Looking for places where the kernel might unconditionally read
PageOffline() pages, I stumbled over /proc/kcore; turns out /proc/kcore
needs some more love to not touch some other pages we really don't want to
read -- i.e., hwpoisoned ones.
Examples for PageOffline() pages are pages inflated in a balloon,
memory unplugged via virtio-mem, and partially-present sections in
memory added by the Hyper-V balloon.
When reading pages inflated in a balloon, we essentially produce
unnecessary load in the hypervisor; holes in partially present sections in
case of Hyper-V are not accessible and already were a problem for
/proc/vmcore, fixed in makedumpfile by detecting PageOffline() pages. In
the future, virtio-mem might disallow reading unplugged memory -- marked
as PageOffline() -- in some environments, resulting in undefined behavior
when accessed; therefore, I'm trying to identify and rework all these
(corner) cases.
With this series, there is really only access via /dev/mem, /proc/vmcore
and kdb left after I ripped out /dev/kmem. kdb is an advanced corner-case
use case -- we won't care for now if someone explicitly tries to do nasty
things by reading from/writing to physical addresses we better not touch.
/dev/mem is a use case we won't support for virtio-mem, at least for now,
so we'll simply disallow mapping any virtio-mem memory via /dev/mem next.
/proc/vmcore is really only a problem when dumping the old kernel via
something that's not makedumpfile (read: basically never), however, we'll
try sanitizing that as well in the second kernel in the future.
Tested via kcore_dump:
https://github.com/schlafwandler/kcore_dump
v1 -> v2:
- Dropped "mm: rename and move page_is_poisoned()"
- "fs/proc/kcore: don't read offline sections, logically offline pages ..."
-- Add is_page_hwpoison() in page-flags.h along with a comment
- "mm: introduce page_offline_(begin|end|freeze|thaw) to ..."
-- s/unfreeze/thaw/
-- Add a comment to PageOffline documentation in page-flags.h
- "virtio-mem: use page_offline_(start|end) when setting PageOffline()"
-- Extend patch description
- "fs/proc/kcore: use page_offline_(freeze|thaw)"
-- Simplify freeze/thaw logic
- Collected acks/rbs
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <redacted>
Cc: Alexey Dobriyan <redacted>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Roman Gushchin <redacted>
Cc: Alex Shi <redacted>
Cc: Steven Price <steven.price@arm.com>
Cc: Mike Kravetz <redacted>
Cc: Aili Yao <redacted>
Cc: Jiri Bohac <redacted>
Cc: "K. Y. Srinivasan" <redacted>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Stephen Hemminger <redacted>
Cc: Wei Liu <wei.liu@kernel.org>
Cc: Naoya Horiguchi <redacted>
Cc: <redacted>
Cc: <redacted>
Cc: <redacted>
Cc: <redacted>
David Hildenbrand (6):
fs/proc/kcore: drop KCORE_REMAP and KCORE_OTHER
fs/proc/kcore: pfn_is_ram check only applies to KCORE_RAM
fs/proc/kcore: don't read offline sections, logically offline pages
and hwpoisoned pages
mm: introduce page_offline_(begin|end|freeze|thaw) to synchronize
setting PageOffline()
virtio-mem: use page_offline_(start|end) when setting PageOffline()
fs/proc/kcore: use page_offline_(freeze|thaw)
drivers/virtio/virtio_mem.c | 2 ++
fs/proc/kcore.c | 67 ++++++++++++++++++++++++++++++-------
include/linux/kcore.h | 3 --
include/linux/page-flags.h | 22 ++++++++++++
mm/util.c | 40 ++++++++++++++++++++++
5 files changed, 118 insertions(+), 16 deletions(-)
base-commit: 6efb943b8616ec53a5e444193dccf1af9ad627b5
--
2.31.1
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