kselftest/arm64: build BTI tests in output directory

The arm64 BTI selftests are currently built in the source directory,
then the generated binaries are copied to the output directory.
This leaves the object files around in a potentially otherwise pristine
source tree, tainting it for out-of-tree kernel builds.

Prepend $(OUTPUT) to every reference to an object file in the Makefile,
and remove the extra handling and copying. This puts all generated files
under the output directory.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20230815145931.2522557-1-andre.przywara@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

kselftest/arm64: Explicitly build no BTI tests with BTI disabled

In case a distribution enables branch protection by default do as we do for
the main kernel and explicitly disable branch protection when building the
test case for having BTI disabled to ensure it doesn't get turned on by the
toolchain defaults.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20220516182213.727589-1-broonie@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

kselftest/arm64: bti: force static linking

The "bti" selftests are built with -nostdlib, which apparently
automatically creates a statically linked binary, which is what we want
and need for BTI (to avoid interactions with the dynamic linker).

However this is not true when building a PIE binary, which some
toolchains (Ubuntu) configure as the default.
When compiling btitest with such a toolchain, it will create a
dynamically linked binary, which will probably fail some tests, as the
dynamic linker might not support BTI:
===================
TAP version 13
1..18
not ok 1 nohint_func/call_using_br_x0
not ok 2 nohint_func/call_using_br_x16
not ok 3 nohint_func/call_using_blr
....
===================

To make sure we create static binaries, add an explicit -static on the
linker command line. This forces static linking even if the toolchain
defaults to PIE builds, and fixes btitest runs on BTI enabled machines.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Fixes: 314bcbf09f14 ("kselftest: arm64: Add BTI tests")
Link: https://lore.kernel.org/r/20220511172129.2078337-1-andre.przywara@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

kselftest: arm64: Add BTI tests

Add some tests that verify that BTI functions correctly for static binaries
built with and without BTI support, verifying that SIGILL is generated when
expected and is not generated in other situations.

Since BTI support is still being rolled out in distributions these tests
are built entirely free standing, no libc support is used at all so none
of the standard helper functions for kselftest can be used and we open
code everything. This also means we aren't testing the kernel support for
the dynamic linker, though the test program can be readily adapted for
that once it becomes something that we can reliably build and run.

These tests were originally written by Dave Martin, I've adapted them for
kselftest, mainly around the build system and the output format.

Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: Dave Martin <Dave.Martin@arm.com>
Link: https://lore.kernel.org/r/20210309193731.57247-1-broonie@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>