Re: [PATCH] PCI: hv: Fix panic by calling hv_pci_remove_slots() earlier
From: Bjorn Helgaas <helgaas@kernel.org>
Date: 2019-08-02 19:41:01
Also in:
linux-pci, lkml
Hi Dexuan, The subject line only describes the mechanical code change, which is obvious from the patch. It would be better if we could say something about *why* we need this. On Fri, Aug 02, 2019 at 01:32:28AM +0000, Dexuan Cui wrote:
When a slot is removed, the pci_dev must still exist. pci_remove_root_bus() removes and free all the pci_devs, so hv_pci_remove_slots() must be called before pci_remove_root_bus(), otherwise a general protection fault can happen, if the kernel is built
"general protection fault" is an x86 term that doesn't really say what the issue is. I suspect this would be a "use-after-free" problem.
quoted hunk ↗ jump to hunk
with the memory debugging options. Fixes: 15becc2b56c6 ("PCI: hv: Add hv_pci_remove_slots() when we unload the driver") Signed-off-by: Dexuan Cui <decui@microsoft.com> Cc: stable@vger.kernel.org --- When pci-hyperv is unloaded, this panic can happen: general protection fault: CPU: 2 PID: 1091 Comm: rmmod Not tainted 5.2.0+ RIP: 0010:pci_slot_release+0x30/0xd0 Call Trace: kobject_release+0x65/0x190 pci_destroy_slot+0x25/0x60 hv_pci_remove+0xec/0x110 [pci_hyperv] vmbus_remove+0x20/0x30 [hv_vmbus] device_release_driver_internal+0xd5/0x1b0 driver_detach+0x44/0x7c bus_remove_driver+0x75/0xc7 vmbus_driver_unregister+0x50/0xbd [hv_vmbus] __x64_sys_delete_module+0x136/0x200 do_syscall_64+0x5e/0x220 drivers/pci/controller/pci-hyperv.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c index 6b9cc6e60a..68c611d 100644 --- a/drivers/pci/controller/pci-hyperv.c +++ b/drivers/pci/controller/pci-hyperv.c@@ -2757,8 +2757,8 @@ static int hv_pci_remove(struct hv_device *hdev) /* Remove the bus from PCI's point of view. */ pci_lock_rescan_remove(); pci_stop_root_bus(hbus->pci_bus); - pci_remove_root_bus(hbus->pci_bus); hv_pci_remove_slots(hbus); + pci_remove_root_bus(hbus->pci_bus);
I'm curious about why we need hv_pci_remove_slots() at all. None of the other callers of pci_stop_root_bus() and pci_remove_root_bus() do anything similar to hv_pci_remove_slots(). Surely some of those callers also support slots, so there must be some other path that calls pci_destroy_slot() in those cases. Can we use a similar strategy here?
pci_unlock_rescan_remove(); hbus->state = hv_pcibus_removed; } -- 1.8.3.1