kernel.git/drivers/char/Kconfig, branch linux-5.4.y

random: credit cpu and bootloader seeds by default

2022-06-22T12:11:21Z

[ 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

2022-06-22T12:11:13Z

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

Merge tag 'please-pull-ia64_for_5.4' of git://git.kernel.org/pub/scm/linux/kernel/git/aegl/linux

2019-09-16T22:32:01Z

Pull ia64 updates from Tony Luck: "The big change here is removal of support for SGI Altix" * tag 'please-pull-ia64_for_5.4' of git://git.kernel.org/pub/scm/linux/kernel/git/aegl/linux: (33 commits) genirq: remove the is_affinity_mask_valid hook ia64: remove CONFIG_SWIOTLB ifdefs ia64: remove support for machvecs ia64: move the screen_info setup to common code ia64: move the ROOT_DEV setup to common code ia64: rework iommu probing ia64: remove the unused sn_coherency_id symbol ia64: remove the SGI UV simulator support ia64: remove the zx1 swiotlb machvec ia64: remove CONFIG_ACPI ifdefs ia64: remove CONFIG_PCI ifdefs ia64: remove the hpsim platform ia64: remove now unused machvec indirections ia64: remove support for the SGI SN2 platform drivers: remove the SGI SN2 IOC4 base support drivers: remove the SGI SN2 IOC3 base support qla2xxx: remove SGI SN2 support qla1280: remove SGI SN2 support misc/sgi-xp: remove SGI SN2 support char/mspec: remove SGI SN2 support ...

fdt: add support for rng-seed

2019-08-23T15:39:26Z

Introducing a chosen node, rng-seed, which is an entropy that can be passed to kernel called very early to increase initial device randomness. Bootloader should provide this entropy and the value is read from /chosen/rng-seed in DT. Obtain of_fdt_crc32 for CRC check after early_init_dt_scan_nodes(), since early_init_dt_scan_chosen() would modify fdt to erase rng-seed. Add a new interface add_bootloader_randomness() for rng-seed use case. Depends on whether the seed is trustworthy, rng seed would be passed to add_hwgenerator_randomness(). Otherwise it would be passed to add_device_randomness(). Decision is controlled by kernel config RANDOM_TRUST_BOOTLOADER. Signed-off-by: Hsin-Yi Wang Reviewed-by: Stephen Boyd Reviewed-by: Rob Herring Reviewed-by: Theodore Ts'o # drivers/char/random.c Signed-off-by: Will Deacon

char: remove the SGI tiocx/mbcs driver

2019-08-16T18:33:56Z

The SGI SN2 support is about to be removed. Remove this driver that depends on the SN2 support. Signed-off-by: Christoph Hellwig Link: https://lkml.kernel.org/r/20190813072514.23299-3-hch@lst.de Signed-off-by: Tony Luck

char: remove the SGI snsc driver

2019-08-16T18:33:56Z

docs: admin-guide: add a series of orphaned documents

2019-07-15T14:03:02Z

There are lots of documents that belong to the admin-guide but are on random places (most under Documentation root dir). Move them to the admin guide. Signed-off-by: Mauro Carvalho Chehab Acked-by: Alexandre Belloni Acked-by: Bartlomiej Zolnierkiewicz

docs: admin-guide: add laptops documentation

2019-07-15T14:03:01Z

The docs under Documentation/laptops contain users specific information. Signed-off-by: Mauro Carvalho Chehab Acked-by: Andy Shevchenko

docs: laptops: convert to ReST

2019-07-15T12:20:25Z

Rename the laptops documentation files to ReST, add an index for them and adjust in order to produce a nice html output via the Sphinx build system. At its new index.rst, let's add a :orphan: while this is not linked to the main index.rst file, in order to avoid build warnings. Signed-off-by: Mauro Carvalho Chehab Acked-by: Andy Shevchenko

tty: mark Siemens R3964 line discipline as BROKEN

2019-04-05T15:56:44Z

The n_r3964 line discipline driver was written in a different time, when SMP machines were rare, and users were trusted to do the right thing. Since then, the world has moved on but not this code, it has stayed rooted in the past with its lovely hand-crafted list structures and loads of "interesting" race conditions all over the place. After attempting to clean up most of the issues, I just gave up and am now marking the driver as BROKEN so that hopefully someone who has this hardware will show up out of the woodwork (I know you are out there!) and will help with debugging a raft of changes that I had laying around for the code, but was too afraid to commit as odds are they would break things. Many thanks to Jann and Linus for pointing out the initial problems in this codebase, as well as many reviews of my attempts to fix the issues. It was a case of whack-a-mole, and as you can see, the mole won. Reported-by: Jann Horn Signed-off-by: Greg Kroah-Hartman Signed-off-by: Linus Torvalds