From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (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 EC1D17F for ; Tue, 22 Aug 2023 02:37:33 +0000 (UTC) Received: from out-49.mta0.migadu.com (out-49.mta0.migadu.com [IPv6:2001:41d0:1004:224b::31]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 49951DB for ; Mon, 21 Aug 2023 19:37:32 -0700 (PDT) Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1692671850; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=qoRI/BqS2sTcItc+Iwy7Szi2M9Lr+00S851MrOeiuXY=; b=u4FDjbRwMAV/cbzsNL+NEPqNOYjrFeyYl6tQtlwwv5QBCgaK9OJgQtEiHHN19vp7zK3Ixe jkRt/qXwqOwiMv0llbVvX9HvHL8lvr2I6cB2kAMbvA6UIXvwF+6/Enjb3z7RdLUQU2eChW G9AUjE2BIPTEmzm6AOewqPI+mMWuM8w= Date: Mon, 21 Aug 2023 19:37:22 -0700 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Reply-To: yonghong.song@linux.dev Subject: Re: [PATCH v2 bpf-next 5/7] bpf: Consider non-owning refs to refcounted nodes RCU protected Content-Language: en-US To: Dave Marchevsky , bpf@vger.kernel.org Cc: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Kernel Team References: <20230821193311.3290257-1-davemarchevsky@fb.com> <20230821193311.3290257-6-davemarchevsky@fb.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Yonghong Song In-Reply-To: <20230821193311.3290257-6-davemarchevsky@fb.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_BLOCKED, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net On 8/21/23 12:33 PM, Dave Marchevsky wrote: > An earlier patch in the series ensures that the underlying memory of > nodes with bpf_refcount - which can have multiple owners - is not reused > until RCU grace period has elapsed. This prevents > use-after-free with non-owning references that may point to > recently-freed memory. While RCU read lock is held, it's safe to > dereference such a non-owning ref, as by definition RCU GP couldn't have > elapsed and therefore underlying memory couldn't have been reused. > > From the perspective of verifier "trustedness" non-owning refs to > refcounted nodes are now trusted only in RCU CS and therefore should no > longer pass is_trusted_reg, but rather is_rcu_reg. Let's mark them > MEM_RCU in order to reflect this new state. > > Signed-off-by: Dave Marchevsky > --- > include/linux/bpf.h | 3 ++- > kernel/bpf/verifier.c | 13 ++++++++++++- > 2 files changed, 14 insertions(+), 2 deletions(-) > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h > index eced6400f778..12596af59c00 100644 > --- a/include/linux/bpf.h > +++ b/include/linux/bpf.h > @@ -653,7 +653,8 @@ enum bpf_type_flag { > MEM_RCU = BIT(13 + BPF_BASE_TYPE_BITS), > > /* Used to tag PTR_TO_BTF_ID | MEM_ALLOC references which are non-owning. > - * Currently only valid for linked-list and rbtree nodes. > + * Currently only valid for linked-list and rbtree nodes. If the nodes > + * have a bpf_refcount_field, they must be tagged MEM_RCU as well. > */ > NON_OWN_REF = BIT(14 + BPF_BASE_TYPE_BITS), > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index 8db0afa5985c..55607ab30522 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -8013,6 +8013,7 @@ int check_func_arg_reg_off(struct bpf_verifier_env *env, > case PTR_TO_BTF_ID | PTR_TRUSTED: > case PTR_TO_BTF_ID | MEM_RCU: > case PTR_TO_BTF_ID | MEM_ALLOC | NON_OWN_REF: > + case PTR_TO_BTF_ID | MEM_ALLOC | NON_OWN_REF | MEM_RCU: > /* When referenced PTR_TO_BTF_ID is passed to release function, > * its fixed offset must be 0. In the other cases, fixed offset > * can be non-zero. This was already checked above. So pass > @@ -10479,6 +10480,7 @@ static int process_kf_arg_ptr_to_btf_id(struct bpf_verifier_env *env, > static int ref_set_non_owning(struct bpf_verifier_env *env, struct bpf_reg_state *reg) > { > struct bpf_verifier_state *state = env->cur_state; > + struct btf_record *rec = reg_btf_record(reg); > > if (!state->active_lock.ptr) { > verbose(env, "verifier internal error: ref_set_non_owning w/o active lock\n"); > @@ -10491,6 +10493,9 @@ static int ref_set_non_owning(struct bpf_verifier_env *env, struct bpf_reg_state > } > > reg->type |= NON_OWN_REF; > + if (rec->refcount_off >= 0) > + reg->type |= MEM_RCU; Should the above MEM_RCU marking be done unless reg access is in rcu critical section? I think we still have issues for state resetting with bpf_spin_unlock() and bpf_rcu_read_unlock(), both of which will try to convert the reg state to PTR_UNTRUSTED. Let us say reg state is PTR_TO_BTF_ID | MEM_ALLOC | NON_OWN_REF | MEM_RCU (1). If hitting bpf_spin_unlock(), since MEM_RCU is in the reg state, the state should become PTR_TO_BTF_ID | MEM_ALLOC | MEM_RCU some additional code might be needed so we wont have verifier complaints about ref_obj_id == 0. (2). If hitting bpf_rcu_read_unlock(), the state should become PTR_TO_BTF_ID | MEM_ALLOC | NON_OWN_REF since register access still in bpf_spin_lock() region. Does this make sense? > + > return 0; > } > > @@ -11328,6 +11333,11 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn, > struct bpf_func_state *state; > struct bpf_reg_state *reg; > > + if (in_rbtree_lock_required_cb(env) && (rcu_lock || rcu_unlock)) { > + verbose(env, "Calling bpf_rcu_read_{lock,unlock} in unnecessary rbtree callback\n"); > + return -EACCES; > + } > + > if (rcu_lock) { > verbose(env, "nested rcu read lock (kernel function %s)\n", func_name); > return -EINVAL; > @@ -16689,7 +16699,8 @@ static int do_check(struct bpf_verifier_env *env) > return -EINVAL; > } > > - if (env->cur_state->active_rcu_lock) { > + if (env->cur_state->active_rcu_lock && > + !in_rbtree_lock_required_cb(env)) { > verbose(env, "bpf_rcu_read_unlock is missing\n"); > return -EINVAL; > }