Date: Sat, 10 Mar 2012 16:36:12 -0800 From: Linus Torvalds <torvalds@...ux-foundation.org> To: Djalal Harouni <tixxdz@...ndz.org> Cc: linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com, Andrew Morton <akpm@...ux-foundation.org>, Al Viro <viro@...iv.linux.org.uk>, Alexey Dobriyan <adobriyan@...il.com>, "Eric W. Biederman" <ebiederm@...ssion.com>, Vasiliy Kulikov <segoon@...nwall.com>, Kees Cook <keescook@...omium.org>, Solar Designer <solar@...nwall.com>, WANG Cong <xiyou.wangcong@...il.com>, James Morris <james.l.morris@...cle.com>, Oleg Nesterov <oleg@...hat.com>, linux-security-module@...r.kernel.org, linux-fsdevel@...r.kernel.org, Alan Cox <alan@...rguk.ukuu.org.uk>, Greg KH <gregkh@...uxfoundation.org>, Ingo Molnar <mingo@...e.hu>, Stephen Wilson <wilsons@...rt.ca>, "Jason A. Donenfeld" <Jason@...c4.com> Subject: Re: [PATCH 1/9] exec: add a global execve counter On Sat, Mar 10, 2012 at 4:12 PM, Linus Torvalds <torvalds@...ux-foundation.org> wrote: > > I wonder if we couldn't make something much cheaper, since we don't > actually care about it being globally incrementing, we just care about > it being globally unique. Actually, we don't even need it to be "globally unique" afaik. It really needs to be "relatively unique", since it's always compared within the confines of a particular task. So the problem with using the existing "self_exec_id" is that it's trivially the same across tasks. But a *tuple* of <struct task_struct, thread-specific exec_id> doesn't have that issue, so as far as I can tell we could easily make *that* the unique ID. I wonder if the number part of exec_id would even have to be 64-bit. I think I can do about 10000 execves per second if I make the program a small static one - and that's on a fast CPU. And it's a per-thread counter, so you can't scale it with lots of CPU's. So it would take something like four days to wrap. Hmm.. Linus
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