kernel/linux.git/drivers/char/Kconfig, branch v5.10.257

random: credit cpu and bootloader seeds by default

2022-06-22T12:13:15+00:00

[ Upstream commit 846bb97e131d7938847963cca00657c995b1fce1 ] This commit changes the default Kconfig values of RANDOM_TRUST_CPU and RANDOM_TRUST_BOOTLOADER to be Y by default. It does not change any existing configs or change any kernel behavior. The reason for this is several fold. As background, I recently had an email thread with the kernel maintainers of Fedora/RHEL, Debian, Ubuntu, Gentoo, Arch, NixOS, Alpine, SUSE, and Void as recipients. I noted that some distros trust RDRAND, some trust EFI, and some trust both, and I asked why or why not. There wasn't really much of a "debate" but rather an interesting discussion of what the historical reasons have been for this, and it came up that some distros just missed the introduction of the bootloader Kconfig knob, while another didn't want to enable it until there was a boot time switch to turn it off for more concerned users (which has since been added). The result of the rather uneventful discussion is that every major Linux distro enables these two options by default. While I didn't have really too strong of an opinion going into this thread -- and I mostly wanted to learn what the distros' thinking was one way or another -- ultimately I think their choice was a decent enough one for a default option (which can be disabled at boot time). I'll try to summarize the pros and cons: Pros: - The RNG machinery gets initialized super quickly, and there's no messing around with subsequent blocking behavior. - The bootloader mechanism is used by kexec in order for the prior kernel to initialize the RNG of the next kernel, which increases the entropy available to early boot daemons of the next kernel. - Previous objections related to backdoors centered around Dual_EC_DRBG-like kleptographic systems, in which observing some amount of the output stream enables an adversary holding the right key to determine the entire output stream. This used to be a partially justified concern, because RDRAND output was mixed into the output stream in varying ways, some of which may have lacked pre-image resistance (e.g. XOR or an LFSR). But this is no longer the case. Now, all usage of RDRAND and bootloader seeds go through a cryptographic hash function. This means that the CPU would have to compute a hash pre-image, which is not considered to be feasible (otherwise the hash function would be terribly broken). - More generally, if the CPU is backdoored, the RNG is probably not the realistic vector of choice for an attacker. - These CPU or bootloader seeds are far from being the only source of entropy. Rather, there is generally a pretty huge amount of entropy, not all of which is credited, especially on CPUs that support instructions like RDRAND. In other words, assuming RDRAND outputs all zeros, an attacker would *still* have to accurately model every single other entropy source also in use. - The RNG now reseeds itself quite rapidly during boot, starting at 2 seconds, then 4, then 8, then 16, and so forth, so that other sources of entropy get used without much delay. - Paranoid users can set random.trust_{cpu,bootloader}=no in the kernel command line, and paranoid system builders can set the Kconfig options to N, so there's no reduction or restriction of optionality. - It's a practical default. - All the distros have it set this way. Microsoft and Apple trust it too. Bandwagon. Cons: - RDRAND *could* still be backdoored with something like a fixed key or limited space serial number seed or another indexable scheme like that. (However, it's hard to imagine threat models where the CPU is backdoored like this, yet people are still okay making *any* computations with it or connecting it to networks, etc.) - RDRAND *could* be defective, rather than backdoored, and produce garbage that is in one way or another insufficient for crypto. - Suggesting a *reduction* in paranoia, as this commit effectively does, may cause some to question my personal integrity as a "security person". - Bootloader seeds and RDRAND are generally very difficult if not all together impossible to audit. Keep in mind that this doesn't actually change any behavior. This is just a change in the default Kconfig value. The distros already are shipping kernels that set things this way. Ard made an additional argument in [1]: We're at the mercy of firmware and micro-architecture anyway, given that we are also relying on it to ensure that every instruction in the kernel's executable image has been faithfully copied to memory, and that the CPU implements those instructions as documented. So I don't think firmware or ISA bugs related to RNGs deserve special treatment - if they are broken, we should quirk around them like we usually do. So enabling these by default is a step in the right direction IMHO. In [2], Phil pointed out that having this disabled masked a bug that CI otherwise would have caught: A clean 5.15.45 boots cleanly, whereas a downstream kernel shows the static key warning (but it does go on to boot). The significant difference is that our defconfigs set CONFIG_RANDOM_TRUST_BOOTLOADER=y defining that on top of multi_v7_defconfig demonstrates the issue on a clean 5.15.45. Conversely, not setting that option in a downstream kernel build avoids the warning [1] https://lore.kernel.org/lkml/CAMj1kXGi+ieviFjXv9zQBSaGyyzeGW_VpMpTLJK8PJb2QHEQ-w@mail.gmail.com/ [2] https://lore.kernel.org/lkml/c47c42e3-1d56-5859-a6ad-976a1a3381c6@raspberrypi.com/ Cc: Theodore Ts'o Reviewed-by: Ard Biesheuvel Signed-off-by: Jason A. Donenfeld Signed-off-by: Sasha Levin

random: treat bootloader trust toggle the same way as cpu trust toggle

2022-05-30T07:33:38+00:00

commit d97c68d178fbf8aaaf21b69b446f2dfb13909316 upstream. If CONFIG_RANDOM_TRUST_CPU is set, the RNG initializes using RDRAND. But, the user can disable (or enable) this behavior by setting `random.trust_cpu=0/1` on the kernel command line. This allows system builders to do reasonable things while avoiding howls from tinfoil hatters. (Or vice versa.) CONFIG_RANDOM_TRUST_BOOTLOADER is basically the same thing, but regards the seed passed via EFI or device tree, which might come from RDRAND or a TPM or somewhere else. In order to allow distros to more easily enable this while avoiding those same howls (or vice versa), this commit adds the corresponding `random.trust_bootloader=0/1` toggle. Cc: Theodore Ts'o Cc: Graham Christensen Reviewed-by: Ard Biesheuvel Reviewed-by: Dominik Brodowski Link: https://github.com/NixOS/nixpkgs/pull/165355 Signed-off-by: Jason A. Donenfeld Signed-off-by: Greg Kroah-Hartman

char: virtio: Select VIRTIO from VIRTIO_CONSOLE.

2020-09-07T12:32:40+00:00

Make it possible to have virtio console built-in when other virtio drivers are modular. Signed-off-by: Michal Suchanek Reviewed-by: Amit Shah Link: https://lore.kernel.org/r/20200831165850.26163-1-msuchanek@suse.de Signed-off-by: Greg Kroah-Hartman

char: Replace HTTP links with HTTPS ones

2020-07-23T07:44:15+00:00

Rationale: Reduces attack surface on kernel devs opening the links for MITM as HTTPS traffic is much harder to manipulate. Deterministic algorithm: For each file: If not .svg: For each line: If doesn't contain `\bxmlns\b`: For each link, `\bhttp://[^# \t\r\n]*(?:\w|/)`: If neither `\bgnu\.org/license`, nor `\bmozilla\.org/MPL\b`: If both the HTTP and HTTPS versions return 200 OK and serve the same content: Replace HTTP with HTTPS. Signed-off-by: Alexander A. Klimov Link: https://lore.kernel.org/r/20200713104453.33414-1-grandmaster@al2klimov.de Signed-off-by: Greg Kroah-Hartman

treewide: replace '---help---' in Kconfig files with 'help'

2020-06-13T16:57:21+00:00

Since commit 84af7a6194e4 ("checkpatch: kconfig: prefer 'help' over '---help---'"), the number of '---help---' has been gradually decreasing, but there are still more than 2400 instances. This commit finishes the conversion. While I touched the lines, I also fixed the indentation. There are a variety of indentation styles found. a) 4 spaces + '---help---' b) 7 spaces + '---help---' c) 8 spaces + '---help---' d) 1 space + 1 tab + '---help---' e) 1 tab + '---help---' (correct indentation) f) 1 tab + 1 space + '---help---' g) 1 tab + 2 spaces + '---help---' In order to convert all of them to 1 tab + 'help', I ran the following commend: $ find . -name 'Kconfig*' | xargs sed -i 's/^[[:space:]]*---help---/\thelp/' Signed-off-by: Masahiro Yamada

powerpc: Remove Xilinx PPC405/PPC440 support

2020-05-28T13:24:34+00:00

The latest Xilinx design tools called ISE and EDK has been released in October 2013. New tool doesn't support any PPC405/PPC440 new designs. These platforms are no longer supported and tested. PowerPC 405/440 port is orphan from 2013 by commit cdeb89943bfc ("MAINTAINERS: Fix incorrect status tag") and commit 19624236cce1 ("MAINTAINERS: Update Grant's email address and maintainership") that's why it is time to remove the support fot these platforms. Signed-off-by: Michal Simek Signed-off-by: Christophe Leroy Acked-by: Arnd Bergmann Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/8c593895e2cb57d232d85ce4d8c3a1aa7f0869cc.1590079968.git.christophe.leroy@csgroup.eu

Merge tag 'random_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/random

2020-04-05T17:59:18+00:00

Pull /dev/random updates from Ted Ts'o: - Improve getrandom and /dev/random's support for those arm64 architecture variants that have RNG instructions. - Use batched output from CRNG instead of CPU's RNG instructions for better performance. - Miscellaneous bug fixes. * tag 'random_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/random: random: avoid warnings for !CONFIG_NUMA builds random: fix data races at timer_rand_state random: always use batched entropy for get_random_u{32,64} random: Make RANDOM_TRUST_CPU depend on ARCH_RANDOM arm64: add credited/trusted RNG support random: add arch_get_random_*long_early() random: split primary/secondary crng init paths

rtc/alpha: remove legacy rtc driver

2020-03-19T06:41:02+00:00

The old drivers/char/rtc.c driver was originally the implementation for x86 PCs but got subsequently replaced by the rtc class driver on all architectures except alpha. Move alpha over to the portable driver and remove the old one for good. The CONFIG_JS_RTC option was only ever used on SPARC32 but has not been available for many years, this was used to build the same rtc driver with a different module name. Cc: Richard Henderson Cc: Ivan Kokshaysky Cc: Matt Turner Cc: linux-alpha@vger.kernel.org Cc: Paul Gortmaker Signed-off-by: Arnd Bergmann Signed-off-by: Alexandre Belloni Link: https://lore.kernel.org/r/20200226224322.187960-2-alexandre.belloni@bootlin.com Signed-off-by: Greg Kroah-Hartman

rtc/ia64: remove legacy efirtc driver

2020-03-19T06:41:02+00:00

There are two EFI RTC drivers, the original drivers/char/efirtc.c driver and the more modern drivers/rtc/rtc-efi.c. Both implement the same interface, but the new one does so in a more portable way. Move everything over to that one and remove the old one. Cc: linux-ia64@vger.kernel.org Cc: Fenghua Yu Cc: Tony Luck Cc: Stephane Eranian Signed-off-by: Arnd Bergmann Signed-off-by: Alexandre Belloni Link: https://lore.kernel.org/r/20200226224322.187960-1-alexandre.belloni@bootlin.com Signed-off-by: Greg Kroah-Hartman

tty: source all tty Kconfig files in one place

2020-03-12T16:17:30+00:00

'source' (include) all of the tty/*/Kconfig files from drivers/tty/Kconfig instead of from drivers/char/Kconfig. This consolidates them both in source code and in menu presentation to the user. Move hvc/Kconfig and serial/Kconfig 'source' lines into the if TTY/endif block and remove the if TTY/endif blocks from those 2 files. Cc: linux-serial@vger.kernel.org Cc: Jiri Slaby Cc: Greg Kroah-Hartman Cc: Arnd Bergmann Suggested-by: Jiri Slaby Suggested-by: Arnd Bergmann Acked-by: Arnd Bergmann Signed-off-by: Randy Dunlap Link: https://lore.kernel.org/r/20200311225736.32147-3-rdunlap@infradead.org Signed-off-by: Greg Kroah-Hartman