On Thu, Jan 21, 2016 at 02:57:17PM -0600, Bjorn Helgaas wrote: > Hi Sebastian, > > On Fri, Jan 15, 2016 at 07:36:25PM +0100, Sebastian Andrzej Siewior wrote: > > I start a binary which should flash the FPGA and re-enumare the PCI-BUS > > and find a new device. It works most of the time. With SLUB debug it > > crashes on each iteration with something like this (compressed output): > > > > | pcieport 0000:00:00.0: AER: Multiple Corrected error received: id=0000 > > | Unable to handle kernel paging request for data at address 0x27ef9e3e > > | Faulting instruction address: 0x602f5328 > > | Oops: Kernel access of bad area, sig: 11 [#1] > > | Workqueue: events aer_isr > > | GPR24: dd6aa000 6b6b6b6b 605f8378 605f8360 d99b12c0 604fc674 606b1704 d99b12c0 > > | NIP [602f5328] pci_walk_bus+0xd4/0x104 > > > > Register 25 has the user-after magic. As it turns out, the old PCIe > > device is leaving, generates an error before it left, aer_irq() is fired, > > it schedules a work item. What happens now is that free_irq() is > > invoked, all resources are gone *before* the aes_isr() work item is > > completed. > > So to fix this, I flush the workqueue to ensure that there is no more > > work pending. > > The wait_event() on wait_release should actually synchronized against > > removal. However the condition (->prod_idx == ->cons_idx) is made true > > before the function completes (aer_isr_one_error() is invoked right > > after that) so it does not fulfill its purpose. Therefore I remove it. > > > > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> > > I propose to merge this patch unchanged, but with the following > changelog. I want to add a bit more detail about the concurrency > problem and remove a bit of the specific detail about your FPGA: > > > commit 9963c9487f733ef8fe3a06ce3398072a40f955bf > Author: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> > Date: Fri Jan 15 19:36:25 2016 +0100 > > PCI/AER: Flush workqueue on device remove to avoid use-after-free > > A Root Port's AER structure (rpc) contains a queue of events. aer_irq() > enqueues AER status information and schedules aer_isr() to dequeue and > process it. When we remove a device, aer_remove() waits for the queue to > be empty, then frees the rpc struct. > > But aer_isr() references the rpc struct after dequeueing and possibly > emptying the queue, which can cause a use-after-free error as in the > following scenario with two threads, aer_isr() on the left and a > concurrent aer_remove() on the right: > > Thread A Thread B > -------- -------- > aer_irq(): > rpc->prod_idx++ > aer_remove(): > wait_event(rpc->prod_idx == rpc->cons_idx) > # now blocked until queue becomes empty > aer_isr(): # ... > rpc->cons_idx++ # unblocked because queue is now empty > ... kfree(rpc) > mutex_unlock(&rpc->rpc_mutex) > > Wait until the last scheduled instance of aer_isr() has completed before > freeing the rpc struct by using flush_work() in aer_remove(). > > I reproduced this use-after-free by flashing a device FPGA and > re-enumerating the bus to find the new device. With SLUB debug, this > crashes with 0x6b bytes (POISON_FREE, the use-after-free magic number) in > GPR25: > > pcieport 0000:00:00.0: AER: Multiple Corrected error received: id=0000 > Unable to handle kernel paging request for data at address 0x27ef9e3e > Workqueue: events aer_isr > GPR24: dd6aa000 6b6b6b6b 605f8378 605f8360 d99b12c0 604fc674 606b1704 d99b12c0 > NIP [602f5328] pci_walk_bus+0xd4/0x104 > > [bhelgaas: changelog] > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> > Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx> Applied to for-linus for v4.5 with stable tag, thanks! -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
