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Halil Pasic f5c147c0d9 virtio: write back F_VERSION_1 before validate 
commit 2f9a174f91 upstream.

The virtio specification virtio-v1.1-cs01 states: "Transitional devices
MUST detect Legacy drivers by detecting that VIRTIO_F_VERSION_1 has not
been acknowledged by the driver."  This is exactly what QEMU as of 6.1
has done relying solely on VIRTIO_F_VERSION_1 for detecting that.

However, the specification also says: "... the driver MAY read (but MUST
NOT write) the device-specific configuration fields to check that it can
support the device ..." before setting FEATURES_OK.

In that case, any transitional device relying solely on
VIRTIO_F_VERSION_1 for detecting legacy drivers will return data in
legacy format.  In particular, this implies that it is in big endian
format for big endian guests. This naturally confuses the driver which
expects little endian in the modern mode.

It is probably a good idea to amend the spec to clarify that
VIRTIO_F_VERSION_1 can only be relied on after the feature negotiation
is complete. Before validate callback existed, config space was only
read after FEATURES_OK. However, we already have two regressions, so
let's address this here as well.

The regressions affect the VIRTIO_NET_F_MTU feature of virtio-net and
the VIRTIO_BLK_F_BLK_SIZE feature of virtio-blk for BE guests when
virtio 1.0 is used on both sides. The latter renders virtio-blk unusable
with DASD backing, because things simply don't work with the default.
See Fixes tags for relevant commits.

For QEMU, we can work around the issue by writing out the feature bits
with VIRTIO_F_VERSION_1 bit set.  We (ab)use the finalize_features
config op for this. This isn't enough to address all vhost devices since
these do not get the features until FEATURES_OK, however it looks like
the affected devices actually never handled the endianness for legacy
mode correctly, so at least that's not a regression.

No devices except virtio net and virtio blk seem to be affected.

Long term the right thing to do is to fix the hypervisors.

Cc: <stable@vger.kernel.org> #v4.11
Signed-off-by: Halil Pasic <pasic@linux.ibm.com>
Fixes: 82e89ea077 ("virtio-blk: Add validation for block size in config space")
Fixes: fe36cbe067 ("virtio_net: clear MTU when out of range")
Reported-by: markver@us.ibm.com
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Link: https://lore.kernel.org/r/20211011053921.1198936-1-pasic@linux.ibm.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2021-10-20 10:42:04 +02:00
arch s390: fix strrchr() implementation 2021-10-20 10:42:03 +02:00
block blk-throttle: fix UAF by deleteing timer in blk_throtl_exit() 2021-09-26 13:37:30 +02:00
certs certs: Trigger creation of RSA module signing key if it's not an RSA key 2021-09-22 11:45:19 +02:00
crypto crypto: shash - avoid comparing pointers to exported functions under CFI 2021-07-20 16:17:32 +02:00
Documentation dt-bindings: mtd: gpmc: Fix the ECC bytes vs. OOB bytes equation 2021-09-22 11:45:34 +02:00
drivers virtio: write back F_VERSION_1 before validate 2021-10-20 10:42:04 +02:00
firmware Fix built-in early-load Intel microcode alignment 2020-01-23 08:20:30 +01:00
fs btrfs: check for error when looking up inode during dir entry replay 2021-10-20 10:42:03 +02:00
include sched: Always inline is_percpu_thread() 2021-10-17 10:08:34 +02:00
init pid: take a reference when initializing cad_pid 2021-06-10 12:43:51 +02:00
ipc ipc/util.c: sysvipc_find_ipc() incorrectly updates position index 2020-05-20 08:17:07 +02:00
kernel bpf: Fix integer overflow in prealloc_elems_and_freelist() 2021-10-17 10:08:32 +02:00
lib bpf: add also cbpf long jump test cases with heavy expansion 2021-10-17 10:08:32 +02:00
mm mm/memory_hotplug: use "unsigned long" for PFN in zone_for_pfn_range() 2021-09-22 11:45:34 +02:00
net mac80211: Drop frames from invalid MAC address in ad-hoc mode 2021-10-17 10:08:34 +02:00
samples samples/bpf: Fix the error return code of xdp_redirect's main() 2021-07-20 16:17:37 +02:00
scripts scripts/tracing: fix the bug that can't parse raw_trace_func 2021-08-15 13:03:31 +02:00
security apparmor: remove duplicate macro list_entry_is_head() 2021-09-26 13:37:28 +02:00
sound ALSA: seq: Fix a potential UAF by wrong private_free call order 2021-10-20 10:42:02 +02:00
tools usb: testusb: Fix for showing the connection speed 2021-10-09 14:09:46 +02:00
usr initramfs: restore default compression behavior 2020-04-13 10:34:19 +02:00
virt KVM: Use kvm_pfn_t for local PFN variable in hva_to_pfn_remapped() 2021-08-08 08:53:29 +02:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore kbuild: rpm-pkg: keep spec file until make mrproper 2018-02-13 10:19:46 +01:00
.mailmap .mailmap: Add Maciej W. Rozycki's Imagination e-mail address 2017-11-10 12:16:15 -08:00
COPYING
CREDITS MAINTAINERS: update TPM driver infrastructure changes 2017-11-09 17:58:40 -08:00
Kbuild License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
Kconfig License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
MAINTAINERS MAINTAINERS: Update drm/i915 bug filing URL 2020-02-28 16:36:12 +01:00
Makefile stable: clamp SUBLEVEL in 4.14 2021-10-20 10:42:02 +02:00
README README: add a new README file, pointing to the Documentation/ 2016-10-24 08:12:35 -02:00

README 

Linux kernel
============

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.