linux-kernel - Re: [kernel-hardening] Re: [PATCH v3 4/5] bug: Provide toggle for BUG on data corruption

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Date:   Mon, 22 Aug 2016 15:32:06 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>
Cc:     Arnd Bergmann <arnd@...db.de>, Laura Abbott <labbott@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Daniel Micay <danielmicay@...il.com>,
        Joe Perches <joe@...ches.com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Syed Rameez Mustafa <rameezmustafa@...eaurora.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Josh Triplett <josh@...htriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Jan Kara <jack@...e.cz>, Thomas Gleixner <tglx@...utronix.de>,
        Josef Bacik <jbacik@...com>, Ingo Molnar <mingo@...nel.org>,
        Tejun Heo <tj@...nel.org>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Nikolay Aleksandrov <nikolay@...ulusnetworks.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [kernel-hardening] Re: [PATCH v3 4/5] bug: Provide toggle for BUG
 on data corruption

On Mon, Aug 22, 2016 at 10:53 AM, Paul E. McKenney
<paulmck@...ux.vnet.ibm.com> wrote:
> On Mon, Aug 22, 2016 at 03:15:35PM +0200, Arnd Bergmann wrote:
>> On Wednesday, August 17, 2016 2:42:11 PM CEST Kees Cook wrote:
>> > +
>> > +/*
>> > + * Since detected data corruption should stop operation on the affected
>> > + * structures, this returns false if the corruption condition is found.
>> > + */
>> > +#define CHECK_DATA_CORRUPTION(condition, fmt, ...)                      \
>> > +       do {                                                             \
>> > +               if (unlikely(condition)) {                               \
>> > +                       if (IS_ENABLED(CONFIG_BUG_ON_DATA_CORRUPTION)) { \
>> > +                               pr_err(fmt, ##__VA_ARGS__);              \
>> > +                               BUG();                                   \
>> > +                       } else                                           \
>> > +                               WARN(1, fmt, ##__VA_ARGS__);             \
>> > +                       return false;                                    \
>> > +               }                                                        \
>> > +       } while (0)
>> > +
>>
>> I think the "return false" inside of the macro makes it easy to misread
>> what is actually going on.
>>
>> How about making it a macro that returns the condition argument?
>>
>> #define CHECK_DATA_CORRUPTION(condition, fmt, ...)    \
>> ({    \
>>       bool _condition = unlikely(condition);  \
>>       if (_condition) {       \
>>               ...
>>       }       \
>>       _condition;     \
>> })
>
> That does look better, now that you mention it.  Kees, any objections?

That's fine with me; it'll require changing the callers of the macros
to test their results, but that should be clean change.

-Kees

-- 
Kees Cook
Nexus Security