe":
* only disables the *initial* probe of the device (i.e. from
device_add()). If a subsystem calls device_attach() explicitly
for its devices like PCI subsystem does, the drivers_autoprobe
setting does not matter. The core will attach device to the driver.
This looks like correct semantic behavior to me because PCI is
explicitly calling device_attach(), which is a way to explicitly
ask the core to find and attach a driver for a device.
* "drivers_autoprobe" cannot be controlled at boot time (to restrict
any drivers before userspace comes up).
The options I considered were:
1) Change device_attach() so that it takes into consideration the
drivers_autoprobe property. Not sure if this is semantically correct
thing to do though. If I do this, then the only way a driver can
be attached to the drivers would be via userspace
(/sys/bus/pci/drivers/bind) (Good for our use case though!).
2) Make the drivers_autoprobe property available to PCI to use
(currently it is private to device core). The PCI could use this
to determine whether or not to call device_attach(). This still
leaves the other problem (of not being able to set
drivers_autoprobe via command line open).
3) I found the pci_dev->match_driver, which seemed similar to what I
am trying to do, but can't be controlled from userspace. I considered
populating that field based on drivers_autoprobe (still need (2)).
But the problem is that there is the AMD IOMMU driver which is setting
this independently, so setting the match_driver based on
drivers_autoprobe may not be a good idea. May be we can populate it
for untrusted devicesi, based on the parameter that I'm introducing?
4) This patch was my option 4 that helps fix both the problems for me.
drivers/pci/bus.c | 11 ++++++++---
drivers/pci/pci.c | 9 +++++++++
drivers/pci/pci.h | 1 +
3 files changed, 18 insertions(+), 3 deletions(-)
diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
index 3cef835b375fd..336aeeb4c4ebf 100644
--- a/drivers/pci/bus.c
+++ b/drivers/pci/bus.c
@@ -321,9 +321,14 @@ void pci_bus_add_device(struct pci_dev *dev)
pci_bridge_d3_update(dev);
dev->match_driver = true;
- retval = device_attach(&dev->dev);
- if (retval < 0 && retval != -EPROBE_DEFER)
- pci_warn(dev, "device attach failed (%d)\n", retval);
+
+ if (dev->untrusted && pci_dont_attach_untrusted_devs) {
+ pci_info(dev, "not attaching untrusted device\n");
+ } else {
+ retval = device_attach(&dev->dev);
+ if (retval < 0 && retval != -EPROBE_DEFER)
+ pci_warn(dev, "device attach failed (%d)\n", retval);
+ }
pci_dev_assign_added(dev, true);
}
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index ce096272f52b1..dec1f9ef27d71 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -127,6 +127,13 @@ static bool pcie_ats_disabled;
/* If set, the PCI config space of each device is printed during boot. */
bool pci_early_dump;
+/*
+ * If set, the devices with "untrusted" flag shall not be attached automatically
+ * Userspace will need to attach them manually:
+ * echo <pci device> > /sys/bus/pci/drivers/<driver>/bind
+ */
+bool pci_dont_attach_untrusted_devs;
+
bool pci_ats_disabled(void)
{
return pcie_ats_disabled;
@@ -6522,6 +6529,8 @@ static int __init pci_setup(char *str)
pci_add_flags(PCI_SCAN_ALL_PCIE_DEVS);
} else if (!strncmp(str, "disable_acs_redir=", 18)) {
disable_acs_redir_param = str + 18;
+ } else if (!strcmp(str, "dont_attach_untrusted_devs")) {
+ pci_dont_attach_untrusted_devs = true;
} else {
pr_err("PCI: Unknown option `%s'\n", str);
}
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 6d3f758671064..30ffad047d926 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -13,6 +13,7 @@
extern const unsigned char pcie_link_speed[];
extern bool pci_early_dump;
+extern bool pci_dont_attach_untrusted_devs;
bool pcie_cap_has_lnkctl(const struct pci_dev *dev);
bool pcie_cap_has_rtctl(const struct pci_dev *dev);
--
2.27.0.212.ge8ba1cc988-goog
