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

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