[PATCH] PCI: host-generic: Fix NULL pointer dereference on 32-bit CAM systems

[Steffen Persvold]

On 32-bit systems the config space is too large to ioremap in one go, so
pci_ecam_create() maps each bus segment separately and relies on the
->add_bus callback (pci_ecam_add_bus) to populate the per-bus mapping in
cfg->winp[]. pci_ecam_map_bus() then uses that mapping as the base for
every config access.

The generic ECAM ops (pci_generic_ecam_ops) already provide the ->add_bus
and ->remove_bus callbacks, but the CAM (legacy) ops in pci-host-generic.c
do not. As a result, on a 32-bit host using "pci-host-cam-generic" the
per-bus mapping is never set up and the first config read dereferences a
NULL base, crashing during bus enumeration:

[    1.430647] Unable to handle kernel NULL pointer dereference at virtual address 00000800
[    1.439441] Oops [#1]
[    1.442152] CPU: 0 PID: 1 Comm: swapper Not tainted 6.9.7+ #43
[    1.448753] Hardware name: Digilent Nexys-Video-A7 RV32 (DT)
[    1.454968] epc : pci_generic_config_read+0x40/0xb0
[    1.460652]  ra : pci_generic_config_read+0x2c/0xb0
[    1.534729] [<c038db9c>] pci_generic_config_read+0x40/0xb0
[    1.541096] [<c038da04>] pci_bus_read_config_dword+0x50/0xb0
[    1.547623] [<c0391e94>] pci_bus_generic_read_dev_vendor_id+0x3c/0x1ec
[    1.555010] [<c039245c>] pci_scan_single_device+0xa4/0x11c
[    1.561273] [<c0392570>] pci_scan_slot+0x9c/0x23c
[    1.566716] [<c039388c>] pci_scan_child_bus_extend+0x58/0x2f4
[    1.573275] [<c0393db0>] pci_scan_root_bus_bridge+0x64/0xe8
[    1.579650] [<c0393e54>] pci_host_probe+0x20/0xc8
[    1.591396] [<c03bc6f4>] pci_host_common_probe+0x144/0x1e4

Fix this by giving the CAM ops the same ->add_bus/->remove_bus callbacks.
Since pci_ecam_add_bus() and pci_ecam_remove_bus() are static to ecam.c,
move the CAM ops definition there as pci_generic_cam_ops (mirroring
pci_generic_ecam_ops) and export it for pci-host-generic.c to reference.

Fixes: 8fe55ef23387 ("PCI: Dynamically map ECAM regions")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Steffen Persvold <spersvold@xxxxxxxxx>
---
 drivers/pci/controller/pci-host-generic.c | 11 +----------
 drivers/pci/ecam.c                        | 13 +++++++++++++
 include/linux/pci-ecam.h                  |  3 +++
 3 files changed, 17 insertions(+), 10 deletions(-)

diff --git a/drivers/pci/controller/pci-host-generic.c b/drivers/pci/controller/pci-host-generic.c
index c1bc0d34..9e85c6e9 100644
--- a/drivers/pci/controller/pci-host-generic.c
+++ b/drivers/pci/controller/pci-host-generic.c
@@ -16,15 +16,6 @@
 
 #include "pci-host-common.h"
 
-static const struct pci_ecam_ops gen_pci_cfg_cam_bus_ops = {
-	.bus_shift	= 16,
-	.pci_ops	= {
-		.map_bus	= pci_ecam_map_bus,
-		.read		= pci_generic_config_read,
-		.write		= pci_generic_config_write,
-	}
-};
-
 static bool pci_dw_valid_device(struct pci_bus *bus, unsigned int devfn)
 {
 	struct pci_config_window *cfg = bus->sysdata;
@@ -60,7 +51,7 @@ static const struct pci_ecam_ops pci_dw_ecam_bus_ops = {
 
 static const struct of_device_id gen_pci_of_match[] = {
 	{ .compatible = "pci-host-cam-generic",
-	  .data = &gen_pci_cfg_cam_bus_ops },
+	  .data = &pci_generic_cam_ops },
 
 	{ .compatible = "pci-host-ecam-generic",
 	  .data = &pci_generic_ecam_ops },
diff --git a/drivers/pci/ecam.c b/drivers/pci/ecam.c
index 119de32f..a9b3bce2 100644
--- a/drivers/pci/ecam.c
+++ b/drivers/pci/ecam.c
@@ -208,6 +208,19 @@ const struct pci_ecam_ops pci_generic_ecam_ops = {
 };
 EXPORT_SYMBOL_GPL(pci_generic_ecam_ops);
 
+/* CAM ops */
+const struct pci_ecam_ops pci_generic_cam_ops = {
+	.bus_shift	= 16,
+	.pci_ops	= {
+		.add_bus	= pci_ecam_add_bus,
+		.remove_bus	= pci_ecam_remove_bus,
+		.map_bus	= pci_ecam_map_bus,
+		.read		= pci_generic_config_read,
+		.write		= pci_generic_config_write,
+	}
+};
+EXPORT_SYMBOL_GPL(pci_generic_cam_ops);
+
 #if defined(CONFIG_ACPI) && defined(CONFIG_PCI_QUIRKS)
 /* ECAM ops for 32-bit access only (non-compliant) */
 const struct pci_ecam_ops pci_32b_ops = {
diff --git a/include/linux/pci-ecam.h b/include/linux/pci-ecam.h
index d9306514..044f67ce 100644
--- a/include/linux/pci-ecam.h
+++ b/include/linux/pci-ecam.h
@@ -81,6 +81,9 @@ void __iomem *pci_ecam_map_bus(struct pci_bus *bus, unsigned int devfn,
 /* default ECAM ops */
 extern const struct pci_ecam_ops pci_generic_ecam_ops;
 
+/* default CAM ops */
+extern const struct pci_ecam_ops pci_generic_cam_ops;
+
 #if defined(CONFIG_ACPI) && defined(CONFIG_PCI_QUIRKS)
 extern const struct pci_ecam_ops pci_32b_ops;	/* 32-bit accesses only */
 extern const struct pci_ecam_ops pci_32b_read_ops; /* 32-bit read only */

base-commit: 53bf92818a8362815708fc7b18e6d2c6a5fc665b
-- 
2.40.1