linux-kernel - Re: [PATCH 00/11] Introduce Simple atomic and non-atomic counters

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 for Android: free password hash cracker in your pocket

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

Message-ID: <202009260930.9252966D@keescook>
Date:   Sat, 26 Sep 2020 09:33:17 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Shuah Khan <skhan@...uxfoundation.org>
Cc:     corbet@....net, gregkh@...uxfoundation.org, shuah@...nel.org,
        rafael@...nel.org, johannes@...solutions.net, lenb@...nel.org,
        james.morse@....com, tony.luck@...el.com, bp@...en8.de,
        arve@...roid.com, tkjos@...roid.com, maco@...roid.com,
        joel@...lfernandes.org, christian@...uner.io, hridya@...gle.com,
        surenb@...gle.com, minyard@....org, arnd@...db.de,
        mchehab@...nel.org, rric@...nel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-acpi@...r.kernel.org, devel@...verdev.osuosl.org,
        openipmi-developer@...ts.sourceforge.net,
        linux-edac@...r.kernel.org
Subject: Re: [PATCH 00/11] Introduce Simple atomic and non-atomic counters

On Fri, Sep 25, 2020 at 06:13:37PM -0600, Shuah Khan wrote:
> On 9/25/20 5:52 PM, Kees Cook wrote:
> > On Fri, Sep 25, 2020 at 05:47:14PM -0600, Shuah Khan wrote:
> > > -- Addressed Kees's comments:
> > >     1. Non-atomic counters renamed to counter_simple32 and counter_simple64
> > >        to clearly indicate size.
> > >     2. Added warning for counter_simple* usage and it should be used only
> > >        when there is no need for atomicity.
> > >     3. Renamed counter_atomic to counter_atomic32 to clearly indicate size.
> > >     4. Renamed counter_atomic_long to counter_atomic64 and it now uses
> > >        atomic64_t ops and indicates size.
> > >     5. Test updated for the API renames.
> > >     6. Added helper functions for test results printing
> > >     7. Verified that the test module compiles in kunit env. and test
> > >        module can be loaded to run the test.
> > 
> > Thanks for all of this!
> > 
> > >     8. Updated Documentation to reflect the intent to make the API
> > >        restricted so it can never be used to guard object lifetimes
> > >        and state management. I left _return ops for now, inc_return
> > >        is necessary for now as per the discussion we had on this topic.
> > 
> > I still *really* do not want dec_return() to exist. That is asking for
> > trouble. I'd prefer inc_return() not exist either, but I can live with
> > it. ;)
> > 
> 
> Thanks. I am equally concerned about adding anything that can be used to
> guard object lifetimes. So I will make sure this set won't expand and
> plan to remove dec_return() if we don't find any usages.

I would like it much stronger than "if". dec_return() needs to be just
dec() and read(). It will not be less efficient (since they're both
inlines), but it _will_ create a case where the atomicity cannot be used
for ref counting. My point is that anything that _requires_ dec_return()
(or, frankly, inc_return()) is _not_ "just" a statistical counter. It
may not be a refcounter, but it relies on the inc/dec atomicity for some
reason beyond counting in once place and reporting it in another.

-- 
Kees Cook