wireguard: selftests: set fake real time in init

Not all platforms have an RTC, and rather than trying to force one into
each, it's much easier to just set a fixed time. This is necessary
because WireGuard's latest handshakes parameter is returned in wallclock
time, and if the system time isn't set, and the system is really fast,
then this returns 0, which trips the test.

Turning this on requires setting CONFIG_COMPAT_32BIT_TIME=y, as musl
doesn't support settimeofday without it.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

wireguard: selftests: set panic_on_warn=1 from cmdline

Rather than setting this once init is running, set panic_on_warn from
the kernel command line, so that it catches splats from WireGuard
initialization code and the various crypto selftests.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

wireguard: selftests: import harness makefile for test suite

WireGuard has been using this on build.wireguard.com for the last
several years with considerable success. It allows for very quick and
iterative development cycles, and supports several platforms.

To run the test suite on your current platform in QEMU:

$ make -C tools/testing/selftests/wireguard/qemu -j$(nproc)

To run it with KASAN and such turned on:

$ DEBUG_KERNEL=yes make -C tools/testing/selftests/wireguard/qemu -j$(nproc)

To run it emulated for another platform in QEMU:

$ ARCH=arm make -C tools/testing/selftests/wireguard/qemu -j$(nproc)

At the moment, we support aarch64_be, aarch64, arm, armeb, i686, m68k,
mips64, mips64el, mips, mipsel, powerpc64le, powerpc, and x86_64.

The system supports incremental rebuilding, so it should be very fast to
change a single file and then test it out and have immediate feedback.

This requires for the right toolchain and qemu to be installed prior.
I've had success with those from musl.cc.

This is tailored for WireGuard at the moment, though later projects
might generalize it for other network testing.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: David S. Miller <davem@davemloft.net>