bpf: Rewrite any fault prone load out of a mem or btf_id pointer

bpf_convert_ctx_accesses() turns a BPF_LDX into a BPF_PROBE_MEM one by
matching the type recorded for the insn against a list of exact pointer
types. The list cannot keep up with the flag combinations the verifier
produces, and a type which is missing from it ends up as a plain load
without an exception table entry, so a bad address panics the kernel
instead of being handled.

Two such types exist today and are reachable:

  - PTR_TO_BTF_ID | PTR_UNTRUSTED | MEM_ALLOC | NON_OWN_REF
  - PTR_TO_BTF_ID | PTR_UNTRUSTED | MEM_RCU

Rather than adding the two, just drop the list and state the property
itself in the default case of the switch. This is a superset of what
the list matched, the untrusted PTR_TO_MEM does not have to carry
MEM_RDONLY for it anymore, and it stays in sync with the verifier side
which uses the same match in save_aux_ptr_type() and reg_type_mismatch_ok().

Assert that a fault prone type which does not get the rewrite for whatever
reason is rejected at load time rather than left to fault at runtime to
catch any future cases.

Fixes: 1b12171533a9 ("bpf: Mark direct ld of stashed bpf_{rb,list}_node as non-owning ref")
Fixes: 6fcd486b3a0a ("bpf: Refactor RCU enforcement in the verifier.")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/bpf/20260814215301.709827-4-daniel@iogearbox.net

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