Skip site navigation (1)Skip section navigation (2)
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>

next in thread | previous in thread | raw e-mail | index | archive | help
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




Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?3C6C7C9E.9E61C6D4>