bpf, arm32: Reject BPF-to-BPF calls and callbacks in the JIT

The ARM32 BPF JIT does not support BPF-to-BPF function calls
(BPF_PSEUDO_CALL) or callbacks (BPF_PSEUDO_FUNC), but it does
not reject them either.

When a program with subprograms is loaded (e.g. libxdp's XDP
dispatcher uses __noinline__ subprograms, or any program using
callbacks like bpf_loop or bpf_for_each_map_elem), the verifier
invokes bpf_jit_subprogs() which calls bpf_int_jit_compile()
for each subprogram.

For BPF_PSEUDO_CALL, since ARM32 does not reject it, the JIT
silently emits code using the wrong address computation:

func = __bpf_call_base + imm

where imm is a pc-relative subprogram offset, producing a bogus
function pointer.

For BPF_PSEUDO_FUNC, the ldimm64 handler ignores src_reg and
loads the immediate as a normal 64-bit value without error.

In both cases, build_body() reports success and a JIT image is
allocated. ARM32 lacks the jit_data/extra_pass mechanism needed
for the second JIT pass in bpf_jit_subprogs(). On the second
pass, bpf_int_jit_compile() performs a full fresh compilation,
allocating a new JIT binary and overwriting prog->bpf_func. The
first allocation is never freed. bpf_jit_subprogs() then detects
the function pointer changed and aborts with -ENOTSUPP, but the
original JIT binary has already been leaked. Each program
load/unload cycle leaks one JIT binary allocation, as reported
by kmemleak:

unreferenced object 0xbf0a1000 (size 4096):
backtrace:
bpf_jit_binary_alloc+0x64/0xfc
bpf_int_jit_compile+0x14c/0x348
bpf_jit_subprogs+0x4fc/0xa60

Fix this by rejecting both BPF_PSEUDO_CALL in the BPF_CALL
handler and BPF_PSEUDO_FUNC in the BPF_LD_IMM64 handler, falling
through to the existing 'notyet' path. This causes build_body()
to fail before any JIT binary is allocated, so
bpf_int_jit_compile() returns the original program unjitted.
bpf_jit_subprogs() then sees !prog->jited and cleanly falls
back to the interpreter with no leak.

Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Fixes: 1c2a088a6626 ("bpf: x64: add JIT support for multi-function programs")
Reported-by: Jonas Rebmann <jre@pengutronix.de>
Closes: https://lore.kernel.org/bpf/b63e9174-7a3d-4e22-8294-16df07a4af89@pengutronix.de
Tested-by: Jonas Rebmann <jre@pengutronix.de>
Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Link: https://lore.kernel.org/r/20260417143353.838911-1-puranjay@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>