David Hildenbrand
2021-Sep-02 16:09 UTC
[PATCH v4 3/3] virtio-mem: disallow mapping virtio-mem memory via /dev/mem
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 at intel.com>
Signed-off-by: David Hildenbrand <david at 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.
diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
index b91bc810a87e..c2d93492cf0f 100644
--- a/drivers/virtio/virtio_mem.c
+++ b/drivers/virtio/virtio_mem.c
@@ -2523,8 +2523,10 @@ static int virtio_mem_create_resource(struct virtio_mem
*vm)
if (!name)
return -ENOMEM;
+ /* Disallow mapping device memory via /dev/mem completely. */
vm->parent_resource = __request_mem_region(vm->addr, vm->region_size,
- name, IORESOURCE_SYSTEM_RAM);
+ name, IORESOURCE_SYSTEM_RAM |
+ IORESOURCE_EXCLUSIVE);
if (!vm->parent_resource) {
kfree(name);
dev_warn(&vm->vdev->dev, "could not reserve device
region\n");
--
2.31.1
Michael S. Tsirkin
2021-Sep-03 07:02 UTC
[PATCH v4 3/3] virtio-mem: disallow mapping virtio-mem memory via /dev/mem
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 at intel.com> > Signed-off-by: David Hildenbrand <david at 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 the virtio change itself is ok though: Acked-by: Michael S. Tsirkin <mst at redhat.com> for merging through -mm.> diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c > index b91bc810a87e..c2d93492cf0f 100644 > --- a/drivers/virtio/virtio_mem.c > +++ b/drivers/virtio/virtio_mem.c > @@ -2523,8 +2523,10 @@ static int virtio_mem_create_resource(struct virtio_mem *vm) > if (!name) > return -ENOMEM; > > + /* Disallow mapping device memory via /dev/mem completely. */ > vm->parent_resource = __request_mem_region(vm->addr, vm->region_size, > - name, IORESOURCE_SYSTEM_RAM); > + name, IORESOURCE_SYSTEM_RAM | > + IORESOURCE_EXCLUSIVE); > if (!vm->parent_resource) { > kfree(name); > dev_warn(&vm->vdev->dev, "could not reserve device region\n"); > -- > 2.31.1