bpf: support for void/primitive __arg_untrusted global func params

Allow specifying __arg_untrusted for void */char */int */long *
parameters. Treat such parameters as
PTR_TO_MEM|MEM_RDONLY|PTR_UNTRUSTED of size zero.
Intended usage is as follows:

  int memcmp(char *a __arg_untrusted, char *b __arg_untrusted, size_t n) {
    bpf_for(i, 0, n) {
      if (a[i] - b[i])      // load at any offset is allowed
        return a[i] - b[i];
    }
    return 0;
  }

Allocate register id for ARG_PTR_TO_MEM parameters only when
PTR_MAYBE_NULL is set. Register id for PTR_TO_MEM is used only to
propagate non-null status after conditionals.

Suggested-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20250704230354.1323244-8-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/btf.h b/include/linux/btf.h
index a40beb9cf160..9eda6b113f9b 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -223,6 +223,7 @@ u32 btf_nr_types(const struct btf *btf);
 struct btf *btf_base_btf(const struct btf *btf);
 bool btf_type_is_i32(const struct btf_type *t);
 bool btf_type_is_i64(const struct btf_type *t);
+bool btf_type_is_primitive(const struct btf_type *t);
 bool btf_member_is_reg_int(const struct btf *btf, const struct btf_type *s,
 			   const struct btf_member *m,
 			   u32 expected_offset, u32 expected_size);