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Mon, 24 Feb 2025 03:46:28 -0800 (PST) Received: from localhost.localdomain ([39.144.45.6]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-7325f063782sm18095080b3a.148.2025.02.24.03.46.20 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Mon, 24 Feb 2025 03:46:27 -0800 (PST) From: Yafang Shao To: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, song@kernel.org, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, jpoimboe@kernel.org, peterz@infradead.org Cc: bpf@vger.kernel.org, Yafang Shao Subject: [PATCH v3 1/2] bpf: Reject attaching fexit to functions annotated with __noreturn Date: Mon, 24 Feb 2025 19:46:05 +0800 Message-Id: <20250224114606.3500-2-laoar.shao@gmail.com> X-Mailer: git-send-email 2.37.1 (Apple Git-137.1) In-Reply-To: <20250224114606.3500-1-laoar.shao@gmail.com> References: <20250224114606.3500-1-laoar.shao@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Patchwork-Delegate: bpf@iogearbox.net If we attach fexit to a function annotated with __noreturn, 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() 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 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 to __noreturn functions is rejected. Signed-off-by: Yafang Shao --- kernel/bpf/verifier.c | 57 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 57 insertions(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 9971c03adfd5..6b0d3ed7dbd9 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -22841,6 +22841,59 @@ BTF_ID(func, __rcu_read_unlock) #endif BTF_SET_END(btf_id_deny) +/* Functions annotated with __noreturn are denied. Currently, we must manually + * list all __noreturn functions here. Once a more robust solution is + * implemented, this workaround can be removed. + */ +BTF_SET_START(fexit_deny) +#define NORETURN(fn) BTF_ID(func, fn) +NORETURN(__fortify_panic) +NORETURN(__ia32_sys_exit) +NORETURN(__ia32_sys_exit_group) +NORETURN(__kunit_abort) +NORETURN(__module_put_and_kthread_exit) +NORETURN(__stack_chk_fail) +NORETURN(__tdx_hypercall_failed) +NORETURN(__ubsan_handle_builtin_unreachable) +NORETURN(__x64_sys_exit) +NORETURN(__x64_sys_exit_group) +NORETURN(arch_cpu_idle_dead) +NORETURN(bch2_trans_in_restart_error) +NORETURN(bch2_trans_restart_error) +NORETURN(bch2_trans_unlocked_error) +NORETURN(cpu_bringup_and_idle) +NORETURN(cpu_startup_entry) +NORETURN(do_exit) +NORETURN(do_group_exit) +NORETURN(do_task_dead) +NORETURN(ex_handler_msr_mce) +NORETURN(hlt_play_dead) +NORETURN(hv_ghcb_terminate) +NORETURN(kthread_complete_and_exit) +NORETURN(kthread_exit) +NORETURN(kunit_try_catch_throw) +NORETURN(machine_real_restart) +NORETURN(make_task_dead) +NORETURN(mpt_halt_firmware) +NORETURN(nmi_panic_self_stop) +NORETURN(panic) +NORETURN(panic_smp_self_stop) +NORETURN(rest_init) +NORETURN(rewind_stack_and_make_dead) +NORETURN(rust_begin_unwind) +NORETURN(rust_helper_BUG) +NORETURN(sev_es_terminate) +NORETURN(snp_abort) +NORETURN(start_kernel) +NORETURN(stop_this_cpu) +NORETURN(usercopy_abort) +NORETURN(x86_64_start_kernel) +NORETURN(x86_64_start_reservations) +NORETURN(xen_cpu_bringup_again) +NORETURN(xen_start_kernel) +#undef NORETURN +BTF_SET_END(fexit_deny) + static bool can_be_sleepable(struct bpf_prog *prog) { if (prog->type == BPF_PROG_TYPE_TRACING) { @@ -22929,6 +22982,10 @@ 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 && + btf_id_set_contains(&fexit_deny, btf_id)) { + verbose(env, "Attaching fexit to __noreturn functions is rejected.\n"); + return -EINVAL; } key = bpf_trampoline_compute_key(tgt_prog, prog->aux->attach_btf, btf_id);