[Qemu-devel] [PATCH for-4.1 0/7] Add qemu_getrandom and ARMv8.5-RNG

[Richard Henderson]

While the comment for AT_RANDOM is still apropos, "not cryptically
secure but it's not the aim of QEMU", I think we can still do better
than N calls to rand(3).

The first patch sets up an interface that allows deterministic random
numbers across different threads, using jrand48.  This function is:
(1) in POSIX, so is easy to assume,
(2) produces full 32-bit random numbers, as opposed to RAND_MAX,
    making it easier to fill N bytes,
(3) has a much larger periodicity,
(4) is thread-safe (with restricted usage).

The second patch allows the use of getrandom(2), if available.
But if the -seed command-line option is used, we continue to
use the deterministic algorithm.

I leave the task of adding support for Windows BCryptGenRandom,
and BSD getentropy, to someone else.  I didn't think it was worth it
to do anything with /dev/urandom, in case getrandom isn't present.

I replaced the existing major users of rand(3).  There are a few left,
mostly within hw/.  I'm really not sure whether it's worth changing
those, or what to do about them.

This could quickly be used to implement Power9's helper_darn{32,64},
or for implementing RDRAND for x86_64.  I'm less sure about S390's
PRNO instruction; that seems to expose a lot of the DRNG at an
architectural level.


r~


Richard Henderson (7):
  util: Add qemu_getrandom and support functions
  util: Use getrandom for qemu_getrandom if available
  linux-user: Use qemu_getrandom for AT_RANDOM
  linux-user/aarch64: Use qemu_getrandom for arm_init_pauth_key
  linux-user: Remove srand call
  ui/vnc: Use qemu_getrandom for make_challenge
  target/arm: Implement ARMv8.5-RNG

 include/qemu/random.h         |  58 ++++++++++++++
 include/qom/cpu.h             |   1 +
 target/arm/cpu.h              |   5 ++
 cpus.c                        |   9 +++
 linux-user/aarch64/cpu_loop.c |  16 +---
 linux-user/elfload.c          |   8 +-
 linux-user/main.c             |  11 +--
 linux-user/syscall.c          |   3 +
 target/arm/cpu64.c            |   1 +
 target/arm/helper.c           |  32 ++++++++
 ui/vnc.c                      |   8 +-
 util/random.c                 | 140 ++++++++++++++++++++++++++++++++++
 vl.c                          |   4 +
 configure                     |  18 ++++-
 qemu-options.hx               |  10 +++
 util/Makefile.objs            |   1 +
 16 files changed, 290 insertions(+), 35 deletions(-)
 create mode 100644 include/qemu/random.h
 create mode 100644 util/random.c

-- 
2.17.1