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Message-ID: <20161003215739.GO14666@pc.thejh.net>
Date: Mon, 3 Oct 2016 23:57:40 +0200
From: Jann Horn <jann@...jh.net>
To: kernel-hardening@...ts.openwall.com
Cc: keescook@...omium.org, David Windsor <dwindsor@...il.com>,
Hans Liljestrand <ishkamiel@...il.com>,
Elena Reshetova <elena.reshetova@...el.com>
Subject: Re: [RFC PATCH 05/13] fs: identify wrapping
atomic usage
On Mon, Oct 03, 2016 at 09:41:18AM +0300, Elena Reshetova wrote:
> From: David Windsor <dwindsor@...il.com>
>
> In some cases atomic is not used for reference
> counting and therefore should be allowed to overflow.
> Identify such cases and make a switch to non-hardened
> atomic version.
Depending on what the overhead ends up being, it might make sense to opt
f_count in struct file out of the protection. It is the hottest user of
atomic_t/atomic_long_t that I know of (incremented and decremented for
every operation on a file descriptor in a multithreaded process), it is
64 bits wide and it's only incremented and decremented in steps of 1.
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