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

commit 008cb88edb41f3c7c8e0ed763ff9f26719830984 upstream.

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:

 Unable to handle kernel NULL pointer dereference at virtual address 00000800
 Oops [#1]
 CPU: 0 PID: 1 Comm: swapper Not tainted 6.9.7+ #43
 Hardware name: Digilent Nexys-Video-A7 RV32 (DT)
 epc : pci_generic_config_read+0x40/0xb0
  ra : pci_generic_config_read+0x2c/0xb0
 [<c038db9c>] pci_generic_config_read+0x40/0xb0
 [<c038da04>] pci_bus_read_config_dword+0x50/0xb0
 [<c0391e94>] pci_bus_generic_read_dev_vendor_id+0x3c/0x1ec
 [<c039245c>] pci_scan_single_device+0xa4/0x11c
 [<c0392570>] pci_scan_slot+0x9c/0x23c
 [<c039388c>] pci_scan_child_bus_extend+0x58/0x2f4
 [<c0393db0>] pci_scan_root_bus_bridge+0x64/0xe8
 [<c0393e54>] pci_host_probe+0x20/0xc8
 [<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.

BUG=b/559877410
TEST=presubmit
RELEASE_NOTE=Fixed CVE-2026-80917 in the Linux kernel.

cos-patch: security-moderate
Fixes: 8fe55ef23387 ("PCI: Dynamically map ECAM regions")
Change-Id: Ie0ab65a2f6ea24160f46bb6d4434b138ce77f928
Signed-off-by: Steffen Persvold <spersvold@gmail.com>
[mani: removed timestamp from log]
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260709122446.3151899-1-spersvold@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kernel CVE Triage Automation <cloud-image-kernel-cve-triage-automation@prod.google.com>
Reviewed-on: https://cos-review.googlesource.com/c/third_party/kernel/+/197507
Reviewed-by: Robert Kolchmeyer <rkolchmeyer@google.com>
Reviewed-by: Miri Amarilio <mirilio@google.com>
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>

• drivers/pci/controller/pci-host-generic.c[diff]
• drivers/pci/ecam.c[diff]
• include/linux/pci-ecam.h[diff]