[PATCH v3 2/2] PCI: pciehp: Abort hot-plug if pci_hp_add_bridge() fails

Nam Cao
2024-05-13T14:57:21Z

If a bridge is hot-added without any bus number available for its
downstream bus, pci_hp_add_bridge() will fail. However, the driver
proceeds regardless, and the kernel crashes.

This crash can be reproduced with the QEMU command:
qemu-system-x86_64 -machine pc-q35-2.10 \
-kernel bzImage \
-drive "file=img,format=raw" \
-m 2048 -smp 2 -enable-kvm \
-append "console=ttyS0 root=/dev/sda" \
-nographic \
-device pcie-root-port,bus=pcie.0,id=rp1,slot=1,bus-reserve=0

then hot-plug a bridge at runtime with the QEMU command:
device_add pcie-pci-bridge,id=br1,bus=rp1

and the kernel crashes:

pcieport 0000:00:03.0: pciehp: Slot(1): Button press: will power on in 5 sec
pcieport 0000:00:03.0: pciehp: Slot(1): Card present
pcieport 0000:00:03.0: pciehp: Slot(1): Link Up
pci 0000:01:00.0: [1b36:000e] type 01 class 0x060400 PCIe to PCI/PCI-X bridge
pci 0000:01:00.0: BAR 0 [mem 0x00000000-0x000000ff 64bit]
pci 0000:01:00.0: PCI bridge to [bus 00]
pci 0000:01:00.0: bridge window [io 0x0000-0x0fff]
pci 0000:01:00.0: bridge window [mem 0x00000000-0x000fffff]
pci 0000:01:00.0: bridge window [mem 0x00000000-0x000fffff 64bit pref]
pci 0000:01:00.0: No bus number available for hot-added bridge

(note: kernel should abort hot-plugging right here)

pci 0000:01:00.0: BAR 0 [mem 0xfe800000-0xfe8000ff 64bit]: assigned
pcieport 0000:00:03.0: PCI bridge to [bus 01]
pcieport 0000:00:03.0: bridge window [io 0x1000-0x1fff]
pcieport 0000:00:03.0: bridge window [mem 0xfe800000-0xfe9fffff]
pcieport 0000:00:03.0: bridge window [mem 0xfe000000-0xfe1fffff 64bit pref]
shpchp 0000:01:00.0: HPC vendor_id 1b36 device_id e ss_vid 0 ss_did 0
shpchp 0000:01:00.0: enabling device (0000 -> 0002)
BUG: kernel NULL pointer dereference, address: 00000000000000da
PGD 0 P4D 0
Oops: 0002 [#1] PREEMPT SMP NOPTI
CPU: 0 PID: 46 Comm: irq/24-pciehp Not tainted 6.9.0-rc1-00001-g2e0239d47d75 #33
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:shpc_init+0x3fb/0x9d0
[stack dump and register dump cut out]

Fix this by aborting the hot-plug if pci_hp_add_bridge() fails.

Fixes: 0eb3bcfd088e ("[PATCH] pciehp: allow bridged card hotplug")
Signed-off-by: Nam Cao <namcao@linutronix.de>
Cc: <stable@vger.kernel.org>
---
v3: revert back to the solution in v1 (calling
pci_stop_and_remove_bus_device() and returning negative error code)

v2:
- remove "Cc: Rajesh Shah <rajesh.shah@intel.com>" (this address bounce)
- add more information to commit message
- return 0 instead of -EINVAL

drivers/pci/hotplug/pciehp_pci.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/hotplug/pciehp_pci.c b/drivers/pci/hotplug/pciehp_pci.c
index ad12515a4a12..de783d7c8a16 100644
--- a/drivers/pci/hotplug/pciehp_pci.c
+++ b/drivers/pci/hotplug/pciehp_pci.c
@@ -59,7 +59,11 @@ int pciehp_configure_device(struct controller *ctrl)
}

for_each_pci_bridge(dev, parent)
- pci_hp_add_bridge(dev);
+ if (pci_hp_add_bridge(dev)) {
+ pci_stop_and_remove_bus_device(dev);
+ ret = -EINVAL;
+ goto out;
+ }

pci_assign_unassigned_bridge_resources(bridge);
pcie_bus_configure_settings(parent);
--
2.39.2