Date: Fri, 29 Apr 2011 12:00:00 -0400 From: Bob Hall <rjhjr0@gmail.com> To: RW <rwmaillists@googlemail.com> Cc: freebsd-questions@freebsd.org Subject: Re: Password theft from memory? Message-ID: <20110429160000.GA10275@stainmore> In-Reply-To: <20110429015406.118fa49b@gumby.homeunix.com> References: <20110425175420.GA61811@stainmore> <20110425232908.4104e026@gumby.homeunix.com> <20110426025614.GA62745@stainmore> <20110426104151.596bcc19@gumby.homeunix.com> <BANLkTikQzhmyXkCeSzzG-o%2Bz0L3ohNt2YQ@mail.gmail.com> <20110427014554.1e4c5281@gumby.homeunix.com> <20110427095420.GA41208@kongemord.krig.net> <20110428001010.13a76d07@gumby.homeunix.com> <20110428171740.GA5840@stainmore> <20110429015406.118fa49b@gumby.homeunix.com>
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On Fri, Apr 29, 2011 at 01:54:06AM +0100, RW wrote: > On Thu, 28 Apr 2011 13:17:41 -0400 > Bob Hall <rjhjr0@gmail.com> wrote: > > > On Thu, Apr 28, 2011 at 12:10:10AM +0100, RW wrote: > > > I'm not saying that anonymous mappings used by malloc aren't > > > zero-filled, just that it's not mentioned anywhere in the mmap man > > > page. I think it's just taken as read. > > > > I just got what you're trying to say. Unfortunately, your quotes > > mislead me about what you were concerned about. You're right, the man > > page doesn't explicitly state whether anonymous mappings are zero > > filled or not. Since man pages prioritize concision, I would expect > > the page to explain how anonymous mappings are different from other > > mappings, but not how they are the same. > > but they aren't the same - that's what the quotes were about. Looking back, I don't see anything in your quotes that raises the issue of anonymous objects being used differently. > If the zero-filled extensions included whole pages that have the same > status as the rest of the mapping then it would be reasonable to infer > that anonymous mappings are similarly filled with zeroed-pages. > > What that man page is talking about is a small padding region at the > end of a file-backed mapping that isn't really intended for use and > presumably could get re-zeroed at any moment since it has no backing > store. It seems to me to be unreasonable to infer anything about > anonymous mappings from this. When an anonymous object first gets a pagein, it grabs a free page and zeros it. Generally, the virtual memory system fetches new pages from a cache of zeroed pages. In either case, pages are zeroed before a process gets access. This is part of the general background info on virtual memory and I wouldn't expect it to be documented in the mmap man page. Off topic, the maillist is apparently filtering out my posts. I've looked at the webpage on filtering and can't find anything that explains why I'm being filtered. I've tried posting from another system that I posted successfully from previously, but no success. I've tried googling and searching the mail archives for problems related to google mail, but nothing came up. If some mail expert can spot what's causing me to be blocked and let me know, I'd be grateful. > > > _______________________________________________ > freebsd-questions@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-questions > To unsubscribe, send any mail to "freebsd-questions-unsubscribe@freebsd.org"
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