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virtio-mem-for-5.16

virtio-mem: support VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE

Support the VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE feature in virtio-mem, now
that "accidential" access to logically unplugged memory inside added
Linux memory blocks is no longer possible, because we:

1. Removed /dev/kmem in commit bbcd53c ("drivers/char: remove
   /dev/kmem for good")
2. Disallowed access to virtio-mem device memory via /dev/mem in commit
   2128f4e ("virtio-mem: disallow mapping virtio-mem memory via
   /dev/mem")
3. Sanitized access to virtio-mem device memory via /proc/kcore in
   commit 0daa322 ("fs/proc/kcore: don't read offline sections,
   logically offline pages and hwpoisoned pages")
4. Sanitized access to virtio-mem device memory via /proc/vmcore in
   commit ce28146 ("virtio-mem: kdump mode to sanitize /proc/vmcore
   access")

The new VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE feature that will be required
by some hypervisors implementing virtio-mem in the near future, so let's
support it now that we safely can.

Signed-off-by: David Hildenbrand <[email protected]>

Nov 10, 2021
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denywrite-for-5.15

Remove in-tree usage of MAP_DENYWRITE

Remove all in-tree usage of MAP_DENYWRITE from the kernel and remove
VM_DENYWRITE.

There are some (minor) user-visible changes:
1. We no longer deny write access to shared libaries loaded via legacy
   uselib(); this behavior matches modern user space e.g., via dlopen().
2. We no longer deny write access to the elf interpreter after exec
   completed, treating it just like shared libraries (which it often is).
3. We always deny write access to the file linked via /proc/pid/exe:
   sys_prctl(PR_SET_MM_MAP/EXE_FILE) will fail if write access to the file
   cannot be denied, and write access to the file will remain denied
   until the link is effectivel gone (exec, termination,
   sys_prctl(PR_SET_MM_MAP/EXE_FILE)) -- just as if exec'ing the file.

Cross-compiled for a bunch of architectures (alpha, microblaze, i386,
s390x, ...) and verified via ltp that especially the relevant tests
(i.e., creat07 and execve04) continue working as expected.

Signed-off-by: David Hildenbrand <[email protected]>