github-mirror/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-06-08 14:42:37 +02:00
Code Issues Actions Packages Projects Releases Wiki Activity Graph
Linux kernel source tree
796,584 Commits 1 Branch 934 Tags 20 GiB
C 97%
Assembly 1%
Shell 0.6%
Rust 0.5%
Python 0.4%
Other 0.3%
259f9d9a29
Go to file
Jason A. Donenfeld 259f9d9a29 random: always use batched entropy for get_random_u{32,64} 
commit 69efea712f upstream.

It turns out that RDRAND is pretty slow. Comparing these two
constructions:

  for (i = 0; i < CHACHA_BLOCK_SIZE; i += sizeof(ret))
    arch_get_random_long(&ret);

and

  long buf[CHACHA_BLOCK_SIZE / sizeof(long)];
  extract_crng((u8 *)buf);

it amortizes out to 352 cycles per long for the top one and 107 cycles
per long for the bottom one, on Coffee Lake Refresh, Intel Core i9-9880H.

And importantly, the top one has the drawback of not benefiting from the
real rng, whereas the bottom one has all the nice benefits of using our
own chacha rng. As get_random_u{32,64} gets used in more places (perhaps
beyond what it was originally intended for when it was introduced as
get_random_{int,long} back in the md5 monstrosity era), it seems like it
might be a good thing to strengthen its posture a tiny bit. Doing this
should only be stronger and not any weaker because that pool is already
initialized with a bunch of rdrand data (when available). This way, we
get the benefits of the hardware rng as well as our own rng.

Another benefit of this is that we no longer hit pitfalls of the recent
stream of AMD bugs in RDRAND. One often used code pattern for various
things is:

  do {
  	val = get_random_u32();
  } while (hash_table_contains_key(val));

That recent AMD bug rendered that pattern useless, whereas we're really
very certain that chacha20 output will give pretty distributed numbers,
no matter what.

So, this simplification seems better both from a security perspective
and from a performance perspective.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20200221201037.30231-1-Jason@zx2c4.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-04-13 10:45:09 +02:00
arch arm64: dts: ls1046ardb: set RGMII interfaces to RGMII_ID mode 2020-04-02 15:28:25 +02:00
block block, bfq: fix overwrite of bfq_group pointer in bfq_find_set_group() 2020-03-25 08:06:08 +01:00
certs export.h: remove VMLINUX_SYMBOL() and VMLINUX_SYMBOL_STR() 2018-08-22 23:21:44 +09:00
crypto crypto: api - Fix race condition in crypto_spawn_alg 2020-02-11 04:34:05 -08:00
Documentation dt-bindings: net: FMan erratum A050385 2020-04-02 15:28:14 +02:00
drivers random: always use batched entropy for get_random_u{32,64} 2020-04-13 10:45:09 +02:00
firmware Fix built-in early-load Intel microcode alignment 2020-01-23 08:21:29 +01:00
fs libfs: fix infoleak in simple_attr_read() 2020-04-02 15:28:21 +02:00
include include/linux/notifier.h: SRCU: fix ctags 2020-04-13 10:45:06 +02:00
init fork: fix some -Wmissing-prototypes warnings 2019-12-05 09:21:04 +01:00
ipc Revert "ipc,sem: remove uneeded sem_undo_list lock usage in exit_sem()" 2020-02-28 16:38:49 +01:00
kernel padata: always acquire cpu_hotplug_lock before pinst->lock 2020-04-13 10:45:05 +02:00
lib lib/stackdepot.c: fix global out-of-bounds in stack_slabs 2020-02-28 16:38:55 +01:00
LICENSES LICENSES: Remove CC-BY-SA-4.0 license text 2018-10-18 11:28:50 +02:00
mm mm: mempolicy: require at least one nodeid for MPOL_PREFERRED 2020-04-13 10:45:06 +02:00
net ipv6: don't auto-add link-local address to lag ports 2020-04-13 10:45:07 +02:00
samples samples/bpf: Don't try to remove user's homedir on clean 2020-02-11 04:34:05 -08:00
scripts scripts/dtc: Remove redundant YYLOC global declaration 2020-04-02 15:28:17 +02:00
security selinux: ensure we cleanup the internal AVC counters on error in avc_update() 2020-02-24 08:34:43 +01:00
sound ALSA: hda/ca0132 - Add Recon3Di quirk to handle integrated sound on EVGA X99 Classified motherboard 2020-04-13 10:45:04 +02:00
tools tools/power turbostat: Fix missing SYS_LPI counter on some Chromebooks 2020-04-13 10:45:01 +02:00
usr initramfs: restore default compression behavior 2020-04-13 10:44:59 +02:00
virt KVM: Check for a bad hva before dropping into the ghc slow path 2020-03-05 16:42:21 +01:00
.clang-format clang-format: Set IndentWrappedFunctionNames false 2018-08-01 18:38:51 +02:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Kbuild updates for v4.17 (2nd) 2018-04-15 17:21:30 -07:00
.mailmap libnvdimm-for-4.19_misc 2018-08-25 18:13:10 -07:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS 9p: remove Ron Minnich from MAINTAINERS 2018-08-17 16:20:26 -07:00
Kbuild Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
Kconfig kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt 2018-08-02 08:06:55 +09:00
MAINTAINERS MAINTAINERS: Update drm/i915 bug filing URL 2020-02-28 16:38:49 +01:00
Makefile Linux 4.19.114 2020-04-02 15:28:25 +02:00
README Docs: Added a pointer to the formatted docs to README 2018-03-21 09:02:53 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.