From owner-freebsd-hackers Thu Feb 14 19:13:17 2002 Delivered-To: freebsd-hackers@freebsd.org Received: from hawk.mail.pas.earthlink.net (hawk.mail.pas.earthlink.net [207.217.120.22]) by hub.freebsd.org (Postfix) with ESMTP id 818CE37B439 for ; Thu, 14 Feb 2002 19:12:45 -0800 (PST) Received: from dialup-209.244.104.20.dial1.sanjose1.level3.net ([209.244.104.20] helo=mindspring.com) by hawk.mail.pas.earthlink.net with esmtp (Exim 3.33 #1) id 16bYni-0000z9-00; Thu, 14 Feb 2002 19:12:42 -0800 Message-ID: <3C6C7C9E.9E61C6D4@mindspring.com> Date: Thu, 14 Feb 2002 19:12:30 -0800 From: Terry Lambert X-Mailer: Mozilla 4.7 [en]C-CCK-MCD {Sony} (Win98; U) X-Accept-Language: en MIME-Version: 1.0 To: Jason Mawdsley Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: mmap and PROT_WRITE References: <05e201c1b5cb$73a00520$2a64a8c0@macadamian.com> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG Jason Mawdsley wrote: [ ... trying to distinguish between PROT_WRITE and PROT_READ|PROT_WRITE ... ] > Why can't I write to memory in the first case? > > Is there anyway I can implement writable but no readable memory? Yes. Use hardware manufactured by a vendor other than Intel, and which can support it. > I read some where that there is no true write only memory do to the > limitations of x86. Yes. And on 386, there's no write protection against protected mode writes at all, so you have to do dirty tricks to keep people from doing a "read" into a kernel address space in order to have the kernel. It's one of the reasons (besides /dev/slow^Wrandom) that the 386 is no longer supported in the GENERIC kernel. -- Terry To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message