[RFC,v2,08/20] PCI/CMA: Reauthenticate devices on reset and resume

Commit Message

Alistair Francis Feb. 27, 2025, 3:09 a.m. UTC

From: Lukas Wunner <[e-mail]>

CMA-SPDM state is lost when a device undergoes a Conventional Reset.
(But not a Function Level Reset, PCIe r6.2 sec 6.6.2.)  A D3cold to D0
transition implies a Conventional Reset (PCIe r6.2 sec 5.8).

Thus, reauthenticate devices on resume from D3cold and on recovery from
a Secondary Bus Reset or DPC-induced Hot Reset.

The requirement to reauthenticate devices on resume from system sleep
(and in the future reestablish IDE encryption) is the reason why SPDM
needs to be in-kernel:  During ->resume_noirq, which is the first phase
after system sleep, the PCI core walks down the hierarchy, puts each
device in D0, restores its config space and invokes the driver's
->resume_noirq callback.  The driver is afforded the right to access the
device already during this phase.

To retain this usage model in the face of authentication and encryption,
CMA-SPDM reauthentication and IDE reestablishment must happen during the
->resume_noirq phase, before the driver's first access to the device.
The driver is thus afforded seamless authenticated and encrypted access
until the last moment before suspend and from the first moment after
resume.

During the ->resume_noirq phase, device interrupts are not yet enabled.
It is thus impossible to defer CMA-SPDM reauthentication to a user space
component on an attached disk or on the network, making an in-kernel
SPDM implementation mandatory.

The same catch-22 exists on recovery from a Conventional Reset:  A user
space SPDM implementation might live on a device which underwent reset,
rendering its execution impossible.

Signed-off-by: Lukas Wunner <[e-mail]>
Reviewed-by: Alistair Francis <[e-mail]>
---
 drivers/pci/cma.c        | 15 +++++++++++++++
 drivers/pci/pci-driver.c |  1 +
 drivers/pci/pci.c        | 12 ++++++++++--
 drivers/pci/pci.h        |  2 ++
 drivers/pci/pcie/err.c   |  3 +++
 5 files changed, 31 insertions(+), 2 deletions(-)

Patch

diff --git a/drivers/pci/cma.c b/drivers/pci/cma.c
index e974d489c7a2..f2c435b04b92 100644
--- a/drivers/pci/cma.c
+++ b/drivers/pci/cma.c
@@ -195,6 +195,21 @@  void pci_cma_init(struct pci_dev *pdev)
 	spdm_authenticate(pdev->spdm_state);
 }
 
+/**
+ * pci_cma_reauthenticate() - Perform CMA-SPDM authentication again
+ * @pdev: Device to reauthenticate
+ *
+ * Can be called by drivers after device identity has mutated,
+ * e.g. after downloading firmware to an FPGA device.
+ */
+void pci_cma_reauthenticate(struct pci_dev *pdev)
+{
+	if (!pdev->spdm_state)
+		return;
+
+	spdm_authenticate(pdev->spdm_state);
+}
+
 void pci_cma_destroy(struct pci_dev *pdev)
 {
 	if (!pdev->spdm_state)
diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
index f57ea36d125d..6dd24ae2d1ee 100644
--- a/drivers/pci/pci-driver.c
+++ b/drivers/pci/pci-driver.c
@@ -566,6 +566,7 @@  static void pci_pm_default_resume_early(struct pci_dev *pci_dev)
 	pci_pm_power_up_and_verify_state(pci_dev);
 	pci_restore_state(pci_dev);
 	pci_pme_restore(pci_dev);
+	pci_cma_reauthenticate(pci_dev);
 }
 
 static void pci_pm_bridge_power_up_actions(struct pci_dev *pci_dev)
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 869d204a70a3..b462bab597f7 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -5074,8 +5074,16 @@  static int pci_reset_bus_function(struct pci_dev *dev, bool probe)
 
 	rc = pci_dev_reset_slot_function(dev, probe);
 	if (rc != -ENOTTY)
-		return rc;
-	return pci_parent_bus_reset(dev, probe);
+		goto done;
+
+	rc = pci_parent_bus_reset(dev, probe);
+
+done:
+	/* CMA-SPDM state is lost upon a Conventional Reset */
+	if (!probe)
+		pci_cma_reauthenticate(dev);
+
+	return rc;
 }
 
 static int cxl_reset_bus_function(struct pci_dev *dev, bool probe)
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 69ba2ae9a0cd..fa6e3ae10b67 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -451,9 +451,11 @@  static inline void pci_doe_disconnected(struct pci_dev *pdev) { }
 #ifdef CONFIG_PCI_CMA
 void pci_cma_init(struct pci_dev *pdev);
 void pci_cma_destroy(struct pci_dev *pdev);
+void pci_cma_reauthenticate(struct pci_dev *pdev);
 #else
 static inline void pci_cma_init(struct pci_dev *pdev) { }
 static inline void pci_cma_destroy(struct pci_dev *pdev) { }
+static inline void pci_cma_reauthenticate(struct pci_dev *pdev) { }
 #endif
 
 #ifdef CONFIG_PCI_NPEM
diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
index 31090770fffc..0028582f0590 100644
--- a/drivers/pci/pcie/err.c
+++ b/drivers/pci/pcie/err.c
@@ -133,6 +133,9 @@  static int report_slot_reset(struct pci_dev *dev, void *data)
 	pci_ers_result_t vote, *result = data;
 	const struct pci_error_handlers *err_handler;
 
+	/* CMA-SPDM state is lost upon a Conventional Reset */
+	pci_cma_reauthenticate(dev);
+
 	device_lock(&dev->dev);
 	pdrv = dev->driver;
 	if (!pdrv || !pdrv->err_handler || !pdrv->err_handler->slot_reset)