const qualify the struct ctl_table argument in the proc_handler function
signatures. This is a prerequisite to moving the static ctl_table
structs into .rodata data which will ensure that proc_handler function
pointers cannot be modified.
This patch has been generated by the following coccinelle script:
```
virtual patch
@r1@
identifier ctl, write, buffer, lenp, ppos;
identifier func !~ "appldata_(timer|interval)_handler|sched_(rt|rr)_handler|rds_tcp_skbuf_handler|proc_sctp_do_(hmac_alg|rto_min|rto_max|udp_port|alpha_beta|auth|probe_interval)";
@@
int func(
- struct ctl_table *ctl
+ const struct ctl_table *ctl
,int write, void *buffer, size_t *lenp, loff_t *ppos);
@r2@
identifier func, ctl, write, buffer, lenp, ppos;
@@
int func(
- struct ctl_table *ctl
+ const struct ctl_table *ctl
,int write, void *buffer, size_t *lenp, loff_t *ppos)
{ ... }
@r3@
identifier func;
@@
int func(
- struct ctl_table *
+ const struct ctl_table *
,int , void *, size_t *, loff_t *);
@r4@
identifier func, ctl;
@@
int func(
- struct ctl_table *ctl
+ const struct ctl_table *ctl
,int , void *, size_t *, loff_t *);
@r5@
identifier func, write, buffer, lenp, ppos;
@@
int func(
- struct ctl_table *
+ const struct ctl_table *
,int write, void *buffer, size_t *lenp, loff_t *ppos);
```
* Code formatting was adjusted in xfs_sysctl.c to comply with code
conventions. The xfs_stats_clear_proc_handler,
xfs_panic_mask_proc_handler and xfs_deprecated_dointvec_minmax where
adjusted.
* The ctl_table argument in proc_watchdog_common was const qualified.
This is called from a proc_handler itself and is calling back into
another proc_handler, making it necessary to change it as part of the
proc_handler migration.
Co-developed-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Co-developed-by: Joel Granados <j.granados@samsung.com>
Signed-off-by: Joel Granados <j.granados@samsung.com>
Provide a generic C vDSO getrandom() implementation, which operates on
an opaque state returned by vgetrandom_alloc() and produces random bytes
the same way as getrandom(). This has the following API signature:
ssize_t vgetrandom(void *buffer, size_t len, unsigned int flags,
void *opaque_state, size_t opaque_len);
The return value and the first three arguments are the same as ordinary
getrandom(), while the last two arguments are a pointer to the opaque
allocated state and its size. Were all five arguments passed to the
getrandom() syscall, nothing different would happen, and the functions
would have the exact same behavior.
The actual vDSO RNG algorithm implemented is the same one implemented by
drivers/char/random.c, using the same fast-erasure techniques as that.
Should the in-kernel implementation change, so too will the vDSO one.
It requires an implementation of ChaCha20 that does not use any stack,
in order to maintain forward secrecy if a multi-threaded program forks
(though this does not account for a similar issue with SA_SIGINFO
copying registers to the stack), so this is left as an
architecture-specific fill-in. Stack-less ChaCha20 is an easy algorithm
to implement on a variety of architectures, so this shouldn't be too
onerous.
Initially, the state is keyless, and so the first call makes a
getrandom() syscall to generate that key, and then uses it for
subsequent calls. By keeping track of a generation counter, it knows
when its key is invalidated and it should fetch a new one using the
syscall. Later, more than just a generation counter might be used.
Since MADV_WIPEONFORK is set on the opaque state, the key and related
state is wiped during a fork(), so secrets don't roll over into new
processes, and the same state doesn't accidentally generate the same
random stream. The generation counter, as well, is always >0, so that
the 0 counter is a useful indication of a fork() or otherwise
uninitialized state.
If the kernel RNG is not yet initialized, then the vDSO always calls the
syscall, because that behavior cannot be emulated in userspace, but
fortunately that state is short lived and only during early boot. If it
has been initialized, then there is no need to inspect the `flags`
argument, because the behavior does not change post-initialization
regardless of the `flags` value.
Since the opaque state passed to it is mutated, vDSO getrandom() is not
reentrant, when used with the same opaque state, which libc should be
mindful of.
The function works over an opaque per-thread state of a particular size,
which must be marked VM_WIPEONFORK, VM_DONTDUMP, VM_NORESERVE, and
VM_DROPPABLE for proper operation. Over time, the nuances of these
allocations may change or grow or even differ based on architectural
features.
The opaque state passed to vDSO getrandom() must be allocated using the
mmap_flags and mmap_prot parameters provided by the vgetrandom_opaque_params
struct, which also contains the size of each state. That struct can be
obtained with a call to vgetrandom(NULL, 0, 0, ¶ms, ~0UL). Then,
libc can call mmap(2) and slice up the returned array into a state per
each thread, while ensuring that no single state straddles a page
boundary. Libc is expected to allocate a chunk of these on first use,
and then dole them out to threads as they're created, allocating more
when needed.
vDSO getrandom() provides the ability for userspace to generate random
bytes quickly and safely, and is intended to be integrated into libc's
thread management. As an illustrative example, the introduced code in
the vdso_test_getrandom self test later in this series might be used to
do the same outside of libc. In a libc the various pthread-isms are
expected to be elided into libc internals.
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
The entropy accounting changes a static key when the RNG has
initialized, since it only ever initializes once. Static key changes,
however, cannot be made from atomic context, so depending on where the
last creditable entropy comes from, the static key change might need to
be deferred to a worker.
Previously the code used the execute_in_process_context() helper
function, which accounts for whether or not the caller is
in_interrupt(). However, that doesn't account for the case where the
caller is actually in process context but is holding a spinlock.
This turned out to be the case with input_handle_event() in
drivers/input/input.c contributing entropy:
[<ffffffd613025ba0>] die+0xa8/0x2fc
[<ffffffd613027428>] bug_handler+0x44/0xec
[<ffffffd613016964>] brk_handler+0x90/0x144
[<ffffffd613041e58>] do_debug_exception+0xa0/0x148
[<ffffffd61400c208>] el1_dbg+0x60/0x7c
[<ffffffd61400c000>] el1h_64_sync_handler+0x38/0x90
[<ffffffd613011294>] el1h_64_sync+0x64/0x6c
[<ffffffd613102d88>] __might_resched+0x1fc/0x2e8
[<ffffffd613102b54>] __might_sleep+0x44/0x7c
[<ffffffd6130b6eac>] cpus_read_lock+0x1c/0xec
[<ffffffd6132c2820>] static_key_enable+0x14/0x38
[<ffffffd61400ac08>] crng_set_ready+0x14/0x28
[<ffffffd6130df4dc>] execute_in_process_context+0xb8/0xf8
[<ffffffd61400ab30>] _credit_init_bits+0x118/0x1dc
[<ffffffd6138580c8>] add_timer_randomness+0x264/0x270
[<ffffffd613857e54>] add_input_randomness+0x38/0x48
[<ffffffd613a80f94>] input_handle_event+0x2b8/0x490
[<ffffffd613a81310>] input_event+0x6c/0x98
According to Guoyong, it's not really possible to refactor the various
drivers to never hold a spinlock there. And in_atomic() isn't reliable.
So, rather than trying to be too fancy, just punt the change in the
static key to a workqueue always. There's basically no drawback of doing
this, as the code already needed to account for the static key not
changing immediately, and given that it's just an optimization, there's
not exactly a hurry to change the static key right away, so deferal is
fine.
Reported-by: Guoyong Wang <guoyong.wang@mediatek.com>
Cc: stable@vger.kernel.org
Fixes: f5bda35fba ("random: use static branch for crng_ready()")
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
This commit comes at the tail end of a greater effort to remove the
empty elements at the end of the ctl_table arrays (sentinels) which
will reduce the overall build time size of the kernel and run time
memory bloat by ~64 bytes per sentinel (further information Link :
https://lore.kernel.org/all/ZO5Yx5JFogGi%2FcBo@bombadil.infradead.org/)
Remove sentinel from impi_table and random_table
Signed-off-by: Joel Granados <j.granados@samsung.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
It turns out that commit 596ff4a09b ("cpumask: re-introduce
constant-sized cpumask optimizations") exposed a number of cases of
drivers not checking the result of "cpumask_next()" and friends
correctly.
The documented correct check for "no more cpus in the cpumask" is to
check for the result being equal or larger than the number of possible
CPU ids, exactly _because_ we've always done those constant-sized
cpumask scans using a widened type before. So the return value of a
cpumask scan should be checked with
if (cpu >= nr_cpu_ids)
...
because the cpumask scan did not necessarily stop exactly *at* that
maximum CPU id.
But a few cases ended up instead using checks like
if (cpu == nr_cpumask_bits)
...
which used that internal "widened" number of bits. And that used to
work pretty much by accident (ok, in this case "by accident" is simply
because it matched the historical internal implementation of the cpumask
scanning, so it was more of a "intentionally using implementation
details rather than an accident").
But the extended constant-sized optimizations then did that internal
implementation differently, and now that code that did things wrong but
matched the old implementation no longer worked at all.
Which then causes subsequent odd problems due to using what ends up
being an invalid CPU ID.
Most of these cases require either unusual hardware or special uses to
hit, but the random.c one triggers quite easily.
All you really need is to have a sufficiently small CONFIG_NR_CPUS value
for the bit scanning optimization to be triggered, but not enough CPUs
to then actually fill that widened cpumask. At that point, the cpumask
scanning will return the NR_CPUS constant, which is _not_ the same as
nr_cpumask_bits.
This just does the mindless fix with
sed -i 's/== nr_cpumask_bits/>= nr_cpu_ids/'
to fix the incorrect uses.
The ones in the SCSI lpfc driver in particular could probably be fixed
more cleanly by just removing that repeated pattern entirely, but I am
not emptionally invested enough in that driver to care.
Reported-and-tested-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/lkml/481b19b5-83a0-4793-b4fd-194ad7b978c3@roeck-us.net/
Reported-and-tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/lkml/CAMuHMdUKo_Sf7TjKzcNDa8Ve+6QrK+P8nSQrSQ=6LTRmcBKNww@mail.gmail.com/
Reported-by: Vernon Yang <vernon2gm@gmail.com>
Link: https://lore.kernel.org/lkml/20230306160651.2016767-1-vernon2gm@gmail.com/
Cc: Yury Norov <yury.norov@gmail.com>
Cc: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The <asm/archrandom.h> header is a random.c private detail, not
something to be called by other code. As such, don't make it
automatically available by way of random.h.
Cc: Michael Ellerman <mpe@ellerman.id.au>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Pull iov_iter updates from Al Viro:
"iov_iter work; most of that is about getting rid of direction
misannotations and (hopefully) preventing more of the same for the
future"
* tag 'pull-iov_iter' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
use less confusing names for iov_iter direction initializers
iov_iter: saner checks for attempt to copy to/from iterator
[xen] fix "direction" argument of iov_iter_kvec()
[vhost] fix 'direction' argument of iov_iter_{init,bvec}()
[target] fix iov_iter_bvec() "direction" argument
[s390] memcpy_real(): WRITE is "data source", not destination...
[s390] zcore: WRITE is "data source", not destination...
[infiniband] READ is "data destination", not source...
[fsi] WRITE is "data source", not destination...
[s390] copy_oldmem_kernel() - WRITE is "data source", not destination
csum_and_copy_to_iter(): handle ITER_DISCARD
get rid of unlikely() on page_copy_sane() calls
The theory behind the jitter dance is that multiple things are poking at
the same cache line. This only works, however, if what's being poked at
is actually all in the same cache line. Ensure this is the case by
aligning the struct on the stack to the cache line size.
We can't use ____cacheline_aligned on a stack variable, because gcc
assumes 16 byte alignment when only 8 byte alignment is provided by the
kernel, which means gcc could technically do something pathological
like `(rsp & ~48) - 64`. It doesn't, but rather than risk it, just do
the stack alignment manually with PTR_ALIGN and an oversized buffer.
Fixes: 50ee7529ec ("random: try to actively add entropy rather than passively wait for it")
Cc: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Rather than just relying on interaction between cache lines of the timer
and the main loop, also explicitly take into account the fact that the
timer might fire at some time that's hard to predict, due to scheduling,
interrupts, or cross-CPU conditions. Mix in a cycle counter during the
firing of the timer, in addition to the existing one during the
scheduling of the timer. It can't hurt and can only help.
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Rather than merely hoping that the callback gets called on another CPU,
arrange for that to actually happen, by round robining which CPU the
timer fires on. This way, on multiprocessor machines, we exacerbate
jitter by touching the same memory from multiple different cores.
There's a little bit of tricky bookkeeping involved here, because using
timer_setup_on_stack() + add_timer_on() + del_timer_sync() will result
in a use after free. See this sample code: <https://xn--4db.cc/xBdEiIKO/c>.
Instead, it's necessary to call [try_to_]del_timer_sync() before calling
add_timer_on(), so that the final call to del_timer_sync() at the end of
the function actually succeeds at making sure no handlers are running.
Cc: Sultan Alsawaf <sultan@kerneltoast.com>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
READ/WRITE proved to be actively confusing - the meanings are
"data destination, as used with read(2)" and "data source, as
used with write(2)", but people keep interpreting those as
"we read data from it" and "we write data to it", i.e. exactly
the wrong way.
Call them ITER_DEST and ITER_SOURCE - at least that is harder
to misinterpret...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This is required by vsprint, because it can't do things synchronously
from hardirq context, and it will be useful for an EFI notifier as well.
I didn't initially want to do this, but with two potential consumers
now, it seems worth it.
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Currently, we reseed when random bytes are requested, if the current
seed is too old. Since random bytes can be requested from all contexts,
including hard IRQ, this means sometimes we wind up adding a bit of
latency to hard IRQ. This was so much of a problem on s390x that now
s390x just doesn't provide its architectural RNG from hard IRQ context,
so we miss out in that case.
Instead, let's just schedule a persistent delayed work, so that the
reseeding and potentially expensive operations will always happen from
process context, reducing unexpected latencies from hard IRQ.
This also has the nice effect of accumulating a transcript of random
inputs over time, since it means that we amass more input values. And it
should make future vDSO integration a bit easier.
Cc: Harald Freudenberger <freude@linux.ibm.com>
Cc: Juergen Christ <jchrist@linux.ibm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Rather than calling add_device_randomness(), the add_early_randomness()
function should use add_hwgenerator_randomness(), so that the early
entropy can be potentially credited, which allows for the RNG to
initialize earlier without having to wait for the kthread to come up.
This requires some minor API refactoring, by adding a `sleep_after`
parameter to add_hwgenerator_randomness(), so that we don't hit a
blocking sleep from add_early_randomness().
Tested-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
The prior text was very old and made outdated references to TCP sequence
numbers, which should use one of the integer functions instead, since
batched entropy was introduced. The current way of describing the
quality of functions is just to say that it's as good as /dev/urandom,
which now all the functions are.
Fixes: f5b98461cb ("random: use chacha20 for get_random_int/long")
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Since de492c83ca ("prandom: remove unused functions"),
get_random_int() no longer exists, so remove its reference from this
comment.
Fixes: de492c83ca ("prandom: remove unused functions")
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
The arch_get_random*_early() abstraction is not completely useful and
adds complexity, because it's not a given that there will be no calls to
arch_get_random*() between random_init_early(), which uses
arch_get_random*_early(), and init_cpu_features(). During that gap,
crng_reseed() might be called, which uses arch_get_random*(), since it's
mostly not init code.
Instead we can test whether we're in the early phase in
arch_get_random*() itself, and in doing so avoid all ambiguity about
where we are. Fortunately, the only architecture that currently
implements arch_get_random*_early() also has an alternatives-based cpu
feature system, one flag of which determines whether the other flags
have been initialized. This makes it possible to do the early check with
zero cost once the system is initialized.
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Jean-Philippe Brucker <jean-philippe@linaro.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
It's very unusual to have both a command line option and a compile time
option, and apparently that's confusing to people. Also, basically
everybody enables the compile time option now, which means people who
want to disable this wind up having to use the command line option to
ensure that anyway. So just reduce the number of moving pieces and nix
the compile time option in favor of the more versatile command line
option.
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Now that we have get_random_u32_below(), it's nearly trivial to make
inline helpers to compute get_random_u32_above() and
get_random_u32_inclusive(), which will help clean up open coded loops
and manual computations throughout the tree.
One snag is that in order to make get_random_u32_inclusive() operate on
closed intervals, we have to do some (unlikely) special case handling if
get_random_u32_inclusive(0, U32_MAX) is called. The least expensive way
of doing this is actually to adjust the slowpath of
get_random_u32_below() to have its undefined 0 result just return the
output of get_random_u32(). We can make this basically free by calling
get_random_u32() before the branch, so that the branch latency gets
interleaved.
Cc: stable@vger.kernel.org # to ease future backports that use this api
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Until the very recent commits, many bounded random integers were
calculated using `get_random_u32() % max_plus_one`, which not only
incurs the price of a division -- indicating performance mostly was not
a real issue -- but also does not result in a uniformly distributed
output if max_plus_one is not a power of two. Recent commits moved to
using `prandom_u32_max(max_plus_one)`, which replaces the division with
a faster multiplication, but still does not solve the issue with
non-uniform output.
For some users, maybe this isn't a problem, and for others, maybe it is,
but for the majority of users, probably the question has never been
posed and analyzed, and nobody thought much about it, probably assuming
random is random is random. In other words, the unthinking expectation
of most users is likely that the resultant numbers are uniform.
So we implement here an efficient way of generating uniform bounded
random integers. Through use of compile-time evaluation, and avoiding
divisions as much as possible, this commit introduces no measurable
overhead. At least for hot-path uses tested, any potential difference
was lost in the noise. On both clang and gcc, code generation is pretty
small.
The new function, get_random_u32_below(), lives in random.h, rather than
prandom.h, and has a "get_random_xxx" function name, because it is
suitable for all uses, including cryptography.
In order to be efficient, we implement a kernel-specific variant of
Daniel Lemire's algorithm from "Fast Random Integer Generation in an
Interval", linked below. The kernel's variant takes advantage of
constant folding to avoid divisions entirely in the vast majority of
cases, works on both 32-bit and 64-bit architectures, and requests a
minimal amount of bytes from the RNG.
Link: https://arxiv.org/pdf/1805.10941.pdf
Cc: stable@vger.kernel.org # to ease future backports that use this api
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
While reworking the archrandom handling, commit d349ab99ee ("random:
handle archrandom with multiple longs") switched to the non-early
archrandom helpers in random_init(), which broke initialization of the
entropy pool from the arm64 random generator.
Indeed at that point the arm64 CPU features, which verify that all CPUs
have compatible capabilities, are not finalized so arch_get_random_seed_longs()
is unsuccessful. Instead random_init() should use the _early functions,
which check only the boot CPU on arm64. On other architectures the
_early functions directly call the normal ones.
Fixes: d349ab99ee ("random: handle archrandom with multiple longs")
Cc: stable@vger.kernel.org
Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
