Messages in this thread | | | Subject | Re: [PATCH v3 3/4] lib: logic_pio: Reject accesses to unregistered CPU MMIO regions | From | John Garry <> | Date | Fri, 5 Apr 2019 09:10:27 +0100 |
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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 > > . >
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