linux-kernel - Re: [PATCH v4 3/7] regulator: IRQ based event/error notification helpers

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Date:   Wed, 7 Apr 2021 15:50:15 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     "Vaittinen, Matti" <Matti.Vaittinen@...rohmeurope.com>,
        Kees Cook <keescook@...omium.org>
Cc:     "agross@...nel.org" <agross@...nel.org>,
        "broonie@...nel.org" <broonie@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        linux-power <linux-power@...rohmeurope.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>,
        "linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
        "bjorn.andersson@...aro.org" <bjorn.andersson@...aro.org>,
        "lgirdwood@...il.com" <lgirdwood@...il.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>
Subject: Re: [PATCH v4 3/7] regulator: IRQ based event/error notification helpers

On Wed, Apr 7, 2021 at 12:49 PM Vaittinen, Matti
<Matti.Vaittinen@...rohmeurope.com> wrote:
> On Wed, 2021-04-07 at 12:10 +0300, Andy Shevchenko wrote:
> > On Wed, Apr 7, 2021 at 8:02 AM Matti Vaittinen
> > <matti.vaittinen@...rohmeurope.com> wrote:
> > > On Wed, 2021-04-07 at 01:44 +0300, Andy Shevchenko wrote:
> > > > On Tuesday, April 6, 2021, Matti Vaittinen <
> > > > matti.vaittinen@...rohmeurope.com> wrote:

Kees, there are two non-security guys discussing potential security
matters. Perhaps you may shed a light on this and tell which of our
stuff is risky and which is not and your recommendations on it.

> > > > > +       pr_emerg(msg);
> > > >
> > > > Oh là là, besides build bot complaints, this has serious security
> > > > implications. Never do like this.
> > >
> > > I'm not even trying to claim that was correct. And I did send a
> > > fixup -
> > > sorry for this. I don't intend to do this again.
> > >
> > > Now, when this is said - If you have a minute, please educate me.
> > > Assuming we know all the callers and that all the callers use this
> > > as
> > >
> > > die_loudly("foobarfoo\n");
> > > - what is the exploit mechanism?
> >
> > Not a security guy, but my understanding is that this code may be
> > used
> > as a gadget in ROP technique of attacks.
>
> Thanks Andy. It'd be interesting to learn more details as I am not a
> security expert either :)
>
> > In that case msg can be anything. On top of that, somebody may
> > mistakenly (inadvertently) put the code that allows user controller
> > input to go to this path.
>
> Yes. This is a good reason to not to do this - but I was interested in
> knowing if there is a potential risk even if:
>
> > > all the callers use this
> > > as
> > >
> > > die_loudly("foobarfoo\n");

I don't see direct issues, only indirect ones, for example, if by some
reason the memory of this message appears writable. So, whoever
controls the format string of printf() controls a lot. That's why it's
preferable to spell out exact intentions in the explicit format
string.

> > And last but not least, that some newbies might copy'n'paste bad
> > examples where they will expose security breach.
>
> Yes yes. As I said, I am not trying to say it is Ok. I was just
> wondering what are the risks if users of the print function were known.
>
> > With the modern world of Spectre, rowhammer, and other side channel
> > attacks I may believe that one may exhaust the regulator for getting
> > advantage on an attack vector.
> >
> > But again, not a security guy here.
>
> Thanks anyways :)

> > > > > +       BUG();
> > > > > +}

-- 
With Best Regards,
Andy Shevchenko