Messages in this thread | ![/](/images/icornerl.gif) | | Subject | Re: [PATCH] powerpc: Perform a bounds check in arch_add_memory | From | David Hildenbrand <> | Date | Thu, 5 Sep 2019 09:52:44 +0200 |
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On 04.09.19 07:25, Alastair D'Silva wrote: > On Mon, 2019-09-02 at 09:28 +0200, David Hildenbrand wrote: >> On 02.09.19 01:54, Alastair D'Silva wrote: >>> On Tue, 2019-08-27 at 09:13 +0200, David Hildenbrand wrote: >>>> On 27.08.19 08:39, Alastair D'Silva wrote: >>>>> On Tue, 2019-08-27 at 08:28 +0200, Michal Hocko wrote: >>>>>> On Tue 27-08-19 15:20:46, Alastair D'Silva wrote: >>>>>>> From: Alastair D'Silva <alastair@d-silva.org> >>>>>>> >>>>>>> It is possible for firmware to allocate memory ranges >>>>>>> outside >>>>>>> the range of physical memory that we support >>>>>>> (MAX_PHYSMEM_BITS). >>>>>> >>>>>> Doesn't that count as a FW bug? Do you have any evidence of >>>>>> that >>>>>> in >>>>>> the >>>>>> field? Just wondering... >>>>>> >>>>> >>>>> Not outside our lab, but OpenCAPI attached LPC memory is >>>>> assigned >>>>> addresses based on the slot/NPU it is connected to. These >>>>> addresses >>>>> prior to: >>>>> 4ffe713b7587 ("powerpc/mm: Increase the max addressable memory >>>>> to >>>>> 2PB") >>>>> were inaccessible and resulted in bogus sections - see our >>>>> discussion >>>>> on 'mm: Trigger bug on if a section is not found in >>>>> __section_nr'. >>>>> Doing this check here was your suggestion :) >>>>> >>>>> It's entirely possible that a similar problem will occur in the >>>>> future, >>>>> and it's cheap to guard against, which is why I've added this. >>>>> >>>> >>>> If you keep it here, I guess this should be wrapped by a >>>> WARN_ON_ONCE(). >>>> >>>> If we move it to common code (e.g., __add_pages() or >>>> add_memory()), >>>> then >>>> probably not. I can see that s390x allows to configure >>>> MAX_PHYSMEM_BITS, >>>> so the check could actually make sense. >>>> >>> >>> I couldn't see a nice platform indepedent way to determine the >>> allowable address range, but if there is, then I'll move this to >>> the >>> generic code instead. >>> >> >> At least on the !ZONE_DEVICE path we have >> >> __add_memory() -> register_memory_resource() ... >> >> return ERR_PTR(-E2BIG); >> >> >> I was thinking about something like >> >> int add_pages() >> { >> if ((start + size - 1) >> MAX_PHYSMEM_BITS) >> return -E2BIG; >> >> return arch_add_memory(...) >> } >> >> And switching users of arch_add_memory() to add_pages(). However, x86 >> already has an add_pages() function, so that would need some more >> thought. >> >> Maybe simply renaming the existing add_pages() to arch_add_pages(). >> >> add_pages(): Create virtual mapping >> __add_pages(): Don't create virtual mapping >> >> arch_add_memory(): Arch backend for add_pages() >> arch_add_pages(): Arch backend for __add_pages() >> >> It would be even more consistent if we would have arch_add_pages() >> vs. >> __arch_add_pages(). > > Looking a bit further, I think a good course of action would be to add > the check to memory_hotplug.c:check_hotplug_memory_range(). > > This would be the least invasive, and could check both > MAX_POSSIBLE_PHYSMEM_BITS and MAX_PHYSMEM_BITS.
You won't be able to catch the memremap path that way, just saying. But at least it would be an easy change.
> > With that in mind, we can drop this patch. >
--
Thanks,
David / dhildenb
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