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Tsirkin" To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, Arnd Bergmann , Greg Kroah-Hartman , Jason Wang , "Rafael J. Wysocki" , Andrew Morton , Dan Williams , Hanjun Guo , Andy Shevchenko , virtualization@lists.linux-foundation.org, linux-mm@kvack.org Subject: Re: [PATCH v4 3/3] virtio-mem: disallow mapping virtio-mem memory via /dev/mem Message-ID: <20210914080213-mutt-send-email-mst@kernel.org> References: <20210902160919.25683-1-david@redhat.com> <20210902160919.25683-4-david@redhat.com> <20210903025630-mutt-send-email-mst@kernel.org> <20210914075046-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Authentication-Results: imf10.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=aGBFXbsc; spf=none (imf10.hostedemail.com: domain of mst@redhat.com has no SPF policy when checking 216.205.24.124) smtp.mailfrom=mst@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: DBEA86001996 X-Stat-Signature: xq7ukzc5w5odb876zx8rbkcdq4sncpyn X-HE-Tag: 1631621056-724257 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Sep 14, 2021 at 01:57:25PM +0200, David Hildenbrand wrote: > 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 > > > > > Signed-off-by: David Hildenbrand > > > > > > > > > > > > > --- > > > > > 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 ? OK. > > > > > > > > > the virtio change itself is ok though: > > > > > > > > Acked-by: Michael S. Tsirkin > > > > > > Thanks! > > > > > > > > > -- > > > Thanks, > > > > > > David / dhildenb > > > > > -- > Thanks, > > David / dhildenb