linux-dev/drivers/char, branch linus/master

random: update comment from copy_to_user() -> copy_to_iter()

2022-06-20T09:06:17Z

This comment wasn't updated when we moved from read() to read_iter(), so this patch makes the trivial fix. Fixes: 1b388e7765f2 ("random: convert to using fops->read_iter()") Signed-off-by: Jason A. Donenfeld

random: quiet urandom warning ratelimit suppression message

2022-06-19T21:50:46Z

random.c ratelimits how much it warns about uninitialized urandom reads using __ratelimit(). When the RNG is finally initialized, it prints the number of missed messages due to ratelimiting. It has been this way since that functionality was introduced back in 2018. Recently, cc1e127bfa95 ("random: remove ratelimiting for in-kernel unseeded randomness") put a bit more stress on the urandom ratelimiting, which teased out a bug in the implementation. Specifically, when under pressure, __ratelimit() will print its own message and reset the count back to 0, making the final message at the end less useful. Secondly, it does so as a pr_warn(), which apparently is undesirable for people's CI. Fortunately, __ratelimit() has the RATELIMIT_MSG_ON_RELEASE flag exactly for this purpose, so we set the flag. Fixes: 4e00b339e264 ("random: rate limit unseeded randomness warnings") Cc: stable@vger.kernel.org Reported-by: Jon Hunter Reported-by: Ron Economos Tested-by: Ron Economos Signed-off-by: Jason A. Donenfeld

random: schedule mix_interrupt_randomness() less often

2022-06-19T21:50:45Z

It used to be that mix_interrupt_randomness() would credit 1 bit each time it ran, and so add_interrupt_randomness() would schedule mix() to run every 64 interrupts, a fairly arbitrary number, but nonetheless considered to be a decent enough conservative estimate. Since e3e33fc2ea7f ("random: do not use input pool from hard IRQs"), mix() is now able to credit multiple bits, depending on the number of calls to add(). This was done for reasons separate from this commit, but it has the nice side effect of enabling this patch to schedule mix() less often. Currently the rules are: a) Credit 1 bit for every 64 calls to add(). b) Schedule mix() once a second that add() is called. c) Schedule mix() once every 64 calls to add(). Rules (a) and (c) no longer need to be coupled. It's still important to have _some_ value in (c), so that we don't "over-saturate" the fast pool, but the once per second we get from rule (b) is a plenty enough baseline. So, by increasing the 64 in rule (c) to something larger, we avoid calling queue_work_on() as frequently during irq storms. This commit changes that 64 in rule (c) to be 1024, which means we schedule mix() 16 times less often. And it does *not* need to change the 64 in rule (a). Fixes: 58340f8e952b ("random: defer fast pool mixing to worker") Cc: stable@vger.kernel.org Cc: Dominik Brodowski Acked-by: Sebastian Andrzej Siewior Signed-off-by: Jason A. Donenfeld

Merge tag 'char-misc-5.19-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc

2022-06-17T14:58:39Z

Pull char/misc driver fixes from Greg KH: "Here are some small char/misc driver fixes for 5.19-rc3 that resolve some reported issues. They include: - mei driver fixes - comedi driver fix - rtsx build warning fix - fsl-mc-bus driver fix All of these have been in linux-next for a while with no reported issues" * tag 'char-misc-5.19-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc: eeprom: at25: Split reads into chunks and cap write size misc: atmel-ssc: Fix IRQ check in ssc_probe char: lp: remove redundant initialization of err

Merge tag 'random-5.19-rc2-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/crng/random

2022-06-12T17:33:38Z

Pull random number generator fixes from Jason Donenfeld: - A fix for a 5.19 regression for a case in which early device tree initializes the RNG, which flips a static branch. On most plaforms, jump labels aren't initialized until much later, so this caused splats. On a few mailing list threads, we cooked up easy fixes for arm64, arm32, and risc-v. But then things looked slightly more involved for xtensa, powerpc, arc, and mips. And at that point, when we're patching 7 architectures in a place before the console is even available, it seems like the cost/risk just wasn't worth it. So random.c works around it now by checking the already exported `static_key_initialized` boolean, as though somebody already ran into this issue in the past. I'm not super jazzed about that; it'd be prettier to not have to complicate downstream code. But I suppose it's practical. - A few small code nits and adding a missing __init annotation. - A change to the default config values to use the cpu and bootloader's seeds for initializing the RNG earlier. This brings them into line with what all the distros do (Fedora/RHEL, Debian, Ubuntu, Gentoo, Arch, NixOS, Alpine, SUSE, and Void... at least), and moreover will now give us test coverage in various test beds that might have caught the above device tree bug earlier. - A change to WireGuard CI's configuration to increase test coverage around the RNG. - A documentation comment fix to unrelated maintainerless CRC code that I was asked to take, I guess because it has to do with polynomials (which the RNG thankfully no longer uses). * tag 'random-5.19-rc2-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/crng/random: wireguard: selftests: use maximum cpu features and allow rng seeding random: remove rng_has_arch_random() random: credit cpu and bootloader seeds by default random: do not use jump labels before they are initialized random: account for arch randomness in bits random: mark bootloader randomness code as __init random: avoid checking crng_ready() twice in random_init() crc-itu-t: fix typo in CRC ITU-T polynomial comment

char: lp: remove redundant initialization of err

2022-06-10T13:29:50Z

err is getting assigned with an appropriate value before returning, hence this initialization is unnecessary. Signed-off-by: Shreenidhi Shedi Link: https://lore.kernel.org/r/20220603130040.601673-2-sshedi@vmware.com Signed-off-by: Greg Kroah-Hartman

random: remove rng_has_arch_random()

2022-06-10T09:29:48Z

With arch randomness being used by every distro and enabled in defconfigs, the distinction between rng_has_arch_random() and rng_is_initialized() is now rather small. In fact, the places where they differ are now places where paranoid users and system builders really don't want arch randomness to be used, in which case we should respect that choice, or places where arch randomness is known to be broken, in which case that choice is all the more important. So this commit just removes the function and its one user. Reviewed-by: Petr Mladek # for vsprintf.c Signed-off-by: Jason A. Donenfeld

random: credit cpu and bootloader seeds by default

2022-06-10T09:29:48Z

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

random: do not use jump labels before they are initialized

2022-06-10T09:29:48Z

Stephen reported that a static key warning splat appears during early boot on systems that credit randomness from device trees that contain an "rng-seed" property, because because setup_machine_fdt() is called before jump_label_init() during setup_arch(): static_key_enable_cpuslocked(): static key '0xffffffe51c6fcfc0' used before call to jump_label_init() WARNING: CPU: 0 PID: 0 at kernel/jump_label.c:166 static_key_enable_cpuslocked+0xb0/0xb8 Modules linked in: CPU: 0 PID: 0 Comm: swapper Not tainted 5.18.0+ #224 44b43e377bfc84bc99bb5ab885ff694984ee09ff pstate: 600001c9 (nZCv dAIF -PAN -UAO -TCO -DIT -SSBS BTYPE=--) pc : static_key_enable_cpuslocked+0xb0/0xb8 lr : static_key_enable_cpuslocked+0xb0/0xb8 sp : ffffffe51c393cf0 x29: ffffffe51c393cf0 x28: 000000008185054c x27: 00000000f1042f10 x26: 0000000000000000 x25: 00000000f10302b2 x24: 0000002513200000 x23: 0000002513200000 x22: ffffffe51c1c9000 x21: fffffffdfdc00000 x20: ffffffe51c2f0831 x19: ffffffe51c6fcfc0 x18: 00000000ffff1020 x17: 00000000e1e2ac90 x16: 00000000000000e0 x15: ffffffe51b710708 x14: 0000000000000066 x13: 0000000000000018 x12: 0000000000000000 x11: 0000000000000000 x10: 00000000ffffffff x9 : 0000000000000000 x8 : 0000000000000000 x7 : 61632065726f6665 x6 : 6220646573752027 x5 : ffffffe51c641d25 x4 : ffffffe51c13142c x3 : ffff0a00ffffff05 x2 : 40000000ffffe003 x1 : 00000000000001c0 x0 : 0000000000000065 Call trace: static_key_enable_cpuslocked+0xb0/0xb8 static_key_enable+0x2c/0x40 crng_set_ready+0x24/0x30 execute_in_process_context+0x80/0x90 _credit_init_bits+0x100/0x154 add_bootloader_randomness+0x64/0x78 early_init_dt_scan_chosen+0x140/0x184 early_init_dt_scan_nodes+0x28/0x4c early_init_dt_scan+0x40/0x44 setup_machine_fdt+0x7c/0x120 setup_arch+0x74/0x1d8 start_kernel+0x84/0x44c __primary_switched+0xc0/0xc8 ---[ end trace 0000000000000000 ]--- random: crng init done Machine model: Google Lazor (rev1 - 2) with LTE A trivial fix went in to address this on arm64, 73e2d827a501 ("arm64: Initialize jump labels before setup_machine_fdt()"). I wrote patches as well for arm32 and risc-v. But still patches are needed on xtensa, powerpc, arc, and mips. So that's 7 platforms where things aren't quite right. This sort of points to larger issues that might need a larger solution. Instead, this commit just defers setting the static branch until later in the boot process. random_init() is called after jump_label_init() has been called, and so is always a safe place from which to adjust the static branch. Fixes: f5bda35fba61 ("random: use static branch for crng_ready()") Reported-by: Stephen Boyd Reported-by: Phil Elwell Tested-by: Phil Elwell Reviewed-by: Ard Biesheuvel Cc: Catalin Marinas Cc: Russell King Cc: Arnd Bergmann Signed-off-by: Jason A. Donenfeld

random: account for arch randomness in bits

2022-06-10T09:29:42Z

Rather than accounting in bytes and multiplying (shifting), we can just account in bits and avoid the shift. The main motivation for this is there are other patches in flux that expand this code a bit, and avoiding the duplication of "* 8" everywhere makes things a bit clearer. Cc: stable@vger.kernel.org Fixes: 12e45a2a6308 ("random: credit architectural init the exact amount") Signed-off-by: Jason A. Donenfeld