linux-kernel - Re: [PATCH 2/2] perf_counter: optimize context switch between identical inherited contexts

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: <20090522085716.GB13482@elte.hu>
Date:	Fri, 22 May 2009 10:57:16 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Paul Mackerras <paulus@...ba.org>, linux-kernel@...r.kernel.org,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 2/2] perf_counter: optimize context switch between
	identical inherited contexts


* Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:

> On Fri, 2009-05-22 at 14:27 +1000, Paul Mackerras wrote:
> 
> > The equivalence of contexts is detected by keeping a pointer in
> > each cloned context pointing to the context it was cloned from.
> > To cope with the situation where a context is changed by adding
> > or removing counters after it has been cloned, we also keep a
> > generation number on each context which is incremented every time
> > a context is changed.  When a context is cloned we take a copy
> > of the parent's generation number, and two cloned contexts are
> > equivalent only if they have the same parent and the same
> > generation number.  In order that the parent context pointer
> > remains valid (and is not reused), we increment the parent
> > context's reference count for each context cloned from it.
> 
> > +	u32			generation;
> 
> Suppose someone writes a malicious proglet that inherits the 
> counters, puts the child to sleep, does 2^32 mods on the counter 
> set, and then wakes up the child.
> 
> Would that merely corrupt the results, or make the kernel explode?

i think it should be an u64.

	Ingo
--
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/