From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from 66-220-144-179.mail-mxout.facebook.com (66-220-144-179.mail-mxout.facebook.com [66.220.144.179]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id F14BD280331 for ; Wed, 19 Aug 2026 05:53:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=66.220.144.179 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787118808; cv=none; b=KtsKYTHj8PcuspBnDBfCV7ZTPbUf9XaFuf7FtvRnzSlu3156eEnCGclbKhjL9wodrVNub0ZOVJMZ5SIdImzbUFkyj/++0VNXK3QR724I6Cc6cdyQEVphs7upS6BKbCjQ8ShYLQQmVsjG538Hz+RlttTU5GT3tVDYO0wyq/Y7k8U= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787118808; c=relaxed/simple; bh=vArhAC7oMq+u5xO3HMOU7SzHMv1VTNB5VIcfApnBvPE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=FkpP+y3++WtBS1xHGXeZtvGfGnGgy4yoymuf8vMH1JlxJklm79t1zbUynkjbo5nep6nDYb/Qo4TWZQV9deOLclGfKVszW5q+YkRVfFhuH9XLKnpSyApWkZ4ZifFfUkuKB+S1rvdR6W9cEBZcLh0sFrmAl/MluX5o8cmev2bGplE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.dev; spf=fail smtp.mailfrom=linux.dev; arc=none smtp.client-ip=66.220.144.179 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=linux.dev Received: by devvm16039.vll0.facebook.com (Postfix, from userid 128203) id E34FF250AA3997; Tue, 18 Aug 2026 22:53:14 -0700 (PDT) From: Yonghong Song To: bpf@vger.kernel.org Cc: Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Eduard Zingerman , kernel-team@fb.com Subject: [PATCH bpf-next v7 07/10] bpf: Enable aggregate return types up to 16 bytes Date: Tue, 18 Aug 2026 22:53:14 -0700 Message-ID: <20260819055314.3298664-1-yonghong.song@linux.dev> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260819055239.3293449-1-yonghong.song@linux.dev> References: <20260819055239.3293449-1-yonghong.song@linux.dev> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Relax btf_distill_func_proto() to accept a by-value struct or union that the R0:R2 convention added in earlier patches can carry: - a struct or union larger than 8 and up to 16 bytes, returned in the R0:R2 register pair, matching what LLVM emits for the BPF target; - a struct or union up to 8 bytes, returned in R0 alone. A >8 byte scalar (__int128) was already accepted and is unchanged. Everything else stays rejected: a return type larger than 16 bytes, and a= ny type that __get_type_size() cannot return in registers at all (e.g. an array), which it already reports as ret < 0. btf_validate_return_type() is relaxed as well, so that it accepts a by-value struct or union up to 16 bytes in addition to void and scalars. With btf_distill_func_proto() and btf_validate_return_type() relaxed, the verifier, JIT, precision-backtracking and live-register support from the earlier patches becomes reachable: <=3D16 byte aggregate return values no= w work end to end. Acked-by: Eduard Zingerman Signed-off-by: Yonghong Song --- include/linux/bpf_verifier.h | 2 ++ kernel/bpf/btf.c | 23 +++++++++++++++---- kernel/bpf/verifier.c | 18 +++++++-------- .../selftests/bpf/progs/exceptions_fail.c | 2 +- 4 files changed, 30 insertions(+), 15 deletions(-) diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h index 953d8191563a..004b06785521 100644 --- a/include/linux/bpf_verifier.h +++ b/include/linux/bpf_verifier.h @@ -1488,6 +1488,8 @@ int bpf_jmp_offset(struct bpf_insn *insn); struct bpf_iarray *bpf_insn_successors(struct bpf_verifier_env *env, u32= idx); void bpf_fmt_stack_mask(char *buf, ssize_t buf_sz, u64 stack_mask); bool bpf_subprog_is_global(const struct bpf_verifier_env *env, int subpr= og); +bool btf_type_is_scalar_struct(struct bpf_verifier_env *env, const struc= t btf *btf, + const struct btf_type *t, int rec); =20 int bpf_find_subprog(struct bpf_verifier_env *env, int off); bool bpf_is_throw_kfunc(struct bpf_insn *insn); diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index 5e9f6a487524..58b81c6f5288 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -7591,7 +7591,7 @@ int btf_distill_func_proto(struct bpf_verifier_log = *log, return -EINVAL; } ret =3D __get_type_size(btf, func->type, &t); - if (ret < 0 || btf_type_is_struct(t)) { + if (ret < 0 || ret > 16) { bpf_log(log, "The function %s return type %s is unsupported.\n", tname, btf_type_str(t)); @@ -7970,7 +7970,7 @@ static int btf_scan_type_tags(struct bpf_verifier_e= nv *env, =20 /* Check whether the type is a valid return type. */ static int btf_validate_return_type(struct bpf_verifier_env *env, struct= btf *btf, - const struct btf_type *t, int subprog) + const struct btf_type *t, int subprog, bool is_global) { u32 tags =3D 0; int err; @@ -7993,6 +7993,19 @@ static int btf_validate_return_type(struct bpf_ver= ifier_env *env, struct btf *bt if (btf_type_is_void(t) || btf_type_is_int(t) || btf_is_any_enum(t)) return 0; =20 + if (btf_type_is_struct(t) && t->size <=3D 16) { + /* + * A global function's caller models the return as an opaque + * scalar pair, so it may only return scalars by value. A local + * function is verified inline, so a pointer field stays tracked + * and needs no such restriction. + */ + bool local_func =3D subprog && !is_global; + + if (local_func || btf_type_is_scalar_struct(env, btf, t, 0)) + return 0; + } + return -EOPNOTSUPP; } =20 @@ -8080,12 +8093,12 @@ int btf_prepare_func_args(struct bpf_verifier_env= *env, int subprog) return -EINVAL; } =20 - err =3D btf_validate_return_type(env, btf, t, subprog); + err =3D btf_validate_return_type(env, btf, t, subprog, is_global); if (err) { if (is_global) { bpf_log(log, - "Global function %s() return value not void or scalar. " - "Only those are supported.\n", + "Global function %s() has unsupported return type. " + "Only void, scalar, or a scalar-only struct/union up to 16 bytes is = supported.\n", tname); } return err; diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index d79f0c069795..7a939dfa3797 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -11594,9 +11594,9 @@ static bool is_kfunc_arg_implicit(const struct bp= f_call_arg_meta *meta, u32 arg_ } =20 /* Returns true if struct is composed of scalars, 4 levels of nesting al= lowed */ -static bool __btf_type_is_scalar_struct(struct bpf_verifier_env *env, - const struct btf *btf, - const struct btf_type *t, int rec) +bool btf_type_is_scalar_struct(struct bpf_verifier_env *env, + const struct btf *btf, + const struct btf_type *t, int rec) { const struct btf_type *member_type; const struct btf_member *member; @@ -11614,7 +11614,7 @@ static bool __btf_type_is_scalar_struct(struct bp= f_verifier_env *env, verbose(env, "max struct nesting depth exceeded\n"); return false; } - if (!__btf_type_is_scalar_struct(env, btf, member_type, rec + 1)) + if (!btf_type_is_scalar_struct(env, btf, member_type, rec + 1)) return false; continue; } @@ -12013,7 +12013,7 @@ get_kfunc_arg_type(struct bpf_verifier_env *env, = struct bpf_call_arg_meta *meta, (is_kfunc_arg_mem_size(meta->btf, &args[arg + 1]) || is_kfunc_arg_const_mem_size(meta->btf, &args[arg + 1]))) { if (!btf_type_is_void(ref_t) && !btf_type_is_scalar(ref_t) && - !__btf_type_is_scalar_struct(env, meta->btf, ref_t, 0)) { + !btf_type_is_scalar_struct(env, meta->btf, ref_t, 0)) { verbose(env, "%s pointer type %s %s must point to void, scalar, or st= ruct with scalar\n", reg_arg_name(env, argno), btf_type_str(ref_t), ref_tname); return -EINVAL; @@ -12029,7 +12029,7 @@ get_kfunc_arg_type(struct bpf_verifier_env *env, = struct bpf_call_arg_meta *meta, * scalars. The access size is derived from the pointed-to BTF type. */ if (!btf_type_is_scalar(ref_t) && - !__btf_type_is_scalar_struct(env, meta->btf, ref_t, 0)) { + !btf_type_is_scalar_struct(env, meta->btf, ref_t, 0)) { verbose(env, "%s pointer type %s %s must point to scalar, or struct w= ith scalar\n", reg_arg_name(env, argno), btf_type_str(ref_t), ref_tname); return -EINVAL; @@ -13085,7 +13085,7 @@ static int check_kfunc_args(struct bpf_verifier_e= nv *env, struct bpf_call_arg_me break; } =20 - if (!__btf_type_is_scalar_struct(env, meta->btf, ref_t, 0)) { + if (!btf_type_is_scalar_struct(env, meta->btf, ref_t, 0)) { enum bpf_reg_type reg2btf_type =3D lookup_reg2btf_ids(ref_id); const char *expected_type; =20 @@ -13627,7 +13627,7 @@ static int check_special_kfunc(struct bpf_verifie= r_env *env, struct bpf_call_arg =20 struct_meta =3D btf_find_struct_meta(ret_btf, ret_btf_id); if (is_bpf_percpu_obj_new_kfunc(meta->func_id)) { - if (!__btf_type_is_scalar_struct(env, ret_btf, ret_t, 0)) { + if (!btf_type_is_scalar_struct(env, ret_btf, ret_t, 0)) { verbose(env, "bpf_percpu_obj_new type ID argument must be of a struc= t of scalars\n"); return -EINVAL; } @@ -14006,7 +14006,7 @@ static int check_kfunc_call(struct bpf_verifier_e= nv *env, struct bpf_insn *insn, * otherwise a pointer field would be laundered into a scalar * and escape provenance and reference tracking. */ - if (!__btf_type_is_scalar_struct(env, desc_btf, t, 0)) { + if (!btf_type_is_scalar_struct(env, desc_btf, t, 0)) { verbose(env, "kernel function %s returns %s %s that is not composed of scalars\n"= , func_name, btf_type_str(t), diff --git a/tools/testing/selftests/bpf/progs/exceptions_fail.c b/tools/= testing/selftests/bpf/progs/exceptions_fail.c index ac44d60e5066..9708efb93683 100644 --- a/tools/testing/selftests/bpf/progs/exceptions_fail.c +++ b/tools/testing/selftests/bpf/progs/exceptions_fail.c @@ -60,7 +60,7 @@ __noinline int exception_cb_ok_arg_small(int a) =20 SEC("?tc") __exception_cb(exception_cb_bad_ret_type1) -__failure __msg("Global function exception_cb_bad_ret_type1() return val= ue not void or scalar.") +__failure __msg("Only void, scalar, or a scalar-only struct/union up to = 16 bytes is supported.") int reject_exception_cb_type_1(struct __sk_buff *ctx) { bpf_throw(0); --=20 2.53.0-Meta