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

From Kees Cook <keescook@chromium.org>
Newsgroups linux.kernel
Subject Re: [kernel-hardening] Re: [PATCH v3 4/5] bug: Provide toggle for BUG on data corruption
Date 2016-08-23 00:40 +0200
Message-ID <s962R-3Tc-9@gated-at.bofh.it> (permalink)
References <s7gSJ-6Zu-3@gated-at.bofh.it> <s7gSK-6Zu-19@gated-at.bofh.it> <s8XiW-6LP-35@gated-at.bofh.it> <s91FU-WO-25@gated-at.bofh.it>
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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

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[PATCH v3 0/5] bug: Provide toggle for BUG on data corruption Kees Cook <keescook@chromium.org> - 2016-08-17 23:50 +0200
  [PATCH v3 4/5] bug: Provide toggle for BUG on data corruption Kees Cook <keescook@chromium.org> - 2016-08-17 23:50 +0200
    Re: [PATCH v3 4/5] bug: Provide toggle for BUG on data corruption Arnd Bergmann <arnd@arndb.de> - 2016-08-22 15:20 +0200
      Re: [PATCH v3 4/5] bug: Provide toggle for BUG on data corruption "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-08-22 20:00 +0200
        Re: [kernel-hardening] Re: [PATCH v3 4/5] bug: Provide toggle for BUG  on data corruption Kees Cook <keescook@chromium.org> - 2016-08-23 00:40 +0200
  Re: [PATCH v3 0/5] bug: Provide toggle for BUG on data corruption Steven Rostedt <rostedt@goodmis.org> - 2016-08-18 15:50 +0200
    Re: [PATCH v3 0/5] bug: Provide toggle for BUG on data corruption "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-08-19 03:10 +0200
  Re: [kernel-hardening] [PATCH v3 0/5] bug: Provide toggle for BUG  on data corruption Rik van Riel <riel@redhat.com> - 2016-08-19 03:00 +0200
    Re: [kernel-hardening] [PATCH v3 0/5] bug: Provide toggle for BUG on  data corruption "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-08-19 03:30 +0200
      Re: [kernel-hardening] [PATCH v3 0/5] bug: Provide toggle for BUG  on data corruption Rik van Riel <riel@redhat.com> - 2016-08-19 05:00 +0200
        Re: [kernel-hardening] [PATCH v3 0/5] bug: Provide toggle for BUG on  data corruption "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-08-19 19:50 +0200

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