cpu/x86/smm: Add PCI resource store functionality

In certain cases data within protected memmory areas like SMRAM could
be leaked or modified if an attacker remaps PCI BARs to point within
that area. Add support to the existing SMM runtime to allow storing
PCI resources in SMRAM and then later retrieving them.

BRANCH=guybrush
BUG=b:186792595
TEST=builds

Signed-off-by: Robert Zieba <robertzieba@google.com>
Change-Id: I23fb1e935dd1b89f1cc5c834cc2025f0fe5fda37
Reviewed-on: https://review.coreboot.org/c/coreboot/+/67931
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Karthik Ramasubramanian <kramasub@google.com>

src/cpu/x86/Kconfig

@@ -168,6 +168,19 @@ config SMM_LAPIC_REMAP_MITIGATION
 		|| NORTHBRIDGE_INTEL_E7505 || NORTHBRIDGE_INTEL_IRONLAKE
 	default n
 
+config SMM_PCI_RESOURCE_STORE
+	bool
+	default n
+	help
+	  This option enables support for storing PCI resources in SMRAM so
+	  SMM can tell if they've been altered.
+
+config SMM_PCI_RESOURCE_STORE_NUM_SLOTS
+	int
+	default 8
+	help
+	  Number of slots available to store PCI BARs in SMRAM
+
 config X86_AMD_FIXED_MTRRS
 	bool
 	default n

src/cpu/x86/smm/Makefile.inc

@@ -1,6 +1,9 @@
 ## SPDX-License-Identifier: GPL-2.0-only
 
 ramstage-y += smm_module_loader.c
+ramstage-$(CONFIG_SMM_PCI_RESOURCE_STORE) += pci_resource_store.c
+
+smm-$(CONFIG_SMM_PCI_RESOURCE_STORE) += pci_resource_store.c
 
 ifeq ($(CONFIG_ARCH_RAMSTAGE_X86_32),y)
 $(eval $(call create_class_compiler,smm,x86_32))

src/cpu/x86/smm/pci_resource_store.c

@@ -0,0 +1,73 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <cpu/x86/smm.h>
+#include <device/device.h>
+#include <device/pci_def.h>
+#include <device/pci_ops.h>
+
+void smm_pci_get_stored_resources(const volatile struct smm_pci_resource_info **out_slots,
+				  size_t *out_size)
+{
+	*out_slots = smm_get_pci_resource_store();
+	*out_size = CONFIG_SMM_PCI_RESOURCE_STORE_NUM_SLOTS;
+}
+
+bool smm_pci_resource_store_fill_resources(struct smm_pci_resource_info *slots, size_t num_slots,
+					   const struct device **devices, size_t num_devices)
+{
+	size_t i_slot = 0;
+
+	for (size_t i_dev = 0; i_dev < num_devices; i_dev++) {
+		if (i_slot >= num_slots) {
+			printk(BIOS_ERR, "Failed to store all PCI resources, number of devices exceeds %zd slots\n",
+			       num_slots);
+			return false;
+		}
+
+		if (!is_pci(devices[i_dev])) {
+			printk(BIOS_WARNING, "Skipping storing PCI resources for device at index %zd, not a PCI device\n",
+			       i_dev);
+			continue;
+		}
+
+		pci_devfn_t pci_addr = PCI_BDF(devices[i_dev]);
+		slots[i_slot].pci_addr = pci_addr;
+		slots[i_slot].class_device = PCI_CLASS_GET_DEVICE(devices[i_dev]->class);
+		slots[i_slot].class_prog = PCI_CLASS_GET_PROG(devices[i_dev]->class);
+
+		/* Use the resource list to get our BARs. */
+		if (!devices[i_dev]->resource_list)
+			continue;
+
+		size_t i_res = 0;
+		for (const struct resource *res = devices[i_dev]->resource_list; res != NULL;
+			res = res->next) {
+			slots[i_slot].resources[i_res] = *res;
+			slots[i_slot].resources[i_res].next = NULL;
+
+			if (i_res > 0)
+				slots[i_slot].resources[i_res - 1].next = (struct resource *)&slots[i_slot].resources[i_res];
+
+			if (++i_res >= SMM_PCI_RESOURCE_STORE_NUM_RESOURCES) {
+				if (res->next)
+					printk(BIOS_WARNING, "Number of PCI resources exceeds supported storage count\n");
+				break;
+			}
+		}
+
+		i_slot++;
+	}
+
+	return true;
+}
+
+void __weak smm_mainboard_pci_resource_store_init(struct smm_pci_resource_info *slots,
+						  size_t size)
+{
+}
+
+void smm_pci_resource_store_init(struct smm_runtime *smm_runtime)
+{
+	smm_mainboard_pci_resource_store_init(&smm_runtime->pci_resources[0],
+					 CONFIG_SMM_PCI_RESOURCE_STORE_NUM_SLOTS);
+}

src/cpu/x86/smm/smm_module_handler.c

@@ -195,6 +195,13 @@ asmlinkage void smm_handler_start(void *arg)
 	southbridge_smi_set_eos();
 }
 
+#if CONFIG(SMM_PCI_RESOURCE_STORE)
+const volatile struct smm_pci_resource_info *smm_get_pci_resource_store(void)
+{
+	return &smm_runtime.pci_resources[0];
+}
+#endif
+
 RMODULE_ENTRY(smm_handler_start);
 
 /* Provide a default implementation for all weak handlers so that relocation

src/cpu/x86/smm/smm_module_loader.c

@@ -343,6 +343,9 @@ static void setup_smihandler_params(struct smm_runtime *mod_params,
 		mod_params->smm_log_level = mainboard_set_smm_log_level();
 	else
 		mod_params->smm_log_level = 0;
+
+	if (CONFIG(SMM_PCI_RESOURCE_STORE))
+		smm_pci_resource_store_init(mod_params);
 }
 
 static void print_region(const char *name, const struct region region)