[PATCH v1 0/8] proc/vmcore: sanitize access to virtio-mem memory

[David Hildenbrand]

As so often with virtio-mem changes that mess with common MM
infrastructure, this might be a good candiate to go via Andrew's tree.

--

After removing /dev/kmem, sanitizing /proc/kcore and handling /dev/mem,
this series tackles the last sane way how a VM could accidentially access
logically unplugged memory managed by a virtio-mem device: /proc/vmcore

When dumping memory via "makedumpfile", PG_offline pages, used by
virtio-mem to flag logically unplugged memory, are already properly
excluded; however, especially when accessing/copying /proc/vmcore "the
usual way", we can still end up reading logically unplugged memory part of
a virtio-mem device.

Patch #1-#3 are cleanups. Patch #4 extends the existing oldmem_pfn_is_ram
mechanism. Patch #5-#7 are virtio-mem refactorings for patch #8, which
implements the virtio-mem logic to query the state of device blocks.

Patch #8:

"
Although virtio-mem currently supports reading unplugged memory in the
hypervisor, this will change in the future, indicated to the device via
a new feature flag. We similarly sanitized /proc/kcore access recently.
[...]
Distributions that support virtio-mem+kdump have to make sure that the
virtio_mem module will be part of the kdump kernel or the kdump initrd;
dracut was recently [2] extended to include virtio-mem in the generated
initrd. As long as no special kdump kernels are used, this will
automatically make sure that virtio-mem will be around in the kdump initrd
and sanitize /proc/vmcore access -- with dracut.
"

This is the last remaining bit to support
VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE [3] in the Linux implementation of
virtio-mem.

Note: this is best-effort. We'll never be able to control what runs inside
the second kernel, really, but we also don't have to care: we only care
about sane setups where we don't want our VM getting zapped once we
touch the wrong memory location while dumping. While we usually expect sane
setups to use "makedumfile", nothing really speaks against just copying
/proc/vmcore, especially in environments where HWpoisioning isn't typically
expected. Also, we really don't want to put all our trust completely on the
memmap, so sanitizing also makes sense when just using "makedumpfile".

[1] https://lkml.kernel.org/r/20210526093041.8800-1-david@xxxxxxxxxx
[2] https://github.com/dracutdevs/dracut/pull/1157
[3] https://lists.oasis-open.org/archives/virtio-comment/202109/msg00021.html

Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
Cc: Jason Wang <jasowang@xxxxxxxxxx>
Cc: Dave Young <dyoung@xxxxxxxxxx>
Cc: Baoquan He <bhe@xxxxxxxxxx>
Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxx>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@xxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
Cc: kexec@xxxxxxxxxxxxxxxxxxx
Cc: linux-fsdevel@xxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx

David Hildenbrand (8):
  x86/xen: update xen_oldmem_pfn_is_ram() documentation
  x86/xen: simplify xen_oldmem_pfn_is_ram()
  proc/vmcore: let pfn_is_ram() return a bool
  proc/vmcore: convert oldmem_pfn_is_ram callback to more generic vmcore
    callbacks
  virtio-mem: factor out hotplug specifics from virtio_mem_init() into
    virtio_mem_init_hotplug()
  virtio-mem: factor out hotplug specifics from virtio_mem_probe() into
    virtio_mem_init_hotplug()
  virtio-mem: factor out hotplug specifics from virtio_mem_remove() into
    virtio_mem_deinit_hotplug()
  virtio-mem: kdump mode to sanitize /proc/vmcore access

 arch/x86/kernel/aperture_64.c |  13 +-
 arch/x86/xen/mmu_hvm.c        |  31 ++--
 drivers/virtio/virtio_mem.c   | 297 ++++++++++++++++++++++++----------
 fs/proc/vmcore.c              | 105 ++++++++----
 include/linux/crash_dump.h    |  26 ++-
 5 files changed, 332 insertions(+), 140 deletions(-)


base-commit: 5816b3e6577eaa676ceb00a848f0fd65fe2adc29
-- 
2.31.1