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[2001:1ae9:1c2:4c00:726e:c10f:8833:ff22]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a868f48621esm127706966b.176.2024.08.22.07.22.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 22 Aug 2024 07:22:52 -0700 (PDT) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Thu, 22 Aug 2024 16:22:51 +0200 To: Andrii Nakryiko Cc: linux-trace-kernel@vger.kernel.org, peterz@infradead.org, oleg@redhat.com, rostedt@goodmis.org, mhiramat@kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, paulmck@kernel.org, willy@infradead.org, surenb@google.com, akpm@linux-foundation.org, linux-mm@kvack.org Subject: Re: [PATCH v3 04/13] uprobes: travers uprobe's consumer list locklessly under SRCU protection Message-ID: References: <20240813042917.506057-1-andrii@kernel.org> <20240813042917.506057-5-andrii@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240813042917.506057-5-andrii@kernel.org> On Mon, Aug 12, 2024 at 09:29:08PM -0700, Andrii Nakryiko wrote: SNIP > @@ -1125,18 +1103,31 @@ void uprobe_unregister(struct uprobe *uprobe, struct uprobe_consumer *uc) > int err; > > down_write(&uprobe->register_rwsem); > - if (WARN_ON(!consumer_del(uprobe, uc))) { > - err = -ENOENT; > - } else { > - err = register_for_each_vma(uprobe, NULL); > - /* TODO : cant unregister? schedule a worker thread */ > - if (unlikely(err)) > - uprobe_warn(current, "unregister, leaking uprobe"); > - } > + > + list_del_rcu(&uc->cons_node); hi, I'm using this patchset as base for my changes and stumbled on this today, I'm probably missing something, but should we keep the 'uprobe->consumer_rwsem' lock around the list_del_rcu? jirka > + err = register_for_each_vma(uprobe, NULL); > + > up_write(&uprobe->register_rwsem); > > - if (!err) > - put_uprobe(uprobe); > + /* TODO : cant unregister? schedule a worker thread */ > + if (unlikely(err)) { > + uprobe_warn(current, "unregister, leaking uprobe"); > + goto out_sync; > + } > + > + put_uprobe(uprobe); > + > +out_sync: > + /* > + * Now that handler_chain() and handle_uretprobe_chain() iterate over > + * uprobe->consumers list under RCU protection without holding > + * uprobe->register_rwsem, we need to wait for RCU grace period to > + * make sure that we can't call into just unregistered > + * uprobe_consumer's callbacks anymore. If we don't do that, fast and > + * unlucky enough caller can free consumer's memory and cause > + * handler_chain() or handle_uretprobe_chain() to do an use-after-free. > + */ > + synchronize_srcu(&uprobes_srcu); > } > EXPORT_SYMBOL_GPL(uprobe_unregister); > > @@ -1214,13 +1205,20 @@ EXPORT_SYMBOL_GPL(uprobe_register); > int uprobe_apply(struct uprobe *uprobe, struct uprobe_consumer *uc, bool add) > { > struct uprobe_consumer *con; > - int ret = -ENOENT; > + int ret = -ENOENT, srcu_idx; > > down_write(&uprobe->register_rwsem); > - for (con = uprobe->consumers; con && con != uc ; con = con->next) > - ; > - if (con) > - ret = register_for_each_vma(uprobe, add ? uc : NULL); > + > + srcu_idx = srcu_read_lock(&uprobes_srcu); > + list_for_each_entry_srcu(con, &uprobe->consumers, cons_node, > + srcu_read_lock_held(&uprobes_srcu)) { > + if (con == uc) { > + ret = register_for_each_vma(uprobe, add ? uc : NULL); > + break; > + } > + } > + srcu_read_unlock(&uprobes_srcu, srcu_idx); > + > up_write(&uprobe->register_rwsem); > > return ret; > @@ -2085,10 +2083,12 @@ static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs) > struct uprobe_consumer *uc; > int remove = UPROBE_HANDLER_REMOVE; > bool need_prep = false; /* prepare return uprobe, when needed */ > + bool has_consumers = false; > > - down_read(&uprobe->register_rwsem); > current->utask->auprobe = &uprobe->arch; > - for (uc = uprobe->consumers; uc; uc = uc->next) { > + > + list_for_each_entry_srcu(uc, &uprobe->consumers, cons_node, > + srcu_read_lock_held(&uprobes_srcu)) { > int rc = 0; > > if (uc->handler) { > @@ -2101,17 +2101,24 @@ static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs) > need_prep = true; > > remove &= rc; > + has_consumers = true; > } > current->utask->auprobe = NULL; > > if (need_prep && !remove) > prepare_uretprobe(uprobe, regs); /* put bp at return */ > > - if (remove && uprobe->consumers) { > - WARN_ON(!uprobe_is_active(uprobe)); > - unapply_uprobe(uprobe, current->mm); > + if (remove && has_consumers) { > + down_read(&uprobe->register_rwsem); > + > + /* re-check that removal is still required, this time under lock */ > + if (!filter_chain(uprobe, current->mm)) { > + WARN_ON(!uprobe_is_active(uprobe)); > + unapply_uprobe(uprobe, current->mm); > + } > + > + up_read(&uprobe->register_rwsem); > } > - up_read(&uprobe->register_rwsem); > } > > static void > @@ -2119,13 +2126,15 @@ handle_uretprobe_chain(struct return_instance *ri, struct pt_regs *regs) > { > struct uprobe *uprobe = ri->uprobe; > struct uprobe_consumer *uc; > + int srcu_idx; > > - down_read(&uprobe->register_rwsem); > - for (uc = uprobe->consumers; uc; uc = uc->next) { > + srcu_idx = srcu_read_lock(&uprobes_srcu); > + list_for_each_entry_srcu(uc, &uprobe->consumers, cons_node, > + srcu_read_lock_held(&uprobes_srcu)) { > if (uc->ret_handler) > uc->ret_handler(uc, ri->func, regs); > } > - up_read(&uprobe->register_rwsem); > + srcu_read_unlock(&uprobes_srcu, srcu_idx); > } > > static struct return_instance *find_next_ret_chain(struct return_instance *ri) > -- > 2.43.5 >