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 7F3351F3BB4; Fri, 4 Apr 2025 00:05:35 +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=1743725135; cv=none; b=BQQs0Ojz+iFK+yzEZIbf0FWVFxg+Sbs5cPk7+n6fyroBYnh3bEwiB4rGJGUFTydj/ISm1sEM0q3hJUeX0DT0Z/sroR9sg3dlysTqlM3n8m6cffdB390/X1op+0OGGBGOSza2oWFEfRjz9ckjvQx5YvSVyVa0BBsWQBGQu0pQETo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743725135; c=relaxed/simple; bh=38fLqJBtffkMwRhja1upZiM9/ny/+4wXtzf84gyInWE=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=ZFTOF+RvuMKWsIuCefQGyA7Y7GwrPw4rK0bx0Kw2upLSGU9O7aSXS0wRZ1gY9B4zOpFtmL4NThN2u3GPiCIJlJxkYLsdpNzrOOT99/3VvDXvIqEK5ZtTcJGVcWadGf28metsMY97p/YAaqc27SetfgraeJ2/ddMdMomn8nUsG9o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=sKRFmwuI; 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="sKRFmwuI" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 74EFBC4CEE9; Fri, 4 Apr 2025 00:05:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1743725135; bh=38fLqJBtffkMwRhja1upZiM9/ny/+4wXtzf84gyInWE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=sKRFmwuIrq3zEOeAKcHEHGqtw1wpF8ITu4UUf7EvZ6YrdrKbZs7nPbNz19xKXmGL+ QsRAdlwHr/qrrCsu+471hdJfMKN8XmSet71ivxbqDX8APEZUfKfB+jx11G/Qfpov5H iccPkvS59pBBWDfxc0QQRzKdWZmjQTO/fXvdJ3tuLisSs/jfUt4QPc6BarFxhRuxiA Lnls2CXUPpdF+9hdT6OR/2IOcuBVBQxcXnR4zAaRRKiVxbpjwXeVh7/tL7PfDv0YJx CEaN+RIq35JBU8l2WOCDOJXKbZMKqLsWocYMBGiSlk9LjkmtZ8WwSf/s2wLBWq9Lv0 n5e7md1geAN3Q== 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 6.13 19/22] bpf: Reject attaching fexit/fmod_ret to __noreturn functions Date: Thu, 3 Apr 2025 20:04:48 -0400 Message-Id: <20250404000453.2688371-19-sashal@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250404000453.2688371-1-sashal@kernel.org> References: <20250404000453.2688371-1-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 6.13.9 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 4f02345b764fd..3949fcf14b743 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -22431,6 +22431,33 @@ 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) { @@ -22519,6 +22546,11 @@ 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