Re: [PATCH v3 3/4] lib: logic_pio: Reject accesses to unregistered CPU MMIO regions

[John Garry <john.garry@huawei.com>]

On 04/04/2019 19:58, Bjorn Helgaas wrote:
> On Thu, Apr 04, 2019 at 10:43:36AM -0700, Guenter Roeck wrote:
>> On Thu, Apr 04, 2019 at 05:52:35PM +0100, John Garry wrote:
>>>>> Note that the f71805f driver does not call
>>>>> request_{muxed_}region(), as it should.
>>>
>>>> ... which is the real problem, one that is not solved by this
>>>> patch. This may result in parallel and descructive accesses if
>>>> there is another device on the LPC bus, and another driver
>>>> accessing that device. Personally I'd rather have
>>>> request_muxed_region() added to the f71805f driver.
>>>
>>> Right, we should and will still fix f71805f. If you recall, I did
>>> have the f71805f fix in the v1 series, but you committed that it
>>> was orthogonal, so I decided to take it out of this work for now.
>>>
>>> And even if we fix up f71805f and other known drivers which don't
>>> call request_muxed_region(), we still need to police against these
>>> rogue accesses, which is what this patch attempts to do.
>>>
>> Do we ? I am personally not convinced that LPC accesses _have_ to
>> occur through PCI on any given system.
>
> On current systems, I suspect ISA/LPC devices are typically connected
> via a PCI-to-ISA/LPC bridge.  But AFAIK there's no actual requirement
> for that bridge, and there certainly *were* systems with ISA devices
> but no PCI at all.
>
> IMO, if you want to build ISA drivers on your arch, you need to make
> sure the inb() probing done by those drivers works like it does on
> x86.  If there's no device there, the inb() should return 0xff with no
> fuss and no crash.

Right, and this is what I am attempting to do here.

So today a call to request_muxed_region() can still succeed even if no 
IO space mapped.

As such, even well-behaved drivers like f71882fg can still crash the 
system, as noted in RFC patch 1/4 ("resource: Request IO port regions 
from children of ioport_resource").

Thanks,
John

>
> Bjorn
>
> .
>