bpf: don't infer PTR_TO_CTX for programs with unnamed context type

For program types that don't have named context type name (e.g., BPF
iterator programs or tracepoint programs), ctx_tname will be a non-NULL
empty string. For such programs it shouldn't be possible to have
PTR_TO_CTX argument for global subprogs based on type name alone.
arg:ctx tag is the only way to have PTR_TO_CTX passed into global
subprog for such program types.

Fix this loophole, which currently would assume PTR_TO_CTX whenever
user uses a pointer to anonymous struct as an argument to their global
subprogs. This happens in practice with the following (quite common, in
practice) approach:

typedef struct { /* anonymous */
int x;
} my_type_t;

int my_subprog(my_type_t *arg) { ... }

User's intent is to have PTR_TO_MEM argument for `arg`, but verifier
will complain about expecting PTR_TO_CTX.

This fix also closes unintended s390x-specific KPROBE handling of
PTR_TO_CTX case. Selftest change is necessary to accommodate this.

Fixes: 91cc1a99740e ("bpf: Annotate context types")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20240212233221.2575350-4-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

selftests/bpf: add arg:ctx cases to test_global_funcs tests

Add a few extra cases of global funcs with context arguments. This time
rely on "arg:ctx" decl_tag (__arg_ctx macro), but put it next to
"classic" cases where context argument has to be of an exact type that
BPF verifier expects (e.g., bpf_user_pt_regs_t for kprobe/uprobe).

Colocating all these cases separately from other global func args that
rely on arg:xxx decl tags (in verifier_global_subprogs.c) allows for
simpler backwards compatibility testing on old kernels. All the cases in
test_global_func_ctx_args.c are supposed to work on older kernels, which
was manually validated during development.

Acked-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20240104013847.3875810-9-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

selftests/bpf: Add global subprog context passing tests

Add tests validating that it's possible to pass context arguments into
global subprogs for various types of programs, including a particularly
tricky KPROBE programs (which cover kprobes, uprobes, USDTs, a vast and
important class of programs).

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/bpf/20230216045954.3002473-4-andrii@kernel.org