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 66D3237C93E for ; Sat, 29 Aug 2026 06:15:57 +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=1787984158; cv=none; b=YZ7CCyZzixe/GhBFt2NJsasAu6sWBYnF5Dt88a+rlkwFQKpRkLS7GELSU84X1AcLTPdlws3P9Z5RrSWGwVGROfXAp13O8KnG4d9bSvAGtJCPaKIzXT2mJhCRxea1vPLmOiZVIHh1vWL32OVVLW/lv5Ds/ety+S8Z8zOfci516eQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787984158; c=relaxed/simple; bh=1S4k0VBIBICBA13ml6xocN2HnmL8YtpsghUWc3r9vE4=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=TPfK5vSgYTuvyZml49BwqrEbdRZCrZTPBxPQIbN04psWoiEE7HmHYJP9iUpbmHnv00uAyB0ZQ83Zc2esrhxVOiD6NlMxRwvnzVer5R079AS5x915IxeMXUQeb5dArxjBCryy3uE5CxbRZPCeqr7Buxfn6Z14fddARulBGAsr2Zc= 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 3B9D7273BA2FDD; Fri, 28 Aug 2026 23:15:55 -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 v4 08/12] bpf: Allow arena pointers in a by-value kfunc return Date: Fri, 28 Aug 2026 23:15:55 -0700 Message-ID: <20260829061555.1697503-1-yonghong.song@linux.dev> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260829061514.1690730-1-yonghong.song@linux.dev> References: <20260829061514.1690730-1-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 A kfunc may already return an arena pointer on its own, which the program casts back into the arena address space to use. Let the members of a by-value struct it returns be arena pointers as well, rather than scalars only. Such a member carries the arena type tag but not the address space qualifier, so the program has to cast it itself. Handing it back as a scalar costs nothing: an arena address has no provenance to track, and th= e cast is confined to the caller's arena. Signed-off-by: Yonghong Song --- kernel/bpf/verifier.c | 22 +++++++++++-------- .../selftests/bpf/progs/aggregate_ret_kfunc.c | 2 +- 2 files changed, 14 insertions(+), 10 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 745daf58b052..a725e3917976 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -14138,13 +14138,16 @@ static int check_kfunc_call(struct bpf_verifier= _env *env, struct bpf_insn *insn, =20 /* * The returned struct comes back as raw register bits modeled - * as an unknown scalar, so it must contain only scalars: - * otherwise a pointer field would be laundered into a scalar - * and escape provenance and reference tracking. + * as an unknown scalar, so a pointer member would be laundered + * into a scalar and escape provenance and reference tracking. + * Only scalars and arena pointers are allowed; see + * btf_validate_return_type() in btf.c for why an arena pointer + * is safe here. */ - if (!btf_struct_member_walk(env, desc_btf, t, BTF_MEMBER_SCALAR, 0, &p= ath)) { + if (!btf_struct_member_walk(env, desc_btf, t, + BTF_MEMBER_SCALAR | BTF_MEMBER_ARENA_PTR, 0, &path)) { verbose(env, - "kernel function %s returns %s %s that is not composed of scalars\n"= , + "kernel function %s returns %s %s that is not composed of scalars or= arena pointers\n", func_name, btf_type_str(t), btf_name_by_offset(desc_btf, t->name_off)); if (path.too_deep) { @@ -14165,16 +14168,17 @@ static int check_kfunc_call(struct bpf_verifier= _env *env, struct bpf_insn *insn, verbose(env, "member '%s' has type %s\n", bad_name, btf_type_str(path.bad_type)); member_note =3D bpf_diag_fmt( - env, " Its member '%s' is %s, not a scalar.", + env, + " Its member '%s' is %s, not a scalar or an arena pointer.", bad_name, btf_type_str(path.bad_type)); } } bpf_diag_program_structure( env, insn_idx, "unsupported kernel function return type", - "Call a kernel function that returns only scalars by value.", + "Call a kernel function that returns only scalars or arena pointers = by value.", "%s() returns %s %s by value.%s " - "Only kfuncs returning scalar values, or " - "structures composed of scalar values are " + "Only kfuncs returning scalar values or arena pointers, or " + "structures composed of scalar values or arena pointers are " "supported.", func_name, btf_type_str(t), btf_name_by_offset(desc_btf, t->name_off), member_note); diff --git a/tools/testing/selftests/bpf/progs/aggregate_ret_kfunc.c b/to= ols/testing/selftests/bpf/progs/aggregate_ret_kfunc.c index d6b422ae9784..f10e5cf6fd89 100644 --- a/tools/testing/selftests/bpf/progs/aggregate_ret_kfunc.c +++ b/tools/testing/selftests/bpf/progs/aggregate_ret_kfunc.c @@ -71,7 +71,7 @@ __naked int aggregate_ret_kfunc_fastcall_fail(void) =20 SEC("tc") __arch_x86_64 __arch_arm64 -__failure __msg("is not composed of scalars") +__failure __msg("is not composed of scalars or arena pointers") __naked int aggregate_ret_kfunc_ptr_fail(void) { asm volatile ( --=20 2.53.0-Meta