[PATCH v4 16/19] PCI: liveupdate: Add feature header to struct pci_dev_ser

[Tarun Sahu <tarunsahu@google.com>]

Precede each serialized PCI device entry in the PCI Live Update KHO block
set with struct kho_ser_hdr via DECLARE_KHO_SER so future per-device PCI
Live Update features can append fields to struct pci_dev_ser without
breaking compatibility between adjacent kernels.

Mark struct pci_dev_ser as 8-byte aligned since its largest member is u32,
initialize the device block sets with kho_ser_size(pci_dev_ser),
initialize each entry feature header in pci_flb_alloc_dev_ser(), and
validate incoming device feature headers in pci_flb_retrieve() before
accessing the struct pci_dev_ser payload.

Signed-off-by: Tarun Sahu <tarunsahu@google.com>
---
 drivers/pci/liveupdate.c    | 27 +++++++++++++++++++--------
 include/linux/kho/abi/pci.h |  9 ++++++---
 2 files changed, 25 insertions(+), 11 deletions(-)

diff --git a/drivers/pci/liveupdate.c b/drivers/pci/liveupdate.c
index 0bda94f4a7e4..f4c84bcc0629 100644
--- a/drivers/pci/liveupdate.c
+++ b/drivers/pci/liveupdate.c
@@ -288,7 +288,7 @@ static int pci_flb_preserve(struct liveupdate_flb_op_args *args)
 	ser->devices = 0;
 
 	outgoing->fhdr = fhdr;
-	kho_block_set_init(&outgoing->block_set, sizeof(struct pci_dev_ser));
+	kho_block_set_init(&outgoing->block_set, kho_ser_size(pci_dev_ser));
 
 	args->obj = no_free_ptr(outgoing);
 	args->data = virt_to_phys(fhdr);
@@ -318,6 +318,7 @@ static int pci_flb_retrieve(struct liveupdate_flb_op_args *args)
 {
 	DECLARE_KHO_SER_HDR(pci_ser, *fhdr) = phys_to_virt(args->data);
 	struct pci_flb_incoming *incoming;
+	DECLARE_KHO_SER_HDR(pci_dev_ser, *dev_fhdr);
 	struct pci_dev_ser *dev_ser;
 	struct kho_block_set_it it;
 	struct pci_ser *ser;
@@ -338,15 +339,20 @@ static int pci_flb_retrieve(struct liveupdate_flb_op_args *args)
 	incoming->fhdr = fhdr;
 	xa_init(&incoming->xa);
 
-	kho_block_set_init(&incoming->block_set, sizeof(struct pci_dev_ser));
+	kho_block_set_init(&incoming->block_set, kho_ser_size(pci_dev_ser));
 	ret = kho_block_set_restore(&incoming->block_set, ser->devices);
 	if (ret)
 		panic("Failed to restore devices KHO block set (%d)\n", ret);
 
 	kho_block_set_it_init(&it, &incoming->block_set);
-	while ((dev_ser = kho_block_set_it_read_entry(&it))) {
+	while ((dev_fhdr = kho_block_set_it_read_entry(&it))) {
 		unsigned long key;
 
+		ret = kho_ser_validate(dev_fhdr, pci_dev_ser);
+		if (ret)
+			panic("Failed to validate incoming PCI device feature header (%d)\n", ret);
+
+		dev_ser = kho_ser_payload(dev_fhdr, pci_dev_ser);
 		if (!dev_ser->refcount)
 			continue;
 
@@ -456,6 +462,7 @@ static struct pci_flb_outgoing *pci_liveupdate_flb_get_outgoing(void)
 
 static struct pci_dev_ser *pci_flb_alloc_dev_ser(struct pci_flb_outgoing *outgoing)
 {
+	DECLARE_KHO_SER_HDR(pci_dev_ser, *fhdr);
 	struct pci_dev_ser *dev_ser;
 	struct kho_block_set_it it;
 	u64 count = 0;
@@ -464,9 +471,12 @@ static struct pci_dev_ser *pci_flb_alloc_dev_ser(struct pci_flb_outgoing *outgoi
 	kho_block_set_it_init(&it, &outgoing->block_set);
 
 	/* Try to find an existing, previously unpreserved, entry. */
-	while ((dev_ser = kho_block_set_it_read_entry(&it))) {
-		if (!dev_ser->refcount)
+	while ((fhdr = kho_block_set_it_read_entry(&it))) {
+		dev_ser = kho_ser_payload(fhdr, pci_dev_ser);
+		if (!dev_ser->refcount) {
+			kho_ser_init(fhdr, pci_dev_ser);
 			return dev_ser;
+		}
 
 		count++;
 	}
@@ -480,11 +490,12 @@ static struct pci_dev_ser *pci_flb_alloc_dev_ser(struct pci_flb_outgoing *outgoi
 		kho_block_set_it_init(&it, &outgoing->block_set);
 
 	/* This should always succeed since kho_block_set_grow() succeeded. */
-	dev_ser = kho_block_set_it_reserve_entry(&it);
-	if (WARN_ON_ONCE(!dev_ser))
+	fhdr = kho_block_set_it_reserve_entry(&it);
+	if (WARN_ON_ONCE(!fhdr))
 		return ERR_PTR(-ENOSPC);
 
-	return dev_ser;
+	kho_ser_init(fhdr, pci_dev_ser);
+	return kho_ser_payload(fhdr, pci_dev_ser);
 }
 
 static int pci_liveupdate_unpreserve_device(struct pci_flb_outgoing *outgoing,
diff --git a/include/linux/kho/abi/pci.h b/include/linux/kho/abi/pci.h
index f53f6350e53d..77ddf5938822 100644
--- a/include/linux/kho/abi/pci.h
+++ b/include/linux/kho/abi/pci.h
@@ -19,7 +19,8 @@
  * File-Lifecycle Bound (FLB) data, identified by the compatible string
  * ``"pci-v2"`` and laid out as described by the structs below.
  *
- * struct pci_ser is preceded by &struct kho_ser_hdr, which records the
+ * Both &struct pci_ser and each &struct pci_dev_ser entry are preceded by
+ * &struct kho_ser_hdr, which records the
  * total size of the serialization and feature flags. See
  * include/linux/kho/abi/feature.h for the feature header layout, feature
  * rules, and validation.
@@ -42,14 +43,16 @@
  *            reference count is equal to the number of preserved devices at or
  *            below it in the PCI hierarchy when the struct pci_dev_ser is in
  *            use, and 0 otherwise.
+ *
+ * Preceded by &struct kho_ser_hdr.
  */
 struct pci_dev_ser {
 	u32 domain;
 	u16 bdf;
 	u16 refcount;
-};
+} __aligned(8);
 
-static_assert(sizeof(struct pci_dev_ser) == 8);
+DECLARE_KHO_SER(pci_dev_ser, 8, 0, 0);
 
 /**
  * struct pci_ser - PCI Subsystem Live Update State
-- 
2.56.0.506.g506a7eabc5-goog