Date: Thu, 14 Feb 2002 19:12:30 -0800 From: Terry Lambert <tlambert2@mindspring.com> To: Jason Mawdsley <jason@macadamian.com> Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: mmap and PROT_WRITE Message-ID: <3C6C7C9E.9E61C6D4@mindspring.com> References: <05e201c1b5cb$73a00520$2a64a8c0@macadamian.com>
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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
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