linux.git/include/linux/random.h, branch v6.1

prandom: remove unused functions

2022-10-11T23:42:58+00:00

With no callers left of prandom_u32() and prandom_bytes(), as well as
get_random_int(), remove these deprecated wrappers, in favor of
get_random_u32() and get_random_bytes().

Reviewed-by: Greg Kroah-Hartman 
Reviewed-by: Kees Cook 
Reviewed-by: Yury Norov 
Acked-by: Jakub Kicinski 
Signed-off-by: Jason A. Donenfeld

random: clear new batches when bringing new CPUs online

2022-10-06T15:35:55+00:00

The commit that added the new get_random_{u8,u16}() functions neglected
to update the code that clears the batches when bringing up a new CPU.
It also forgot a few comments and helper defines, so add those in too.

Fixes: 585cd5fe9f73 ("random: add 8-bit and 16-bit batches")
Signed-off-by: Jason A. Donenfeld

random: add 8-bit and 16-bit batches

2022-09-29T19:37:27+00:00

There are numerous places in the kernel that would be sped up by having
smaller batches. Currently those callsites do `get_random_u32() & 0xff`
or similar. Since these are pretty spread out, and will require patches
to multiple different trees, let's get ahead of the curve and lay the
foundation for `get_random_u8()` and `get_random_u16()`, so that it's
then possible to start submitting conversion patches leisurely.

Signed-off-by: Jason A. Donenfeld

random: split initialization into early step and later step

2022-09-29T19:36:27+00:00

The full RNG initialization relies on some timestamps, made possible
with initialization functions like time_init() and timekeeping_init().
However, these are only available rather late in initialization.
Meanwhile, other things, such as memory allocator functions, make use of
the RNG much earlier.

So split RNG initialization into two phases. We can provide arch
randomness very early on, and then later, after timekeeping and such are
available, initialize the rest.

This ensures that, for example, slabs are properly randomized if RDRAND
is available. Without this, CONFIG_SLAB_FREELIST_RANDOM=y loses a degree
of its security, because its random seed is potentially deterministic,
since it hasn't yet incorporated RDRAND. It also makes it possible to
use a better seed in kfence, which currently relies on only the cycle
counter.

Another positive consequence is that on systems with RDRAND, running
with CONFIG_WARN_ALL_UNSEEDED_RANDOM=y results in no warnings at all.

One subtle side effect of this change is that on systems with no RDRAND,
RDTSC is now only queried by random_init() once, committing the moment
of the function call, instead of multiple times as before. This is
intentional, as the multiple RDTSCs in a loop before weren't
accomplishing very much, with jitter being better provided by
try_to_generate_entropy(). Plus, filling blocks with RDTSC is still
being done in extract_entropy(), which is necessarily called before
random bytes are served anyway.

Cc: Andrew Morton 
Reviewed-by: Kees Cook 
Reviewed-by: Dominik Brodowski 
Signed-off-by: Jason A. Donenfeld

random: handle archrandom with multiple longs

2022-07-25T11:26:14+00:00

The archrandom interface was originally designed for x86, which supplies
RDRAND/RDSEED for receiving random words into registers, resulting in
one function to generate an int and another to generate a long. However,
other architectures don't follow this.

On arm64, the SMCCC TRNG interface can return between one and three
longs. On s390, the CPACF TRNG interface can return arbitrary amounts,
with four longs having the same cost as one. On UML, the os_getrandom()
interface can return arbitrary amounts.

So change the api signature to take a "max_longs" parameter designating
the maximum number of longs requested, and then return the number of
longs generated.

Since callers need to check this return value and loop anyway, each arch
implementation does not bother implementing its own loop to try again to
fill the maximum number of longs. Additionally, all existing callers
pass in a constant max_longs parameter. Taken together, these two things
mean that the codegen doesn't really change much for one-word-at-a-time
platforms, while performance is greatly improved on platforms such as
s390.

Acked-by: Heiko Carstens 
Acked-by: Catalin Marinas 
Acked-by: Mark Rutland 
Acked-by: Michael Ellerman 
Acked-by: Borislav Petkov 
Signed-off-by: Jason A. Donenfeld

random: remove CONFIG_ARCH_RANDOM

2022-07-18T13:03:37+00:00

When RDRAND was introduced, there was much discussion on whether it
should be trusted and how the kernel should handle that. Initially, two
mechanisms cropped up, CONFIG_ARCH_RANDOM, a compile time switch, and
"nordrand", a boot-time switch.

Later the thinking evolved. With a properly designed RNG, using RDRAND
values alone won't harm anything, even if the outputs are malicious.
Rather, the issue is whether those values are being *trusted* to be good
or not. And so a new set of options were introduced as the real
ones that people use -- CONFIG_RANDOM_TRUST_CPU and "random.trust_cpu".
With these options, RDRAND is used, but it's not always credited. So in
the worst case, it does nothing, and in the best case, maybe it helps.

Along the way, CONFIG_ARCH_RANDOM's meaning got sort of pulled into the
center and became something certain platforms force-select.

The old options don't really help with much, and it's a bit odd to have
special handling for these instructions when the kernel can deal fine
with the existence or untrusted existence or broken existence or
non-existence of that CPU capability.

Simplify the situation by removing CONFIG_ARCH_RANDOM and using the
ordinary asm-generic fallback pattern instead, keeping the two options
that are actually used. For now it leaves "nordrand" for now, as the
removal of that will take a different route.

Acked-by: Michael Ellerman 
Acked-by: Catalin Marinas 
Acked-by: Borislav Petkov 
Acked-by: Heiko Carstens 
Acked-by: Greg Kroah-Hartman 
Signed-off-by: Jason A. Donenfeld

random: remove rng_has_arch_random()

2022-06-10T09:29:48+00:00

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: mark bootloader randomness code as __init

2022-06-10T09:28:16+00:00

add_bootloader_randomness() and the variables it touches are only used
during __init and not after, so mark these as __init. At the same time,
unexport this, since it's only called by other __init code that's
built-in.

Cc: stable@vger.kernel.org
Fixes: 428826f5358c ("fdt: add support for rng-seed")
Signed-off-by: Jason A. Donenfeld

random: move randomize_page() into mm where it belongs

2022-05-19T14:54:15+00:00

randomize_page is an mm function. It is documented like one. It contains
the history of one. It has the naming convention of one. It looks
just like another very similar function in mm, randomize_stack_top().
And it has always been maintained and updated by mm people. There is no
need for it to be in random.c. In the "which shape does not look like
the other ones" test, pointing to randomize_page() is correct.

So move randomize_page() into mm/util.c, right next to the similar
randomize_stack_top() function.

This commit contains no actual code changes.

Cc: Andrew Morton 
Signed-off-by: Jason A. Donenfeld

random: remove mostly unused async readiness notifier

2022-05-19T14:54:15+00:00

The register_random_ready_notifier() notifier is somewhat complicated,
and was already recently rewritten to use notifier blocks. It is only
used now by one consumer in the kernel, vsprintf.c, for which the async
mechanism is really overly complex for what it actually needs. This
commit removes register_random_ready_notifier() and unregister_random_
ready_notifier(), because it just adds complication with little utility,
and changes vsprintf.c to just check on `!rng_is_initialized() &&
!rng_has_arch_random()`, which will eventually be true. Performance-
wise, that code was already using a static branch, so there's basically
no overhead at all to this change.

Cc: Steven Rostedt 
Cc: Sergey Senozhatsky 
Acked-by: Petr Mladek  # for vsprintf.c
Reviewed-by: Petr Mladek 
Signed-off-by: Jason A. Donenfeld