From patchwork Mon Apr 8 08:09:28 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Benjamin Tissoires X-Patchwork-Id: 13620715 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 32B622E400; Mon, 8 Apr 2024 08:10:02 +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=1712563803; cv=none; b=o4Dcp7Y1Kqau+zrPog1BFm1N6oC04IKHqGGmgOue8QUW+1EqxsJc8EyiXPDB+JHiwP2RVtDdeuiqxRq2CO79K28AQRs9/LKuBsqakcp89Otin9piDy20H5u5d8hEuGYU2q/y6yYNL8OrGbt0ZFeFV5ustFbnolSWDs7hthlVPtg= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712563803; c=relaxed/simple; bh=pO/fOe12LlMwxLdSxFu7PL1Eaf6knBl1c2DD4TVRdco=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=kMyeFoCVAQ2Qu1QovoPjN9Ev/7m+p5opWfr/yxzJdPXHTIyPatyIn5TE5JmZPIUfaM4hwcz/UeYjrUi9jC5xMHAjgcveWTTG5lQmwaFgfsDfJHPaMSjtdagFmyd0CnM4y6xqHye8Q+1ZZZ/JE1JE+OcyYVkD5BO/2jUDcu2IGN8= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Trto9DYG; 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="Trto9DYG" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 625DCC433A6; Mon, 8 Apr 2024 08:09:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1712563802; bh=pO/fOe12LlMwxLdSxFu7PL1Eaf6knBl1c2DD4TVRdco=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=Trto9DYGhWXG/JLpCFHG6TGltcB581TEuGaOYPozPaJCgLyAlPkG2OLzTW2vw0Pbt oBKv13C1sb1m8iWJTZ/Blhzcm3db+4R1lbKA77mmFtAb+QkoPPbFnWFGlyTvap2gVS Z4JmGFsVLVL7Xio3G+91EvnSEzIcYQYrOh4u3Ha/Yr6gCsutRE/p0kI5NukP5zCS0s eEjRNBoqBgKCPboe2d1ckrIkIPNFqr41iJR9HORUTvd7xKlcBhF1GN2GienMgDy2tR fCcYL/3z9wfFahnQU8S/oudKn9twbtMfH7HNZPAJyIWmNDt+zMAS1/GK7P414PXIkT 94cT+xWC/Gxpg== From: Benjamin Tissoires Date: Mon, 08 Apr 2024 10:09:28 +0200 Subject: [PATCH RFC bpf-next v6 3/6] bpf/helpers: introduce bpf_timer_set_sleepable_cb() kfunc Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: <20240408-hid-bpf-sleepable-v6-3-0499ddd91b94@kernel.org> References: <20240408-hid-bpf-sleepable-v6-0-0499ddd91b94@kernel.org> In-Reply-To: <20240408-hid-bpf-sleepable-v6-0-0499ddd91b94@kernel.org> To: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , Mykola Lysenko , Shuah Khan Cc: Benjamin Tissoires , bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org X-Mailer: b4 0.12.4 X-Developer-Signature: v=1; a=ed25519-sha256; t=1712563787; l=9197; i=bentiss@kernel.org; s=20230215; h=from:subject:message-id; bh=pO/fOe12LlMwxLdSxFu7PL1Eaf6knBl1c2DD4TVRdco=; b=IXPAZPz6EQvhVIknWcnLDykM+Cc6wqGHJ6/L1lG2uPZeG23G0tNmwC/AGXyqTiOcFSwug7SQY vMFkj+BmaGFBh+yhGLM/VMALme0OsxII3/d7/2CYoVTKph2yP0jE22M X-Developer-Key: i=bentiss@kernel.org; a=ed25519; pk=7D1DyAVh6ajCkuUTudt/chMuXWIJHlv2qCsRkIizvFw= In this patch, bpf_timer_set_sleepable_cb() is functionally equivalent to bpf_timer_set_callback(), to the exception that it enforces the timer to be started with BPF_F_TIMER_SLEEPABLE. But given that bpf_timer_set_callback() is a helper when bpf_timer_set_sleepable_cb() is a kfunc, we need to teach the verifier about its attached callback. Marking that callback as sleepable will be done in a separate patch Acked-by: Eduard Zingerman Signed-off-by: Benjamin Tissoires --- changes in v6: - adapted for flags being set during timer_init changes in v5: - enforced sleepable timers to only have BPF_F_TIMER_SLEEPABLE - use is_bpf_timer_set_sleepable_cb_impl_kfunc() instead of generic is_async_cb() changes in v4: - added a new (ignored) argument to the kfunc so that we do not need to wlak the stack new in v3 (split from v2 02/10) --- kernel/bpf/helpers.c | 43 ++++++++++++++++++++++++++++++++++-- kernel/bpf/verifier.c | 60 +++++++++++++++++++++++++++++++++++++++++++++++++-- 2 files changed, 99 insertions(+), 4 deletions(-) diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index fd05d4358b31..d6528359b3f4 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -1291,8 +1291,8 @@ static const struct bpf_func_proto bpf_timer_init_proto = { .arg3_type = ARG_ANYTHING, }; -BPF_CALL_3(bpf_timer_set_callback, struct bpf_timer_kern *, timer, void *, callback_fn, - struct bpf_prog_aux *, aux) +static int __bpf_timer_set_callback(struct bpf_timer_kern *timer, void *callback_fn, + struct bpf_prog_aux *aux, bool is_sleepable) { struct bpf_prog *prev, *prog = aux->prog; struct bpf_hrtimer *t; @@ -1306,6 +1306,10 @@ BPF_CALL_3(bpf_timer_set_callback, struct bpf_timer_kern *, timer, void *, callb ret = -EINVAL; goto out; } + if (!!(t->flags & BPF_F_TIMER_SLEEPABLE) != is_sleepable) { + ret = -EINVAL; + goto out; + } if (!atomic64_read(&t->map->usercnt)) { /* maps with timers must be either held by user space * or pinned in bpffs. Otherwise timer might still be @@ -1336,6 +1340,12 @@ BPF_CALL_3(bpf_timer_set_callback, struct bpf_timer_kern *, timer, void *, callb return ret; } +BPF_CALL_3(bpf_timer_set_callback, struct bpf_timer_kern *, timer, void *, callback_fn, + struct bpf_prog_aux *, aux) +{ + return __bpf_timer_set_callback(timer, callback_fn, aux, false); +} + static const struct bpf_func_proto bpf_timer_set_callback_proto = { .func = bpf_timer_set_callback, .gpl_only = true, @@ -2650,6 +2660,34 @@ __bpf_kfunc void bpf_throw(u64 cookie) WARN(1, "A call to BPF exception callback should never return\n"); } +/** + * bpf_timer_set_sleepable_cb_impl() - Configure the timer to call %callback_fn + * static function in a sleepable context. + * @timer: The bpf_timer that needs to be configured + * @callback_fn: a static bpf function + * + * @returns %0 on success. %-EINVAL if %timer was not initialized with + * bpf_timer_init() earlier. %-EPERM if %timer is in a map that doesn't + * have any user references. + * The user space should either hold a file descriptor to a map with timers + * or pin such map in bpffs. When map is unpinned or file descriptor is + * closed all timers in the map will be cancelled and freed. + * + * This kfunc is equivalent to %bpf_timer_set_callback except that it tells + * the verifier that the target callback is run in a sleepable context. + */ +__bpf_kfunc int bpf_timer_set_sleepable_cb_impl(struct bpf_timer_kern *timer, + int (callback_fn)(void *map, int *key, struct bpf_timer *timer), + void *aux__ign) +{ + struct bpf_prog_aux *aux = (struct bpf_prog_aux *)aux__ign; + + if (!aux) + return -EINVAL; + + return __bpf_timer_set_callback(timer, (void *)callback_fn, aux, true); +} + __bpf_kfunc_end_defs(); BTF_KFUNCS_START(generic_btf_ids) @@ -2726,6 +2764,7 @@ BTF_ID_FLAGS(func, bpf_dynptr_is_null) BTF_ID_FLAGS(func, bpf_dynptr_is_rdonly) BTF_ID_FLAGS(func, bpf_dynptr_size) BTF_ID_FLAGS(func, bpf_dynptr_clone) +BTF_ID_FLAGS(func, bpf_timer_set_sleepable_cb_impl) BTF_KFUNCS_END(common_btf_ids) static const struct btf_kfunc_id_set common_kfunc_set = { diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index ccfe9057d8dc..00ac3a3a5f01 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -501,8 +501,12 @@ static bool is_dynptr_ref_function(enum bpf_func_id func_id) } static bool is_sync_callback_calling_kfunc(u32 btf_id); +static bool is_async_callback_calling_kfunc(u32 btf_id); +static bool is_callback_calling_kfunc(u32 btf_id); static bool is_bpf_throw_kfunc(struct bpf_insn *insn); +static bool is_bpf_timer_set_sleepable_cb_impl_kfunc(u32 btf_id); + static bool is_sync_callback_calling_function(enum bpf_func_id func_id) { return func_id == BPF_FUNC_for_each_map_elem || @@ -530,7 +534,8 @@ static bool is_sync_callback_calling_insn(struct bpf_insn *insn) static bool is_async_callback_calling_insn(struct bpf_insn *insn) { - return bpf_helper_call(insn) && is_async_callback_calling_function(insn->imm); + return (bpf_helper_call(insn) && is_async_callback_calling_function(insn->imm)) || + (bpf_pseudo_kfunc_call(insn) && is_async_callback_calling_kfunc(insn->imm)); } static bool is_may_goto_insn(struct bpf_insn *insn) @@ -9475,7 +9480,7 @@ static int push_callback_call(struct bpf_verifier_env *env, struct bpf_insn *ins */ env->subprog_info[subprog].is_cb = true; if (bpf_pseudo_kfunc_call(insn) && - !is_sync_callback_calling_kfunc(insn->imm)) { + !is_callback_calling_kfunc(insn->imm)) { verbose(env, "verifier bug: kfunc %s#%d not marked as callback-calling\n", func_id_name(insn->imm), insn->imm); return -EFAULT; @@ -10984,6 +10989,7 @@ enum special_kfunc_type { KF_bpf_percpu_obj_drop_impl, KF_bpf_throw, KF_bpf_iter_css_task_new, + KF_bpf_timer_set_sleepable_cb_impl, }; BTF_SET_START(special_kfunc_set) @@ -11010,6 +11016,7 @@ BTF_ID(func, bpf_throw) #ifdef CONFIG_CGROUPS BTF_ID(func, bpf_iter_css_task_new) #endif +BTF_ID(func, bpf_timer_set_sleepable_cb_impl) BTF_SET_END(special_kfunc_set) BTF_ID_LIST(special_kfunc_list) @@ -11040,6 +11047,7 @@ BTF_ID(func, bpf_iter_css_task_new) #else BTF_ID_UNUSED #endif +BTF_ID(func, bpf_timer_set_sleepable_cb_impl) static bool is_kfunc_ret_null(struct bpf_kfunc_call_arg_meta *meta) { @@ -11368,12 +11376,28 @@ static bool is_sync_callback_calling_kfunc(u32 btf_id) return btf_id == special_kfunc_list[KF_bpf_rbtree_add_impl]; } +static bool is_async_callback_calling_kfunc(u32 btf_id) +{ + return btf_id == special_kfunc_list[KF_bpf_timer_set_sleepable_cb_impl]; +} + static bool is_bpf_throw_kfunc(struct bpf_insn *insn) { return bpf_pseudo_kfunc_call(insn) && insn->off == 0 && insn->imm == special_kfunc_list[KF_bpf_throw]; } +static bool is_bpf_timer_set_sleepable_cb_impl_kfunc(u32 btf_id) +{ + return btf_id == special_kfunc_list[KF_bpf_timer_set_sleepable_cb_impl]; +} + +static bool is_callback_calling_kfunc(u32 btf_id) +{ + return is_sync_callback_calling_kfunc(btf_id) || + is_async_callback_calling_kfunc(btf_id); +} + static bool is_rbtree_lock_required_kfunc(u32 btf_id) { return is_bpf_rbtree_api_kfunc(btf_id); @@ -12157,6 +12181,16 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn, } } + if (is_bpf_timer_set_sleepable_cb_impl_kfunc(meta.func_id)) { + err = push_callback_call(env, insn, insn_idx, meta.subprogno, + set_timer_callback_state); + if (err) { + verbose(env, "kfunc %s#%d failed callback verification\n", + func_name, meta.func_id); + return err; + } + } + rcu_lock = is_kfunc_bpf_rcu_read_lock(&meta); rcu_unlock = is_kfunc_bpf_rcu_read_unlock(&meta); @@ -19559,6 +19593,28 @@ static int fixup_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn, desc->func_id == special_kfunc_list[KF_bpf_rdonly_cast]) { insn_buf[0] = BPF_MOV64_REG(BPF_REG_0, BPF_REG_1); *cnt = 1; + } else if (is_bpf_timer_set_sleepable_cb_impl_kfunc(desc->func_id)) { + /* The verifier will process callback_fn as many times as necessary + * with different maps and the register states prepared by + * set_timer_callback_state will be accurate. + * + * The following use case is valid: + * map1 is shared by prog1, prog2, prog3. + * prog1 calls bpf_timer_init for some map1 elements + * prog2 calls bpf_timer_set_callback for some map1 elements. + * Those that were not bpf_timer_init-ed will return -EINVAL. + * prog3 calls bpf_timer_start for some map1 elements. + * Those that were not both bpf_timer_init-ed and + * bpf_timer_set_callback-ed will return -EINVAL. + */ + struct bpf_insn ld_addrs[2] = { + BPF_LD_IMM64(BPF_REG_3, (long)env->prog->aux), + }; + + insn_buf[0] = ld_addrs[0]; + insn_buf[1] = ld_addrs[1]; + insn_buf[2] = *insn; + *cnt = 3; } return 0; }