linux-kernel - Re: [PATCH] nommu arch dont zero the anonymous mapping by adding UNINITIALIZE flag

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <6d6a94c50703300644y28e51f47h19182f550c18c40d@mail.gmail.com>
Date:	Fri, 30 Mar 2007 21:44:24 +0800
From:	"Aubrey Li" <aubreylee@...il.com>
To:	"David Howells" <dhowells@...hat.com>
Cc:	vapier.adi@...il.com, jie.zhang@...log.com, bryan.wu@...log.com,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nommu arch dont zero the anonymous mapping by adding UNINITIALIZE flag

On 3/30/07, David Howells <dhowells@...hat.com> wrote:
> Aubrey Li <aubreylee@...il.com> wrote:
>
> > malloc() allocates size bytes and returns a pointer to the allocated memory.
> > ****The memory is not cleared.****
>
> But this is *not* malloc().  It's mmap().  Are you prepared to guarantee that
> there are no applications out there that don't rely on anon mmap() giving
> zeroed memory?

I can't find mmap must give zeroed memory in the mmap manual.
Is there any reason relying on anon mmap() giving zerod memory?
Can you show me an example?

>
> The MMU-mode clearing is done for security reasons - there shouldn't be any
> leakage between processes, and because the zero page can just be faulted in.
>
NO-MMU can't do this clearing. Performance is down.

> Personally, I'd prefer to maintain compatibility with MMU-mode wherever
> possible, but I'm happy with overrides like the MAP_UNINITIALISED flag
> suggested.
>
Not necessary IMHO.

-Aubrey
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/