Re: [PATCH v2] ARM: Add sanity check for dev->periphid in amba_probe()

["Leizhen (ThunderTown)" <thunder.leizhen@huawei.com>]

On 2022/8/30 17:47, Russell King (Oracle) wrote:
> On Tue, Aug 30, 2022 at 12:20:00AM -0700, Saravana Kannan wrote:
>> On Mon, Aug 29, 2022 at 11:59 PM Zhen Lei <thunder.leizhen@huawei.com> wrote:
>>>
>>> Commit f2d3b9a46e0e ("ARM: 9220/1: amba: Remove deferred device addition")
>>> forcibly invokes device_add() even if dev->periphid is not ready. Although
>>> it will be remedied in amba_match(): dev->periphid will be initialized
>>> if everything is in place; Otherwise, return -EPROBE_DEFER to block
>>> __driver_attach() from further execution. But not all drivers have .match
>>> hook, such as pl031, the dev->bus->probe will be called directly in
>>> __driver_attach(). Unfortunately, if dev->periphid is still not
>>> initialized, the following exception will be triggered.
>>>
>>> 8<--- cut here ---
>>> Unable to handle kernel NULL pointer dereference at virtual address 00000008
>>> [00000008] *pgd=00000000
>>> Internal error: Oops: 5 [#1] SMP ARM
>>> Modules linked in:
>>> CPU: 1 PID: 1 Comm: swapper/0 Not tainted 6.0.0-rc2+ #7
>>> Hardware name: ARM-Versatile Express
>>> PC is at pl031_probe+0x8/0x208
>>> LR is at amba_probe+0xf0/0x160
>>> pc : 80698df8  lr : 8050eb54  psr: 80000013
>>> sp : c0825df8  ip : 00000000  fp : 811fda38
>>> r10: 00000000  r9 : 80d72470  r8 : fffffdfb
>>> r7 : 811fd800  r6 : be7eb330  r5 : 00000000  r4 : 811fd900
>>> r3 : 80698df0  r2 : 37000000  r1 : 00000000  r0 : 811fd800
>>> Flags: Nzcv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
>>> Control: 10c5387d  Table: 6000406a  DAC: 00000051
>>> ... ...
>>>  pl031_probe from amba_probe+0xf0/0x160
>>>  amba_probe from really_probe+0x118/0x290
>>>  really_probe from __driver_probe_device+0x84/0xe4
>>>  __driver_probe_device from driver_probe_device+0x30/0xd0
>>>  driver_probe_device from __driver_attach+0x8c/0xfc
>>>  __driver_attach from bus_for_each_dev+0x70/0xb0
>>>  bus_for_each_dev from bus_add_driver+0x168/0x1f4
>>>  bus_add_driver from driver_register+0x7c/0x118
>>>  driver_register from do_one_initcall+0x44/0x1ec
>>>  do_one_initcall from kernel_init_freeable+0x238/0x288
>>>  kernel_init_freeable from kernel_init+0x18/0x12c
>>>  kernel_init from ret_from_fork+0x14/0x2c
>>> ... ...
>>> ---[ end trace 0000000000000000 ]---
>>>
>>> Therefore, take the same action as in amba_match(): return -EPROBE_DEFER
>>> if dev->periphid is not ready in amba_probe().
>>>
>>> Fixes: f2d3b9a46e0e ("ARM: 9220/1: amba: Remove deferred device addition")
>>> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
>>> ---
>>> KernelVersion: v6.0-rc3
>>>  drivers/amba/bus.c | 24 +++++++++++++++++++++---
>>>  1 file changed, 21 insertions(+), 3 deletions(-)
>>>
>>> v1 --> v2:
>>> 1. Update this patch based on:
>>>    https://lore.kernel.org/lkml/20220818172852.3548-1-isaacmanjarres@google.com/
>>> 2. Move the operations of sanity checking and reading dev->periphid,
>>>    updating uevent into new function amba_prepare_periphid().
>>>
>>> diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c
>>> index 110a535648d2e1f..8e4c7e190880206 100644
>>> --- a/drivers/amba/bus.c
>>> +++ b/drivers/amba/bus.c
>>> @@ -204,10 +204,9 @@ static int amba_read_periphid(struct amba_device *dev)
>>>         return ret;
>>>  }
>>>
>>> -static int amba_match(struct device *dev, struct device_driver *drv)
>>> +static int amba_prepare_periphid(struct device *dev)
>>>  {
>>>         struct amba_device *pcdev = to_amba_device(dev);
>>> -       struct amba_driver *pcdrv = to_amba_driver(drv);
>>>
>>>         mutex_lock(&pcdev->periphid_lock);
>>>         if (!pcdev->periphid) {
>>> @@ -228,6 +227,19 @@ static int amba_match(struct device *dev, struct device_driver *drv)
>>>         }
>>>         mutex_unlock(&pcdev->periphid_lock);
>>>
>>> +       return 0;
>>> +}
>>> +
>>> +static int amba_match(struct device *dev, struct device_driver *drv)
>>> +{
>>> +       struct amba_device *pcdev = to_amba_device(dev);
>>> +       struct amba_driver *pcdrv = to_amba_driver(drv);
>>> +       int ret;
>>> +
>>> +       ret = amba_prepare_periphid(dev);
>>> +       if (ret)
>>> +               return ret;
>>> +
>>>         /* When driver_override is set, only bind to the matching driver */
>>>         if (pcdev->driver_override)
>>>                 return !strcmp(pcdev->driver_override, drv->name);
>>> @@ -278,9 +290,15 @@ static int amba_probe(struct device *dev)
>>>  {
>>>         struct amba_device *pcdev = to_amba_device(dev);
>>>         struct amba_driver *pcdrv = to_amba_driver(dev->driver);
>>> -       const struct amba_id *id = amba_lookup(pcdrv->id_table, pcdev);
>>> +       const struct amba_id *id;
>>>         int ret;
>>>
>>> +       ret = amba_prepare_periphid(dev);
>>> +       if (ret)
>>> +               return ret;
>>> +
>>> +       id = amba_lookup(pcdrv->id_table, pcdev);
>>> +
>>>         do {
>>>                 ret = of_amba_device_decode_irq(pcdev);
>>>                 if (ret)
>>
>> Let's wait for Isaac to review this. He has been looking at the
>> locking issue for a bit and there were some tricky cases.
> 
> How can we get to amba_probe() if amba_match() has not returned a
> positive match for an ID? Surely if that happens, the driver model

Always return true.

__driver_attach
    driver_match_device

static inline int driver_match_device(struct device_driver *drv,
                                      struct device *dev)
{
        return drv->bus->match ? drv->bus->match(dev, drv) : 1;
}

> is failed - since a probe function should not be called unless the
> driver matches the device.
> 
> This patch, and 9229/1 both feel like they're working around some
> brokenness elsewhere in the kernel.
> 
> The description in 9229/1, specifically "But not all drivers have .match
> hook, such as pl031, the dev->bus->probe will be called directly in
> __driver_attach()." AMBA drivers do not have a .match hook - the bus
> does, which all AMBA drivers must be a member of. If amba_match fails,
> there is no way that amba_probe() should ever be called.
> 

-- 
Regards,
  Zhen Lei