selftests/bpf: Move kfunc exports to bpf_testmod/bpf_testmod_kfunc.h

Move all kfunc exports into separate bpf_testmod_kfunc.h header file
and include it in tests that need it.

We will move all test kfuncs into bpf_testmod in following change,
so it's convenient to have declarations in single place.

The bpf_testmod_kfunc.h is included by both bpf_testmod and bpf
programs that use test kfuncs.

As suggested by David, the bpf_testmod_kfunc.h includes vmlinux.h
and bpf/bpf_helpers.h for bpf programs build, so the declarations
have proper __ksym attribute and we can resolve all the structs.

Note in kfunc_call_test_subprog.c we can no longer use the sk_state
define from bpf_tcp_helpers.h (because it clashed with vmlinux.h)
and we need to address __sk_common.skc_state field directly.

Acked-by: David Vernet <void@manifault.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20230515133756.1658301-3-jolsa@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

bpf: Rename __kptr_ref -> __kptr and __kptr -> __kptr_untrusted.

__kptr meant to store PTR_UNTRUSTED kernel pointers inside bpf maps.
The concept felt useful, but didn't get much traction,
since bpf_rdonly_cast() was added soon after and bpf programs received
a simpler way to access PTR_UNTRUSTED kernel pointers
without going through restrictive __kptr usage.

Rename __kptr_ref -> __kptr and __kptr -> __kptr_untrusted to indicate
its intended usage.
The main goal of __kptr_untrusted was to read/write such pointers
directly while bpf_kptr_xchg was a mechanism to access refcnted
kernel pointers. The next patch will allow RCU protected __kptr access
with direct read. At that point __kptr_untrusted will be deprecated.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: David Vernet <void@manifault.com>
Link: https://lore.kernel.org/bpf/20230303041446.3630-2-alexei.starovoitov@gmail.com

selftests/bpf: Add verifier test exercising jit PROBE_MEM logic

This patch adds a test exercising logic that was fixed / improved in
the previous patch in the series, as well as general sanity checking for
jit's PROBE_MEM logic which should've been unaffected by the previous
patch.

The added verifier test does the following:

* Acquire a referenced kptr to struct prog_test_ref_kfunc using
existing net/bpf/test_run.c kfunc
* Helper returns ptr to a specific prog_test_ref_kfunc whose first
two fields - both ints - have been prepopulated w/ vals 42 and
108, respectively
* kptr_xchg the acquired ptr into an arraymap
* Do a direct map_value load of the just-added ptr
* Goal of all this setup is to get an unreferenced kptr pointing to
struct with ints of known value, which is the result of this step
* Using unreferenced kptr obtained in previous step, do loads of
prog_test_ref_kfunc.a (offset 0) and .b (offset 4)
* Then incr the kptr by 8 and load prog_test_ref_kfunc.a again (this
time at offset -8)
* Add all the loaded ints together and return

Before the PROBE_MEM fixes in previous patch, the loads at offset 0 and
4 would succeed, while the load at offset -8 would incorrectly fail
runtime check emitted by the JIT and 0 out dst reg as a result. This
confirmed by retval of 150 for this test before previous patch - since
second .a read is 0'd out - and a retval of 192 with the fixed logic.

The test exercises the two optimizations to fixed logic added in last
patch as well:

* First load, with insn "r8 = *(u32 *)(r9 + 0)" exercises "insn->off
is 0, no need to add / sub from src_reg" optimization
* Third load, with insn "r9 = *(u32 *)(r9 - 8)" exercises "src_reg ==
dst_reg, no need to restore src_reg after load" optimization

Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20221216214319.3408356-2-davemarchevsky@fb.com