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Message-ID: <ca7adc9d-9df3-4050-8943-3c489097b995@163.com>
Date: Thu, 30 May 2024 21:33:03 +0800
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Subject: Re: [PATCH v2] Bluetooth: qca: Fix BT enable failure again for
 QCA6390 after warm reboot
From: Lk Sii <lk_sii@163.com>
To: Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Cc: Zijun Hu <quic_zijuhu@quicinc.com>, luiz.von.dentz@intel.com,
 marcel@holtmann.org, linux-bluetooth@vger.kernel.org, wt@penguintechs.org,
 regressions@lists.linux.dev, pmenzel@molgen.mpg.de,
 krzysztof.kozlowski@linaro.org, stable@vger.kernel.org
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On 2024/5/23 08:17, Lk Sii wrote:
> 
> 
> On 2024/5/21 23:48, Luiz Augusto von Dentz wrote:
>> Hi,
>>
>> On Tue, May 21, 2024 at 10:52 AM Lk Sii <lk_sii@163.com> wrote:
>>>
>>>
>>>
>>> On 2024/5/16 23:55, Luiz Augusto von Dentz wrote:
>>>> Hi,
>>>>
>>>> On Thu, May 16, 2024 at 10:57 AM Lk Sii <lk_sii@163.com> wrote:
>>>>>
>>>>>
>>>>>
>>>>> On 2024/5/16 21:31, Zijun Hu wrote:
>>>>>> Commit 272970be3dab ("Bluetooth: hci_qca: Fix driver shutdown on closed
>>>>>> serdev") will cause below regression issue:
>>>>>>
>>>>>> BT can't be enabled after below steps:
>>>>>> cold boot -> enable BT -> disable BT -> warm reboot -> BT enable failure
>>>>>> if property enable-gpios is not configured within DT|ACPI for QCA6390.
>>>>>>
>>>>>> The commit is to fix a use-after-free issue within qca_serdev_shutdown()
>>>>>> by adding condition to avoid the serdev is flushed or wrote after closed
>>>>>> but also introduces this regression issue regarding above steps since the
>>>>>> VSC is not sent to reset controller during warm reboot.
>>>>>>
>>>>>> Fixed by sending the VSC to reset controller within qca_serdev_shutdown()
>>>>>> once BT was ever enabled, and the use-after-free issue is also fixed by
>>>>>> this change since the serdev is still opened before it is flushed or wrote.
>>>>>>
>>>>>> Verified by the reported machine Dell XPS 13 9310 laptop over below two
>>>>>> kernel commits:
>>>>>> commit e00fc2700a3f ("Bluetooth: btusb: Fix triggering coredump
>>>>>> implementation for QCA") of bluetooth-next tree.
>>>>>> commit b23d98d46d28 ("Bluetooth: btusb: Fix triggering coredump
>>>>>> implementation for QCA") of linus mainline tree.
>>>>>>
>>>>>> Fixes: 272970be3dab ("Bluetooth: hci_qca: Fix driver shutdown on closed serdev")
>>>>>> Cc: stable@vger.kernel.org
>>>>>> Reported-by: Wren Turkal <wt@penguintechs.org>
>>>>>> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218726
>>>>>> Signed-off-by: Zijun Hu <quic_zijuhu@quicinc.com>
>>>>>> Tested-by: Wren Turkal <wt@penguintechs.org>
>>>>>> ---
>>>>>> V1 -> V2: Add comments and more commit messages
>>>>>>
>>>>>> V1 discussion link:
>>>>>> https://lore.kernel.org/linux-bluetooth/d553edef-c1a4-4d52-a892-715549d31ebe@163.com/T/#t
>>>>>>
>>>>>>  drivers/bluetooth/hci_qca.c | 18 +++++++++++++++---
>>>>>>  1 file changed, 15 insertions(+), 3 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/bluetooth/hci_qca.c b/drivers/bluetooth/hci_qca.c
>>>>>> index 0c9c9ee56592..9a0bc86f9aac 100644
>>>>>> --- a/drivers/bluetooth/hci_qca.c
>>>>>> +++ b/drivers/bluetooth/hci_qca.c
>>>>>> @@ -2450,15 +2450,27 @@ static void qca_serdev_shutdown(struct device *dev)
>>>>>>       struct qca_serdev *qcadev = serdev_device_get_drvdata(serdev);
>>>>>>       struct hci_uart *hu = &qcadev->serdev_hu;
>>>>>>       struct hci_dev *hdev = hu->hdev;
>>>>>> -     struct qca_data *qca = hu->priv;
>>>>>>       const u8 ibs_wake_cmd[] = { 0xFD };
>>>>>>       const u8 edl_reset_soc_cmd[] = { 0x01, 0x00, 0xFC, 0x01, 0x05 };
>>>>>>
>>>>>>       if (qcadev->btsoc_type == QCA_QCA6390) {
>>>>>> -             if (test_bit(QCA_BT_OFF, &qca->flags) ||
>>>>>> -                 !test_bit(HCI_RUNNING, &hdev->flags))
>>>>>> +             /* The purpose of sending the VSC is to reset SOC into a initial
>>>>>> +              * state and the state will ensure next hdev->setup() success.
>>>>>> +              * if HCI_QUIRK_NON_PERSISTENT_SETUP is set, it means that
>>>>>> +              * hdev->setup() can do its job regardless of SoC state, so
>>>>>> +              * don't need to send the VSC.
>>>>>> +              * if HCI_SETUP is set, it means that hdev->setup() was never
>>>>>> +              * invoked and the SOC is already in the initial state, so
>>>>>> +              * don't also need to send the VSC.
>>>>>> +              */
>>>>>> +             if (test_bit(HCI_QUIRK_NON_PERSISTENT_SETUP, &hdev->quirks) ||
>>>>>> +                 hci_dev_test_flag(hdev, HCI_SETUP))
>>>>>>                       return;
>>> The main purpose of above checking is NOT to make sure the serdev within
>>> open state as its comments explained.
>>>>>>
>>>>>> +             /* The serdev must be in open state when conrol logic arrives
>>>>>> +              * here, so also fix the use-after-free issue caused by that
>>>>>> +              * the serdev is flushed or wrote after it is closed.
>>>>>> +              */
>>>>>>               serdev_device_write_flush(serdev);
>>>>>>               ret = serdev_device_write_buf(serdev, ibs_wake_cmd,
>>>>>>                                             sizeof(ibs_wake_cmd));
>>>>> i believe Zijun's change is able to fix both below issues and don't
>>>>> introduce new issue.
>>>>>
>>>>> regression issue A:  BT enable failure after warm reboot.
>>>>> issue B:  use-after-free issue, namely, kernel crash.
>>>>>
>>>>>
>>>>> For issue B, i have more findings related to below commits ordered by time.
>>>>>
>>>>> Commit A: 7e7bbddd029b ("Bluetooth: hci_qca: Fix qca6390 enable failure
>>>>> after warm reboot")
>>>>>
>>>>> Commit B: de8892df72be ("Bluetooth: hci_serdev: Close UART port if
>>>>> NON_PERSISTENT_SETUP is set")
>>>>> this commit introduces issue B, it is also not suitable to associate
>>>>> protocol state with state of lower level transport type such as serdev
>>>>> or uart, in my opinion, protocol state should be independent with
>>>>> transport type state, flag HCI_UART_PROTO_READY is for protocol state,
>>>>> it means if protocol hu->proto is initialized and if we can invoke its
>>>>> interfaces.it is common for various kinds of transport types. perhaps,
>>>>> this is the reason why Zijun's change doesn't use flag HCI_UART_PROTO_READY.
>>>>
>>>> Don't really follow you here, if HCI_UART_PROTO_READY indicates the
>>>> protocol state they is even _more_ important to use before invoking
>>>> serdev APIs, so checking for the quirk sound like a problem because:
>>>>
>>>> [1] hci_uart_close
>>>>      /* When QUIRK HCI_QUIRK_NON_PERSISTENT_SETUP is set by driver,
>>>>      * BT SOC is completely powered OFF during BT OFF, holding port
>>>>      * open may drain the battery.
>>>>      */
>>>>     if (test_bit(HCI_QUIRK_NON_PERSISTENT_SETUP, &hdev->quirks)) {
>>>>         clear_bit(HCI_UART_PROTO_READY, &hu->flags);
>>>>         serdev_device_close(hu->serdev);
>>>>     }
>>>>
>>>> [2] hci_uart_unregister_device
>>>>     if (test_bit(HCI_UART_PROTO_READY, &hu->flags)) {
>>>>         clear_bit(HCI_UART_PROTO_READY, &hu->flags);
>>>>         serdev_device_close(hu->serdev);
>>>>     }
>>>> both case 1 and case 2 were introduced by Commit B in question which
>>> uses protocol state flag HCI_UART_PROTO_READY to track lower level
>>> transport type state, i don't think it is perfect.
>>>
>>> for common files hci_serdev.c and hci_ldisc.c, as you saw, the purpose
>>> of checking HCI_UART_PROTO_READY is to call protocol relevant
>>> interfaces, moreover, these protocol relevant interfaces do not deal
>>> with lower transport state. you maybe even notice below present function
>>> within which lower level serdev is flushed before HCI_UART_PROTO_READY
>>> is checked:
>>>
>>> static int hci_uart_flush(struct hci_dev *hdev)
>>> {
>>> ......
>>>         /* Flush any pending characters in the driver and discipline. */
>>>         serdev_device_write_flush(hu->serdev);
>>>
>>>         if (test_bit(HCI_UART_PROTO_READY, &hu->flags))
>>>                 hu->proto->flush(hu);
>>>
>>>         return 0;
>>> }
>>>
>>> in my opinion, that is why qca_serdev_shutdown() does not check
>>> HCI_UART_PROTO_READY for later lower level serdev operations.
>>>> So only in case 1 checking the quirk is equivalent to
>>>> HCI_UART_PROTO_READY on case 2 it does actually check the quirk and
>>>> will proceed to call serdev_device_close, now perhaps the code is
>>>> assuming that shutdown won't be called after that, but it looks it
>>>> does since:
>>>>
>>> qca_serdev_shutdown() will never be called after case 2 as explained
>>> in the end.
>>>> static void serdev_drv_remove(struct device *dev)
>>>> {
>>>>     const struct serdev_device_driver *sdrv =
>>>> to_serdev_device_driver(dev->driver);
>>>>     if (sdrv->remove)
>>>>         sdrv->remove(to_serdev_device(dev));
>>>>
>>>>     dev_pm_domain_detach(dev, true);
>>>> }
>>>>
>>>> dev_pm_domain_detach says it will power off so I assume that means
>>>> that shutdown will be called _after_ remove, so not I'm not really
>>>> convinced that we can avoid using HCI_UART_PROTO_READY, in fact the
>>>> following sequence might always be triggering:
>>>>
>>> dev_pm_domain_detach() should be irrelevant with qca_serdev_shutdown(),
>>> should not trigger call of qca_serdev_shutdown() as explained in the end
>>>> serdev_drv_remove -> qca_serdev_remove -> hci_uart_unregister_device
>>>> -> serdev_device_close -> qca_close -> kfree(qca)
>>>> dev_pm_domain_detach -> ??? -> qca_serdev_shutdown
>>>>
>>>> If this sequence is correct then qca_serdev_shutdown accessing
>>>> qca_data will always result in a UAF problem.
>>>>
>>> above sequence should not correct as explained below.
>>>
>>> serdev and its driver should also follow below generic device and driver
>>> design.
>>>
>>> 1)
>>> driver->shutdown() will be called during shut-down time at this time
>>> driver->remove() should not have been called.
>>>
>>> 2)
>>> driver->shutdown() is impossible to be called once driver->remove()
>>> was called.
>>>
>>> 3) for serdev, driver->remove() does not trigger call of
>>> driver->shutdown() since PM relevant poweroff is irrelevant with
>>> driver->shutdown() and i also don't find any PM relevant interfaces will
>>> call driver->shutdown().
>>>
>>> i would like to explain issue B based on comments Zijun posted by public
>>> as below:
>>>
>>> issue B actually happens during reboot and let me look at these steps
>>> boot -> enable BT -> disable BT -> reboot.
>>>
>>> 1) step boot will call driver->probe() to register hdev and the serdev
>>> is opened after boot.
>>>
>>> 2) step enable will call hdev->open() and the serdev will still in open
>>> state
>>>
>>> 3) step disable will call hdev->close() and the serdev will be closed
>>> after hdev->close() for machine with config which results in
>>> HCI_QUIRK_NON_PERSISTENT_SETUP is set.
>>>
>>> 4) step reboot will call qca_serdev_shutdown() which will flush and
>>> write the serdev which are closed by above step disable, so cause the
>>> UAF issue, namely, kernel crash issue.
>>>
>>> so this issue is caused by commit B which close the serdev during
>>> hdev->close().
>>>
>>> driver->remove() even is not triggered during above steps.
>>>>> Commit C: 272970be3dab ("Bluetooth: hci_qca: Fix driver shutdown on
>>>>> closed serdev")
>>>>> this commit is to fix issue B which is actually caused by Commit B, but
>>>>> it has Fixes tag for Commit A. and it also introduces the regression
>>>>> issue A.
>>>>>
>>>>
>>>>
>>
>> Reading again the commit message for the UAF fix it sounds like a
>> different problem:
>>
>>     The driver shutdown callback (which sends EDL_SOC_RESET to the device
>>     over serdev) should not be invoked when HCI device is not open (e.g. if
>>     hci_dev_open_sync() failed), because the serdev and its TTY are not open
>>     either.  Also skip this step if device is powered off
>>     (qca_power_shutdown()).
>>
>> So if hci_dev_open_sync has failed it says serdev and its TTY will not
>> be open either, so I guess that's why HCI_SETUP was added as a
>> condition to bail out? So it seems correct to do that although I'd
>> change the comments.
>>
> yes, agree with you on these points, Zijun's change is able to fix this
> different problem as well.
@Luiz:
do you have any other concerns?
how to move forward ?
>> @Krzysztof Kozlowski do you still have a test setup for 272970be3dab
>> ("Bluetooth: hci_qca: Fix driver shutdown on closed serdev"), can you
>> try with these changes?
>>