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@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 ?
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@xxxxxxxxxx>
Thanks!
--
Thanks,
David / dhildenb
--
Thanks,
David / dhildenb
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