Linux Weekly News

The kmap() interface in the kernel is a bit of a strange beast. It only exists to overcome the virtual addressing limitations of 32-bit CPUs, but it affects code across the kernel and has side effects on 64-bit machines as well. A recent discussion on the handling of preemption within the kernel identified a number of problems in need of attention, one of which was the kmap() API. Now, an extension to this API called kmap_local() is being proposed to address some of the problems; it signals another step in the kernel community's slow move away from supporting 32-bit machines as first-class citizens.

Security updates have been issued by Debian (sddm and wordpress), Fedora (blueman, chromium, pngcheck, and salt), openSUSE (chromium, salt, tiff, tigervnc, tmux, tomcat, transfig, and xen), Oracle (freetype, kernel, libX11, thunderbird, and xorg-x11-server), SUSE (bluez, ImageMagick, java-1_8_0-openjdk, rmt-server, salt, and u-boot), and Ubuntu (dom4j, firefox, netqmail, phpldapadmin, and tmux).

The scp command, which uses the SSH protocol to copy files between machines, is deeply wired into the fingers of many Linux users and developers — doubly so for those of us who still think of it as a more secure replacement for rcp. Many users may be surprised to learn, though, that the resemblance to rcp goes beyond the name; much of the underlying protocol is the same as well. That protocol is showing its age, and the OpenSSH community has considered it deprecated for a while. Replacing scp in a way that keeps users happy may not be an easy task, though.

Four new stable kernels have been released: 5.9.5, 5.4.75, 4.19.155, and 4.14.204. They are fairly large updates with lots of important fixes throughout the kernel tree; users should upgrade.

Update: 5.9.6 has been released to fix a build problem with 5.9.5: "if 5.9.5 built properly for you, wonderful, no need to upgrade".

Security updates have been issued by Debian (bouncycastle, gdm3, and libonig), Fedora (arpwatch, thunderbird, and trousers), openSUSE (chromium, gn), Red Hat (freetype, libX11, thunderbird, and xorg-x11-server), and SUSE (ImageMagick, java-11-openjdk, salt, and wireshark).

The LWN.net Weekly Edition for November 5, 2020 is available.

At this year's (virtual) Open Source Summit Europe, Oleg Fiksel gave an overview talk on the Matrix decentralized, secure communication network project. Matrix has been seeing increasing adoption recently, he said, including by governments (beyond France, which we already reported on in an article on a FOSDEM 2019 talk) and other organizations. It also aims to bridge all of the different chat mechanisms that people are using in order to provide a unified interface for all of them.

Greg Kroah-Hartman has released stable kernel 5.9.4. "This is only a bugfix for the 5.9.3 kernel release which had some problems with some symlinks for the powerpc selftests." If you did not have any issues with 5.9.3 there is no need to upgrade.

Security updates have been issued by Arch Linux (chromium and firefox), Fedora (nss), openSUSE (pacemaker), Red Hat (bind, binutils, bluez, cloud-init, container-tools:rhel8, cryptsetup, cups, curl, cyrus-imapd, cyrus-sasl, dovecot, dpdk, edk2, evolution, expat, file-roller, fontforge, freeradius:3.0, freerdp and vinagre, freetype, frr, gd, glibc, GNOME, gnome-software and fwupd, gnupg2, grafana, httpd:2.4, idm:DL1 and idm:client, kernel, kernel-rt, libarchive, libexif, libgcrypt, libldb, libpcap, librabbitmq, libreoffice, librsvg2, libsolv, libssh, libtiff, libvpx, libX11, libxml2, libxslt, mailman:2.1, mingw-expat, nodejs:12, oddjob, oniguruma, opensc, openssl, openwsman, pcre2, pki-core:10.6 and pki-deps:10.6, poppler, prometheus-jmx-exporter, python-pip, python27:2.7, python3, python38:3.8, qt5-qtbase and qt5-qtwebsockets, resource-agents, SDL, spamassassin, sqlite, squid:4, subversion:1.10, sysstat, systemd, targetcli, tcpdump, thunderbird, varnish:6, vim, and virt:rhel and virt-devel:rhel), SUSE (apache-commons-httpclient, gnome-settings-daemon, gnome-shell, kernel, libvirt, opensc, ovmf, python, rmt-server, and sane-backends), and Ubuntu (accountsservice, gdm3, libytnef, python-cryptography, and spice-vdagent).

Pluto is a new computational notebook for the Julia programming language. Computational notebooks are a way to program inside of a web browser, storing code, annotations, and output, including graphics, in a single place. They became popular with the advent of the Jupyter notebook, which originally targeted Julia, Python, and R—the names got mashed together to make the word "Jupyter".

Kernel.org manager Konstantin Ryabitsev describes the Git signed-push functionality, which is now supported by the kernel.org system. "To help hedge against this problem, git provides developers a way to sign their actual pushes, as a means to attest 'yes, I actually did intend to push these commits into this ref in this repository on this server, and here's my PGP signature to prove it.'" Among other things, these signatures can be preserved in a commit transparency log, which is also now provided by kernel.org.

Alyssa Rosenzweig reports on the progress of the Panfrost driver. "Since our previous update on Panfrost, the open source stack for Arm's Mali Midgard and Bifrost GPUs, we've focused on taking our driver from its reverse-engineered origins on Midgard to a mature stack. We've overhauled both the Gallium driver and the backend compiler, and as a result, Mesa 20.3 -- scheduled for release at the end-of-the-month -- will feature some Bifrost support out-of-the-box."

Security updates have been issued by Debian (blueman and wordpress), Fedora (fastd, kernel, and samba), Gentoo (bluez, fossil, kpmcore, libssh, and opendmarc), openSUSE (claws-mail and icinga2), and Ubuntu (blueman).

For those who are following along with Linus Walleij's detailed writeup of how the 32-bit Arm bootstrap process works, he has posted two new installments (part 1, part 2) on what happens once virtual memory is enabled. "This init task is task 0. It is not identical to task 1, which will be the init process. That is a completely different task that gets forked in userspace later on. This task is only about providing context for the kernel itself, and a point for the first task (task 1) to fork from. The kernel is very dependent on context as we shall see, and that is why its thread/task information and even the stack pointer for this 'task zero' is hardcoded into the kernel like this. This 'zero task' does not even appear to userspace if you type ps aux, it is hidden inside the kernel."

Overclocking the processor — running it above its specified maximum frequency to increase performance — is a familiar operation for many readers. Sometimes, however, it is necessary to go the other direction and decrease a processor's operating power point by lowering its voltage to avoid overheating. Recently, Jason Donenfeld submitted a short patch removing a warning emitted by the kernel when user space accesses special processor registers that allow this "undervolting" on x86 processors. It caused a long discussion that might result in a kernel interface to allow users to safely control their processor's voltage.

The net today carries the sad news that Dan Kohn has passed away. Among other things, Dan played a huge role in the establishment of the Linux Foundation and a number of its initiatives, including the Cloud Native Computing Foundation and LF Public Health. He will be missed.

Security updates have been issued by Debian (cimg, junit4, kernel, openldap, qtsvg-opensource-src, spice, spice-gtk, tzdata, and wireshark), Fedora (firefox, java-1.8.0-openjdk, java-11-openjdk, and thunderbird), openSUSE (apache2, binutils, libvirt, lout, pacemaker, pagure, phpMyAdmin, samba, sane-backends, singularity, spice, spice-gtk, thunderbird, nspr, tomcat, virt-bootstrap, and xen), SUSE (graphviz, liblouis, and samba), and Ubuntu (samba).

The second 5.10 kernel prepatch is out for testing. "Despite the size, I don't get the feeling that there's anything really odd going on, and so far the release seems to be going smoothly. But please test, that's how we find problems."

The 5.9.3, 5.8.18, and 5.4.74 stable kernel updates are out; each contains another set of important fixes.

Linux distributors are in the business of integrating software from multiple sources, packaging the result, and making it available to their users. It has long been true that some projects are easier to package than others. The Debian technical committee (TC) is currently being asked to make a decision in a dispute over how an especially hard-to-package project — Kubernetes — should be handled. Regardless of the eventual outcome, this disagreement clearly shows how the packaging model used by Linux distributors is increasingly mismatched to how software is often developed in the 2020s; what should replace that model is rather less clear, though.