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Date: Mon, 8 Apr 2019 09:01:14 +0100 From: John Garry <john.garry@...wei.com> To: Bjorn Helgaas <helgaas@...nel.org> CC: Guenter Roeck <linux@...ck-us.net>, <wangkefeng.wang@...wei.com>, <lorenzo.pieralisi@....com>, <arnd@...db.de>, <rafael@...nel.org>, <linux-pci@...r.kernel.org>, <will.deacon@....com>, <linux-kernel@...r.kernel.org>, <linuxarm@...wei.com>, <andy.shevchenko@...il.com>, <catalin.marinas@....com>, <bp@...e.de>, <linux-arm-kernel@...ts.infradead.org> Subject: Re: [PATCH v3 3/4] lib: logic_pio: Reject accesses to unregistered CPU MMIO regions On 05/04/2019 19:06, Bjorn Helgaas wrote: > On Fri, Apr 05, 2019 at 09:10:27AM +0100, John Garry wrote: >> 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"). > Correction: "As such, *on arm* even well-behaved drivers like f71882fg can still crash the system, ... So, yes, x86 - which has native IO ports - would not have this issue. > Maybe I'm missing something, but on x86, drivers like f71882fg do not > crash the system because inb() *never* causes a crash. > > If you want to build that driver for ARM, I think you need to make > sure that inb() on ARM also *never* causes a crash. I don't think > changing f71882fg and all the similar drivers is the right answer. > Right, so this is the intention of this patch. However it would be still good to find a way to fail a request to claim an IO port region if none is accessible or mapped. Thanks, John > Bjorn > > . >
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