iwlwifi: pcie: make cfg vs. trans_cfg more robust

If we (for example) have a trans_cfg entry in the PCI IDs table,
but then don't find a full cfg entry for it in the info table,
we fall through to the code that treats the PCI ID table entry
as a full cfg entry. This obviously causes crashes later, e.g.
when trying to build the firmware name string.

Avoid such crashes by using the low bit of the pointer as a tag
for trans_cfg entries (automatically using a macro that checks
the type when assigning) and then checking that before trying to
use the data as a full entry - if it's just a partial entry at
that point, fail.

Since we're adding some macro magic, also check that the type is
in fact either struct iwl_cfg_trans_params or struct iwl_cfg,
failing compilation ("initializer element is not constant") if
it isn't.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20210330162204.6f69fe6e4128.I921d4ae20ef5276716baeeeda0b001cf25b9b968@changeidSigned-off-by: Luca Coelho <luciano.coelho@intel.com>

drivers/net/wireless/intel/iwlwifi/pcie/drv.c

@@ -17,10 +17,20 @@
 #include "iwl-prph.h"
 #include "internal.h"
 
+#define TRANS_CFG_MARKER BIT(0)
+#define _IS_A(cfg, _struct) __builtin_types_compatible_p(typeof(cfg),	\
+							 struct _struct)
+extern int _invalid_type;
+#define _TRANS_CFG_MARKER(cfg)						\
+	(__builtin_choose_expr(_IS_A(cfg, iwl_cfg_trans_params),	\
+			       TRANS_CFG_MARKER,			\
+	 __builtin_choose_expr(_IS_A(cfg, iwl_cfg), 0, _invalid_type)))
+#define _ASSIGN_CFG(cfg) (_TRANS_CFG_MARKER(cfg) + (kernel_ulong_t)&(cfg))
+
 #define IWL_PCI_DEVICE(dev, subdev, cfg) \
 	.vendor = PCI_VENDOR_ID_INTEL,  .device = (dev), \
 	.subvendor = PCI_ANY_ID, .subdevice = (subdev), \
-	.driver_data = (kernel_ulong_t)&(cfg)
+	.driver_data = _ASSIGN_CFG(cfg)
 
 /* Hardware specific file defines the PCI IDs table for that hardware module */
 static const struct pci_device_id iwl_hw_card_ids[] = {
@@ -1099,19 +1109,22 @@ static const struct iwl_dev_info iwl_dev_info_table[] = {
 
 static int iwl_pci_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
 {
-	const struct iwl_cfg_trans_params *trans =
-		(struct iwl_cfg_trans_params *)(ent->driver_data);
+	const struct iwl_cfg_trans_params *trans;
 	const struct iwl_cfg *cfg_7265d __maybe_unused = NULL;
 	struct iwl_trans *iwl_trans;
 	struct iwl_trans_pcie *trans_pcie;
 	int i, ret;
+	const struct iwl_cfg *cfg;
+
+	trans = (void *)(ent->driver_data & ~TRANS_CFG_MARKER);
+
 	/*
 	 * This is needed for backwards compatibility with the old
 	 * tables, so we don't need to change all the config structs
 	 * at the same time.  The cfg is used to compare with the old
 	 * full cfg structs.
 	 */
-	const struct iwl_cfg *cfg = (struct iwl_cfg *)(ent->driver_data);
+	cfg = (void *)(ent->driver_data & ~TRANS_CFG_MARKER);
 
 	/* make sure trans is the first element in iwl_cfg */
 	BUILD_BUG_ON(offsetof(struct iwl_cfg, trans));
@@ -1226,11 +1239,19 @@ static int iwl_pci_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
 
 #endif
 	/*
-	 * If we didn't set the cfg yet, assume the trans is actually
-	 * a full cfg from the old tables.
+	 * If we didn't set the cfg yet, the PCI ID table entry should have
+	 * been a full config - if yes, use it, otherwise fail.
 	 */
-	if (!iwl_trans->cfg)
+	if (!iwl_trans->cfg) {
+		if (ent->driver_data & TRANS_CFG_MARKER) {
+			pr_err("No config found for PCI dev %04x/%04x, rev=0x%x, rfid=0x%x\n",
+			       pdev->device, pdev->subsystem_device,
+			       iwl_trans->hw_rev, iwl_trans->hw_rf_id);
+			ret = -EINVAL;
+			goto out_free_trans;
+		}
 		iwl_trans->cfg = cfg;
+	}
 
 	/* if we don't have a name yet, copy name from the old cfg */
 	if (!iwl_trans->name)