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 4638E204874; Fri, 4 Apr 2025 00:06:54 +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=1743725215; cv=none; b=cLqfmg8DdjbVCCUqOoD32dF9RfoGOaohnlvRWurIw70geOBDW7f2G9MpN9JMyjaq38a66fj2vBqKmXCbABRPZHo3/9sji4eEgkD+YBOpbYj8qvx+vZRpLyEtoZmEwW8+iJfTbHp9Y0QpweN3/rI/Am1LaN5rrl15A5E9LTcBea8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743725215; c=relaxed/simple; bh=kOpVAW2eZnPzGD/yiLTqH1fpEPle2cVcYhRZhQyftlE=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=d/qHNrhvz35dXVOWS7iWBM55yTXpNhJURAj0y91EnmFmqTSk6ruBfYivqUIpv8l31A5slw3a9Bs5cgotGHtz9vM+AwkQgDU/X8qe441acgp7/jI2BFxl2W9K2jv4Z1ZHoPito//3aD9+vsIL6YUME/BB2QLllz5yuOeB4cB2syc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Dt+AyTWX; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Dt+AyTWX" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B9E00C4CEE3; Fri, 4 Apr 2025 00:06:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1743725214; bh=kOpVAW2eZnPzGD/yiLTqH1fpEPle2cVcYhRZhQyftlE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Dt+AyTWXHOcPY+cuP5OAxNGas6Croxg+UOq9yWkHYZb7fzj5/LoqV6VQFiuTCtt9g +qa3Pek49V5iDPvkA9r1XV9kvtgP+4HRCLIA/D3VYFsB9Ovi1/mdoua6Xqs3gflinI y165ut7mMxifrTfOyB2Uc2rSQ/sVf26eAvxxoXsNpPIfhKgTvL2cR5kzMlESQiUzrt wuykMIzfHQKHmubc+sv8GuxhbfMAfT9ejVK3jt7lUFM1jgxiYs5WcCoGuJj+BlS97V 4OWe33kgkPg7UPR3Rvl/H6L0gCcnkt+me51oCbdRJ1MKUzgpPICYyU3Qx2zWtbH39S Xq/Q/pitKzslw== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Yafang Shao , Alexei Starovoitov , Sasha Levin , daniel@iogearbox.net, andrii@kernel.org, bpf@vger.kernel.org Subject: [PATCH AUTOSEL 6.6 13/16] bpf: Reject attaching fexit/fmod_ret to __noreturn functions Date: Thu, 3 Apr 2025 20:06:21 -0400 Message-Id: <20250404000624.2688940-13-sashal@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250404000624.2688940-1-sashal@kernel.org> References: <20250404000624.2688940-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 6.6.85 Content-Transfer-Encoding: 8bit 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