From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756554AbbJAJ3Z (ORCPT ); Thu, 1 Oct 2015 05:29:25 -0400 Received: from mail-wi0-f172.google.com ([209.85.212.172]:34844 "EHLO mail-wi0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752331AbbJAJ3T (ORCPT ); Thu, 1 Oct 2015 05:29:19 -0400 Date: Thu, 1 Oct 2015 11:29:14 +0200 From: Ingo Molnar To: Andrey Ryabinin Cc: Kees Cook , Thomas Gleixner , Andy Lutomirski , Dmitry Vyukov , Ingo Molnar , "H. Peter Anvin" , Andy Lutomirski , Borislav Petkov , Denys Vlasenko , "x86@kernel.org" , LKML , Kostya Serebryany , Alexander Potapenko , Andrey Konovalov , Sasha Levin , Andi Kleen , kasan-dev , Linus Torvalds , Peter Zijlstra , Andrew Morton , Al Viro Subject: Re: [PATCH v3] fs/proc, core/debug: Don't expose absolute kernel addresses via wchan Message-ID: <20151001092914.GC6543@gmail.com> References: <20150930071537.GA19048@gmail.com> <20150930135917.GA3285@gmail.com> <20151001075715.GA23430@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Andrey Ryabinin wrote: > 2015-10-01 10:57 GMT+03:00 Ingo Molnar : > > diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt > > index d411ca63c8b6..db64f7d6492d 100644 > > --- a/Documentation/filesystems/proc.txt > > +++ b/Documentation/filesystems/proc.txt > > @@ -140,7 +140,8 @@ Table 1-1: Process specific entries in /proc > > stat Process status > > statm Process memory status information > > status Process status in human readable form > > - wchan If CONFIG_KALLSYMS is set, a pre-decoded wchan > > + wchan If CONFIG_KALLSYMS=y, wchan (the kernel function the process is > > + blocked in) symbol string. "0" if not blocked or !KALLSYMS. > > /proc/PID/wchan is under #ifdef CONFIG_KALLSYMS. Yeah, indeed, so I clarified that text to now read: + wchan Present with CONFIG_KALLSYMS=y: it shows the kernel function + symbol the task is blocked in - or "0" if not blocked. > > diff --git a/fs/proc/base.c b/fs/proc/base.c > > index b25eee4cead5..6f05aabce3aa 100644 > > --- a/fs/proc/base.c > > +++ b/fs/proc/base.c > > @@ -430,13 +430,10 @@ static int proc_pid_wchan(struct seq_file *m, struct pid_namespace *ns, > > > > wchan = get_wchan(task); > > > > - if (lookup_symbol_name(wchan, symname) < 0) { > > - if (!ptrace_may_access(task, PTRACE_MODE_READ)) > > - return 0; > > - seq_printf(m, "%lu", wchan); > > - } else { > > + if (!lookup_symbol_name(wchan, symname)) > > seq_printf(m, "%s", symname); > > - } > > + else > > + seq_putc(m, '0'); > > Maybe we should respect 'kptr_restrict' sysctl when we use '%ps', '%pB' etc. > printk formats (AFAIK %ps just prints address if KALLSYMS=n, or lookup failed). > In that case you could just do 'seq_printf(m, "%ps", wchan)'. > > OTOH, %ps, %pS are used mostly in debugging, so investigating some crash in > production kernel with no !KALLSYMS and with kptr_restrict != 0 will be a > nightmare. So this code does not use %pX, it prints the symbol. Yes, the symbol in itself is 'information' about the execution of the task in itself - but /proc per se is all about providing information about tasks in the system (including to unprivileged users), so there's IMHO little point in restricting this output any further ... I think ktrp_restrict is mostly about not exposing absolute addresses. Thanks, Ingo