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@xxxxxxxxx> > > > Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> > > > > > > > --- > > > 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 ? > > > the virtio change itself is ok though: > > > > Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx> > > Thanks! > > > -- > Thanks, > > David / dhildenb
