Re: [PATCH v8 1/6] PCI/ERR: get device before call device driver to avoid NULL pointer dereference

["Kuppuswamy, Sathyanarayanan" <sathyanarayanan.kuppuswamy@intel.com>]

On 10/7/20 4:31 AM, Ethan Zhao wrote:
> During DPC error injection test we found there is race condition between
> pciehp and DPC driver, NULL pointer dereference caused panic as following
>
>   # setpci -s 64:02.0 0x196.w=000a
>    // 64:02.0 is rootport has DPC capability
>   # setpci -s 65:00.0 0x04.w=0544
>    // 65:00.0 is NVMe SSD populated in above port
>   # mount /dev/nvme0n1p1 nvme
>
>   (tested on stable 5.8 & ICS(Ice Lake SP platform, see
>   https://en.wikichip.org/wiki/intel/microarchitectures/ice_lake_(server))
>
>   BUG: kernel NULL pointer dereference, address: 0000000000000050
>   ...
>   CPU: 12 PID: 513 Comm: irq/124-pcie-dp Not tainted 5.8.0-0.0.7.el8.x86_64+ #1
>   RIP: 0010:report_error_detected.cold.4+0x7d/0xe6
>   Code: b6 d0 e8 e8 fe 11 00 e8 16 c5 fb ff be 06 00 00 00 48 89 df e8 d3 65 ff
>   ff b8 06 00 00 00 e9 75 fc ff ff 48 8b 43 68 45 31 c9 <48> 8b 50 50 48 83 3a 00
>   41 0f 94 c1 45 31 c0 48 85 d2 41 0f 94 c0
>   RSP: 0018:ff8e06cf8762fda8 EFLAGS: 00010246
>   RAX: 0000000000000000 RBX: ff4e3eaacf42a000 RCX: ff4e3eb31f223c01
>   RDX: ff4e3eaacf42a140 RSI: ff4e3eb31f223c00 RDI: ff4e3eaacf42a138
>   RBP: ff8e06cf8762fdd0 R08: 00000000000000bf R09: 0000000000000000
>   R10: 000000eb8ebeab53 R11: ffffffff93453258 R12: 0000000000000002
>   R13: ff4e3eaacf42a130 R14: ff8e06cf8762fe2c R15: ff4e3eab44733828
>   FS:  0000000000000000(0000) GS:ff4e3eab1fd00000(0000) knlGS:0000000000000000
>   CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>   CR2: 0000000000000050 CR3: 0000000f8f80a004 CR4: 0000000000761ee0
>   DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>   DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>   PKRU: 55555554
>   Call Trace:
>   ? report_normal_detected+0x20/0x20
>   report_frozen_detected+0x16/0x20
>   pci_walk_bus+0x75/0x90
>   ? dpc_irq+0x90/0x90
>   pcie_do_recovery+0x157/0x201
>   ? irq_finalize_oneshot.part.47+0xe0/0xe0
>   dpc_handler+0x29/0x40
>   irq_thread_fn+0x24/0x60
>   ...
>
> Debug shows when port DPC feature was enabled and triggered by errors,
> DLLSC/PDC/DPC interrupts will be sent to pciehp and DPC driver almost
> at the same time, and no delay between them is required by specification.
> so DPC driver and pciehp drivers may handle these interrupts cocurrently.
>
> While DPC driver is doing pci_walk_bus() and calling device driver's
> callback without pci_dev_get() to increase device reference count, the
> device and its driver instance are likely being freed by
> pci_stop_and_removed_bus_device()
> -> pci_dev_put().
>
> So does pci_dev_get() before using the device instance to avoid NULL
> pointer dereference.
Won't it be better if you get this in pcie_do_recovery()?
>
> Signed-off-by: Ethan Zhao <haifeng.zhao@intel.com>
> Tested-by: Wen Jin <wen.jin@intel.com>
> Tested-by: Shanshan Zhang <ShanshanX.Zhang@intel.com>
> ---
> Changes:
>   v2: revise doc according to Andy's suggestion.
>   v3: no change.
>   v4: no change.
>   v5: no change.
>   v6: moved to [1/5] from [3/5] and revised comment according to Lukas'
>       suggestion.
>   v7: no change.
>   v8: no change.
>
>   drivers/pci/pcie/err.c | 12 ++++++++++++
>   1 file changed, 12 insertions(+)
>
> diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
> index c543f419d8f9..e35c4480c86b 100644
> --- a/drivers/pci/pcie/err.c
> +++ b/drivers/pci/pcie/err.c
> @@ -52,6 +52,8 @@ static int report_error_detected(struct pci_dev *dev,
>   	pci_ers_result_t vote;
>   	const struct pci_error_handlers *err_handler;
>   
> +	if (!pci_dev_get(dev))
> +		return 0;
>   	device_lock(&dev->dev);
>   	if (!pci_dev_set_io_state(dev, state) ||
>   		!dev->driver ||
> @@ -76,6 +78,7 @@ static int report_error_detected(struct pci_dev *dev,
>   	pci_uevent_ers(dev, vote);
>   	*result = merge_result(*result, vote);
>   	device_unlock(&dev->dev);
> +	pci_dev_put(dev);
>   	return 0;
>   }
>   
> @@ -94,6 +97,8 @@ static int report_mmio_enabled(struct pci_dev *dev, void *data)
>   	pci_ers_result_t vote, *result = data;
>   	const struct pci_error_handlers *err_handler;
>   
> +	if (!pci_dev_get(dev))
> +		return 0;
>   	device_lock(&dev->dev);
>   	if (!dev->driver ||
>   		!dev->driver->err_handler ||
> @@ -105,6 +110,7 @@ static int report_mmio_enabled(struct pci_dev *dev, void *data)
>   	*result = merge_result(*result, vote);
>   out:
>   	device_unlock(&dev->dev);
> +	pci_dev_put(dev);
>   	return 0;
>   }
>   
> @@ -113,6 +119,8 @@ static int report_slot_reset(struct pci_dev *dev, void *data)
>   	pci_ers_result_t vote, *result = data;
>   	const struct pci_error_handlers *err_handler;
>   
> +	if (!pci_dev_get(dev))
> +		return 0;
>   	device_lock(&dev->dev);
>   	if (!dev->driver ||
>   		!dev->driver->err_handler ||
> @@ -124,6 +132,7 @@ static int report_slot_reset(struct pci_dev *dev, void *data)
>   	*result = merge_result(*result, vote);
>   out:
>   	device_unlock(&dev->dev);
> +	pci_dev_put(dev);
>   	return 0;
>   }
>   
> @@ -131,6 +140,8 @@ static int report_resume(struct pci_dev *dev, void *data)
>   {
>   	const struct pci_error_handlers *err_handler;
>   
> +	if (!pci_dev_get(dev))
> +		return 0;
>   	device_lock(&dev->dev);
>   	if (!pci_dev_set_io_state(dev, pci_channel_io_normal) ||
>   		!dev->driver ||
> @@ -143,6 +154,7 @@ static int report_resume(struct pci_dev *dev, void *data)
>   out:
>   	pci_uevent_ers(dev, PCI_ERS_RESULT_RECOVERED);
>   	device_unlock(&dev->dev);
> +	pci_dev_put(dev);
>   	return 0;
>   }
>   

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer