From owner-freebsd-current@FreeBSD.ORG Tue Sep 16 15:36:05 2008 Return-Path: Delivered-To: current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id C70F11065676 for ; Tue, 16 Sep 2008 15:36:05 +0000 (UTC) (envelope-from deischen@freebsd.org) Received: from mail.netplex.net (mail.netplex.net [204.213.176.10]) by mx1.freebsd.org (Postfix) with ESMTP id 6ADEF8FC19 for ; Tue, 16 Sep 2008 15:36:05 +0000 (UTC) (envelope-from deischen@freebsd.org) Received: from sea.ntplx.net (sea.ntplx.net [204.213.176.11]) by mail.netplex.net (8.14.3/8.14.3/NETPLEX) with ESMTP id m8GFa3UC005867; Tue, 16 Sep 2008 11:36:03 -0400 (EDT) X-Virus-Scanned: by AMaViS and Clam AntiVirus (mail.netplex.net) X-Greylist: Message whitelisted by DRAC access database, not delayed by milter-greylist-4.0 (mail.netplex.net [204.213.176.10]); Tue, 16 Sep 2008 11:36:03 -0400 (EDT) Date: Tue, 16 Sep 2008 11:36:03 -0400 (EDT) From: Daniel Eischen X-X-Sender: eischen@sea.ntplx.net To: Andrey Chernov In-Reply-To: <20080916150120.GA40087@nagual.pp.ru> Message-ID: References: <20080916140319.GA34447@nagual.pp.ru> <20080916144502.GA39765@nagual.pp.ru> <3bbf2fe10809160753o7e5e8a78q7c6bd44c02bfd5c2@mail.gmail.com> <20080916150120.GA40087@nagual.pp.ru> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Cc: Attilio Rao , current@freebsd.org Subject: Re: Is fork() hook ever possible? X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list Reply-To: Daniel Eischen List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 16 Sep 2008 15:36:05 -0000 On Tue, 16 Sep 2008, Andrey Chernov wrote: > On Tue, Sep 16, 2008 at 04:53:54PM +0200, Attilio Rao wrote: >> 2008/9/16, Andrey Chernov : >>> On Tue, Sep 16, 2008 at 03:38:16PM +0100, Bob Bishop wrote: >>> > Hi, >>> >>>> >>> > On 16 Sep 2008, at 15:03, Andrey Chernov wrote: >>> > >>> >> I need some sort of fork() hook to detect that pid is changed to re- >>> >> stir >>> >> ar4random() after that (in the child), simple flag variable with >>> >> child's pid is needed. >>> >> >>> >> Currently OpenBSD does almost that checking getpid() every time >>> >> arc4random() called, but it is very slow way to use getpid() syscall >>> >> repeatedly, about 12-15 times slower than just arc4random() without >>> >> getpid(). >>> >> >>> >> Any ideas? >>> > >>> >>>> How about something hacky using mmap()/minherit()? >>> >>> Could you please provide working low cost example to detect that we are in >>> the child (pid changed or something else)? Calling getpid() as OpenBSD >>> does definitely is very high cost. :( >> >> An idea would be to implement a shared page between process and system >> which exports such informations. >> I'm sure we have a SoC project (2007) implementing this and perforce >> branches for it, I'm just not sure how far it did end. > > Please keep in mind that the hook itself must be invisible to user > application, we have standard API only - fork() and arc4random() family, > no additional setup or functions are possible outside of existen API. I.e. > the low cost hack must be completely inside ether the fork() wrapper or > arc4random(). Well, you could speed up getpid() by having libc wrap all fork() variants. The idea is that getpid() would only call __sys_getpid() the first time it was called and then only after a fork(). It would return the saved process id for all other cases. This wouldn't work if the application made its own syscall without going through libc. The shared page between process and system has been tossed around before and would probably be more benficial. Having access to time without making a syscall would be nice. -- DE