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 8BDD433065D for ; Thu, 27 Aug 2026 06:11:51 +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=1787811112; cv=none; b=bnke95L32YOuulD0bCTlxnZT9h5aGXscfcRIcpVWjhqBBU7FGiYdah0qAsote8CTXsXH5hzNq0z9d14puRM3Ux7uLsL4pvb3cJlq1y+tT5KCrUurZaqxxdXjOTnRcMyu7LwrSC41bie6Nnkw7hI8EDi9Q1rRrQ9EoqDUSieDe2s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787811112; c=relaxed/simple; bh=MAG7D/1GFdOJLqFTBjwiqaTsZ3x6SjNPDHYANQOvgZk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=J2gcOunNg2DeWH4wZ1TxwHOwCGNGx8oPG7nmdyYozdkVYbStttx50YipOYV69uBu+zKfC/gtaZqlMGfmiFYF6WljOXsars5rh98zORXnazYN9/HZexMsvdRWa7aDZDp6heHBmbaE57Vcrj1Hr5/AzFawqTNvb2r9WsoPpbt1gTA= 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 A3F4226CDEAAFD; Wed, 26 Aug 2026 23:11:45 -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 v3 06/11] bpf: Allow a global function to return arena pointers by value Date: Wed, 26 Aug 2026 23:11:45 -0700 Message-ID: <20260827061145.2517714-1-yonghong.song@linux.dev> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260827061114.2514603-1-yonghong.song@linux.dev> References: <20260827061114.2514603-1-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 global function may already return an arena pointer on its own, and check_global_ret_scalar_reg() accepts one in either half of the R0:R2 pair. Let the members of a by-value struct it returns be arena pointers as well, rather than scalars only. Signed-off-by: Yonghong Song --- kernel/bpf/btf.c | 20 ++++++++++++++----- .../selftests/bpf/progs/exceptions_fail.c | 2 +- 2 files changed, 16 insertions(+), 6 deletions(-) diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index b1f4ef614d4c..f6d82a8fd617 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -7973,13 +7973,22 @@ static int btf_validate_return_type(struct bpf_ve= rifier_env *env, struct btf *bt 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. + * scalar pair, so a pointer member would be laundered into a + * scalar and escape provenance and reference tracking. Only + * scalars and arena pointers are allowed: an arena pointer has + * no provenance to lose, since a program may already derive one + * from any scalar with addr_space_cast(), which confines the + * result to the arena. A local function is verified inline, so + * its caller receives the real register state and any member is + * fine. */ bool local_func =3D subprog && !is_global; + u32 member_kinds =3D BTF_MEMBER_SCALAR; =20 - if (local_func || btf_struct_is_composed_of(env, btf, t, BTF_MEMBER_SC= ALAR)) + if (subprog) + member_kinds |=3D BTF_MEMBER_ARENA_PTR; + + if (local_func || btf_struct_is_composed_of(env, btf, t, member_kinds)= ) return 0; } =20 @@ -8075,7 +8084,8 @@ int btf_prepare_func_args(struct bpf_verifier_env *= env, int subprog) if (is_global) { bpf_log(log, "Global function %s() has unsupported return type. " - "Only void, scalar, or a scalar-only struct/union up to 16 bytes is = supported.\n", + "Only void, a scalar, an arena pointer, or a struct/union of " + "scalars and arena pointers up to 16 bytes is supported.\n", tname); } return err; diff --git a/tools/testing/selftests/bpf/progs/exceptions_fail.c b/tools/= testing/selftests/bpf/progs/exceptions_fail.c index 9708efb93683..cde4982e9989 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("Only void, scalar, or a scalar-only struct/union up to = 16 bytes is supported.") +__failure __msg("Only void, a scalar, an arena pointer, or a struct/unio= n of scalars") int reject_exception_cb_type_1(struct __sk_buff *ctx) { bpf_throw(0); --=20 2.53.0-Meta