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

Kees Cook
2016-08-22T22:32:10Z

On Mon, Aug 22, 2016 at 10:53 AM, Paul E. McKenney
<paulmck@linux.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