From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 60FC12517A8; Tue, 29 Apr 2025 18:16:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745950566; cv=none; b=I7TSn5cRqfUojnbX0qvX2nDwxWWMW3r8NCa6xRJ0QvCRqcVBI5TZS1vKwDJox3ftWnz2QjSHU9lzWWDB2cdXU/l27TM5G/zTqNK3ss281wVJRF/6VDEFpNK0kzkbXgqmfBl6ssl/636V6tONBLniVPLhZQnZVfTUZlvbSGkcbeg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745950566; c=relaxed/simple; bh=/U0NU/NV4B+0kILY+pWBLQr/ol1Q91mGEIPzk9yNmNs=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=HuHXVILQlJ6qPk71Sck7mpb6+bjYUyWy5E4GPRMlfrL0R9ICTqeQYqA4m9VeZtsKC4LNHefFEHtZJlfEm7xZo8okSd5msWx/aETHewtMhaTNnBsgQrqnJai2+jGKb3Fkn3pxLMjw/WMpZ4qHrXig9HWxsamajs78ZxgdWm234LI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=ygcUwpgl; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="ygcUwpgl" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D0DD9C4CEE3; Tue, 29 Apr 2025 18:16:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1745950566; bh=/U0NU/NV4B+0kILY+pWBLQr/ol1Q91mGEIPzk9yNmNs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ygcUwpgl84AOjBgb7377rydxtI4G9UaZk9HTfw9C248sKJ6CCTd16MZ3PAxjkaORR 8zpmJ0Ko98oBLCPp7VyGkP1jTOw0D9um1ynYYgjVsn2HDNBFxsHQZ6tq+mg3UK47IH 0+GJiWsftkVrMG+1RafqAhDJv2WfuH/6vQ4l52Vg= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Yafang Shao , Alexei Starovoitov , Sasha Levin Subject: [PATCH 6.6 128/204] bpf: Reject attaching fexit/fmod_ret to __noreturn functions Date: Tue, 29 Apr 2025 18:43:36 +0200 Message-ID: <20250429161104.668878672@linuxfoundation.org> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250429161059.396852607@linuxfoundation.org> References: <20250429161059.396852607@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Yafang Shao [ Upstream commit cfe816d469dce9c0864062cf65dd7b3c42adc6f8 ] If we attach fexit/fmod_ret to __noreturn functions, it will cause an issue that the bpf trampoline image will be left over even if the bpf link has been destroyed. Take attaching do_exit() with fexit for example. The fexit works as follows, bpf_trampoline + __bpf_tramp_enter + percpu_ref_get(&tr->pcref); + call do_exit() + __bpf_tramp_exit + percpu_ref_put(&tr->pcref); Since do_exit() never returns, the refcnt of the trampoline image is never decremented, preventing it from being freed. That can be verified with as follows, $ bpftool link show <<<< nothing output $ grep "bpf_trampoline_[0-9]" /proc/kallsyms ffffffffc04cb000 t bpf_trampoline_6442526459 [bpf] <<<< leftover In this patch, all functions annotated with __noreturn are rejected, except for the following cases: - Functions that result in a system reboot, such as panic, machine_real_restart and rust_begin_unwind - Functions that are never executed by tasks, such as rest_init and cpu_startup_entry - Functions implemented in assembly, such as rewind_stack_and_make_dead and xen_cpu_bringup_again, lack an associated BTF ID. With this change, attaching fexit probes to functions like do_exit() will be rejected. $ ./fexit libbpf: prog 'fexit': BPF program load failed: -EINVAL libbpf: prog 'fexit': -- BEGIN PROG LOAD LOG -- Attaching fexit/fmod_ret to __noreturn functions is rejected. Signed-off-by: Yafang Shao Link: https://lore.kernel.org/r/20250318114447.75484-2-laoar.shao@gmail.com Signed-off-by: Alexei Starovoitov Signed-off-by: Sasha Levin --- kernel/bpf/verifier.c | 32 ++++++++++++++++++++++++++++++++ 1 file changed, 32 insertions(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index d6a4102312fad..e443506b0a65a 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -20106,6 +20106,33 @@ BTF_ID(func, __rcu_read_unlock) #endif BTF_SET_END(btf_id_deny) +/* fexit and fmod_ret can't be used to attach to __noreturn functions. + * Currently, we must manually list all __noreturn functions here. Once a more + * robust solution is implemented, this workaround can be removed. + */ +BTF_SET_START(noreturn_deny) +#ifdef CONFIG_IA32_EMULATION +BTF_ID(func, __ia32_sys_exit) +BTF_ID(func, __ia32_sys_exit_group) +#endif +#ifdef CONFIG_KUNIT +BTF_ID(func, __kunit_abort) +BTF_ID(func, kunit_try_catch_throw) +#endif +#ifdef CONFIG_MODULES +BTF_ID(func, __module_put_and_kthread_exit) +#endif +#ifdef CONFIG_X86_64 +BTF_ID(func, __x64_sys_exit) +BTF_ID(func, __x64_sys_exit_group) +#endif +BTF_ID(func, do_exit) +BTF_ID(func, do_group_exit) +BTF_ID(func, kthread_complete_and_exit) +BTF_ID(func, kthread_exit) +BTF_ID(func, make_task_dead) +BTF_SET_END(noreturn_deny) + static bool can_be_sleepable(struct bpf_prog *prog) { if (prog->type == BPF_PROG_TYPE_TRACING) { @@ -20194,6 +20221,11 @@ static int check_attach_btf_id(struct bpf_verifier_env *env) } else if (prog->type == BPF_PROG_TYPE_TRACING && btf_id_set_contains(&btf_id_deny, btf_id)) { return -EINVAL; + } else if ((prog->expected_attach_type == BPF_TRACE_FEXIT || + prog->expected_attach_type == BPF_MODIFY_RETURN) && + btf_id_set_contains(&noreturn_deny, btf_id)) { + verbose(env, "Attaching fexit/fmod_ret to __noreturn functions is rejected.\n"); + return -EINVAL; } key = bpf_trampoline_compute_key(tgt_prog, prog->aux->attach_btf, btf_id); -- 2.39.5