Messages in this thread | | | Subject | Re: [PATCH v4 3/3] virtio-mem: disallow mapping virtio-mem memory via /dev/mem | From | David Hildenbrand <> | Date | Tue, 14 Sep 2021 13:57:25 +0200 |
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On 14.09.21 13:52, Michael S. Tsirkin wrote: > On Tue, Sep 14, 2021 at 11:45:25AM +0200, David Hildenbrand wrote: >> On 03.09.21 09:02, Michael S. Tsirkin wrote: >>> On Thu, Sep 02, 2021 at 06:09:19PM +0200, David Hildenbrand wrote: >>>> We don't want user space to be able to map virtio-mem device memory >>>> directly (e.g., via /dev/mem) in order to have guarantees that in a sane >>>> setup we'll never accidentially access unplugged memory within the >>>> device-managed region of a virtio-mem device, just as required by the >>>> virtio-spec. >>>> >>>> As soon as the virtio-mem driver is loaded, the device region is visible >>>> in /proc/iomem via the parent device region. From that point on user space >>>> is aware of the device region and we want to disallow mapping anything >>>> inside that region (where we will dynamically (un)plug memory) until >>>> the driver has been unloaded cleanly and e.g., another driver might take >>>> over. >>>> >>>> By creating our parent IORESOURCE_SYSTEM_RAM resource with >>>> IORESOURCE_EXCLUSIVE, we will disallow any /dev/mem access to our >>>> device region until the driver was unloaded cleanly and removed the >>>> parent region. This will work even though only some memory blocks are >>>> actually currently added to Linux and appear as busy in the resource tree. >>>> >>>> So access to the region from user space is only possible >>>> a) if we don't load the virtio-mem driver. >>>> b) after unloading the virtio-mem driver cleanly. >>>> >>>> Don't build virtio-mem if access to /dev/mem cannot be restricticted -- >>>> if we have CONFIG_DEVMEM=y but CONFIG_STRICT_DEVMEM is not set. >>>> >>>> Reviewed-by: Dan Williams <dan.j.williams@intel.com> >>>> Signed-off-by: David Hildenbrand <david@redhat.com> >>> >>> >>>> --- >>>> drivers/virtio/Kconfig | 1 + >>>> drivers/virtio/virtio_mem.c | 4 +++- >>>> 2 files changed, 4 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig >>>> index ce1b3f6ec325..ff80cd03f1d1 100644 >>>> --- a/drivers/virtio/Kconfig >>>> +++ b/drivers/virtio/Kconfig >>>> @@ -101,6 +101,7 @@ config VIRTIO_MEM >>>> depends on MEMORY_HOTPLUG_SPARSE >>>> depends on MEMORY_HOTREMOVE >>>> depends on CONTIG_ALLOC >>>> + depends on !DEVMEM || STRICT_DEVMEM >>>> help >>>> This driver provides access to virtio-mem paravirtualized memory >>>> devices, allowing to hotplug and hotunplug memory. >>> >>> It would be nicer if there was a symbol in the MEMORY_ namespace >>> we can depend on exported by mm and depending on !DEVMEM || >>> STRICT_DEVMEM. >>> >>> E.g. >>> >>> config MEMORY_EXCLUSIVE >>> def_bool y >>> depends on !DEVMEM || STRICT_DEVMEM >>> >>> and then in virtio >>> depends on MEMORY_EXCLUSIVE >>> >>> >> >> Yes, but I'm not able to come up with an expressive name. MEMORY_EXCLUSIVE >> can be highly misleading ... > > > I mean ... it enables IORESOURCE_EXCLUSIVE ... but ok ... > MEMORY_EXCLUSIVE_KERNEL_MAP ?
It enables IORESOURCE_EXCLUSIVE for IORESOURCE_SYSTEM_RAM ... and notably not for IORESOURCE_MEM.
MEMORY_EXCLUSIVE_SYSTEM_RAM ?
> >> >>> the virtio change itself is ok though: >>> >>> Acked-by: Michael S. Tsirkin <mst@redhat.com> >> >> Thanks! >> >> >> -- >> Thanks, >> >> David / dhildenb >
-- Thanks,
David / dhildenb
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