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
David Hildenbrand
2021-Sep-14 09:45 UTC
[PATCH v4 3/3] virtio-mem: disallow mapping virtio-mem memory via /dev/mem
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 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 > >Yes, but I'm not able to come up with an expressive name. MEMORY_EXCLUSIVE can be highly misleading ...> the virtio change itself is ok though: > > Acked-by: Michael S. Tsirkin <mst at redhat.com>Thanks! -- Thanks, David / dhildenb