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

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Date:   Mon, 22 Aug 2016 15:15:35 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Kees Cook <keescook@...omium.org>
Cc:     "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        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>,
        linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH v3 4/5] bug: Provide toggle for BUG on data corruption

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;	\
})

	Arnd