From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from 66-220-144-178.mail-mxout.facebook.com (66-220-144-178.mail-mxout.facebook.com [66.220.144.178]) (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 335DE3D5221 for ; Wed, 8 Jul 2026 20:10:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=66.220.144.178 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783541436; cv=none; b=E83DJYL9vEg990HZWpozGSnJDzo4pUKjsdOtWfz5aAYU1G9JpthzGEek+U7fkKZGkC9dxg6aM2ZQxYxNWQMRsEUXeLDSC/NRotyoWlSaawyfIJpgSoKHGHSgiwj+JLuZyv3ybYZxKdYji74MA5r0aUCPwy14j29Njh4x+zgV7xM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783541436; c=relaxed/simple; bh=uZ5w4PbhT6cC3ub5i4FzF5uqz/znJBx5tZn1P8ebwfk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=ENDL0hcAblxECVYmT4CnGMR/uv98T0lstvgAaWNPID5RTilqH9chcYTrLGBuWeup0NmELsgp7pPJUvY9gy9+q1l6F1rQhQDzYbAb9R4jhU8rZWX/VGHVI/iaSl5Cla/DEl/btTaR6jc+7v9D66Uk5Z/bXSjfNiUInQy7/AC62pY= 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=66.220.144.178 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 B84D21D0B6F935; Wed, 8 Jul 2026 13:10:20 -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 08/12] bpf: Enable 16-byte aggregate return types Date: Wed, 8 Jul 2026 13:10:20 -0700 Message-ID: <20260708201020.2160131-1-yonghong.song@linux.dev> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260708200939.2153664-1-yonghong.song@linux.dev> References: <20260708200939.2153664-1-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_distill_func_proto() also builds the trampoline (fentry/fexit/fmod_re= t) and struct_ops function models. Allowing up to 16 bytes here is safe: the previous patch already rejects >8 byte returns on the return-reading path= s, where the trampoline preserves only 8 bytes of the return value. btf_validate_return_type() is relaxed as 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, live-register and trampoline-guard preparation from the earlier patches becomes reachable: this final patch enables <=3D16 byte aggregate return values end to end. Signed-off-by: Yonghong Song --- include/linux/bpf_verifier.h | 2 ++ kernel/bpf/btf.c | 14 +++++++++++--- kernel/bpf/verifier.c | 6 +++--- .../testing/selftests/bpf/progs/exceptions_fail.c | 2 +- 4 files changed, 17 insertions(+), 7 deletions(-) diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h index fa255f326240..ae4dae8e57f9 100644 --- a/include/linux/bpf_verifier.h +++ b/include/linux/bpf_verifier.h @@ -1433,6 +1433,8 @@ 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 bpf_ret_reg_pair(struct bpf_verifier_env *env, int subprog); int bpf_get_kfunc_ret_size(const struct bpf_prog *prog, u32 func_id, u16= offset); +bool __btf_type_is_scalar_struct(struct bpf_verifier_env *env, const str= uct 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 dff5c0d91641..bab82d1c8cb9 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -7572,7 +7572,12 @@ 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)) { + /* + * __get_type_size() already restricts a non-negative ret to void, a + * pointer, an int, an enum or a struct/union, so only the size is chec= ked + * here. + */ + if (ret < 0 || ret > 16) { bpf_log(log, "The function %s return type %s is unsupported.\n", tname, btf_type_str(t)); @@ -7968,6 +7973,9 @@ static int btf_validate_return_type(struct bpf_veri= fier_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 && __btf_type_is_scalar_st= ruct(env, btf, t, 0)) + return 0; + return -EOPNOTSUPP; } =20 @@ -8059,8 +8067,8 @@ int btf_prepare_func_args(struct bpf_verifier_env *= env, int subprog) 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 121f56e3fb16..bf451a2d7095 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -11082,9 +11082,9 @@ static bool is_kfunc_arg_implicit(const struct bp= f_kfunc_call_arg_meta *meta, u3 } =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; 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