linux-kernel - Re: [PATCH v2 4/5] bug: Provide toggle for BUG on data corruption

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Message-ID: <CAGXu5jKvNGG+SmHe7zGS7F=2K7RShSV6+U6Yot4zHoPZz4aqdA@mail.gmail.com>
Date:	Tue, 16 Aug 2016 20:39:07 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Joe Perches <joe@...ches.com>
Cc:	"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
	Laura Abbott <labbott@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Daniel Micay <danielmicay@...il.com>,
	Arnd Bergmann <arnd@...db.de>,
	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>,
	Dan Williams <dan.j.williams@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Josef Bacik <jbacik@...com>,
	Andrey Ryabinin <aryabinin@...tuozzo.com>,
	Tejun Heo <tj@...nel.org>,
	Nikolay Aleksandrov <nikolay@...ulusnetworks.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v2 4/5] bug: Provide toggle for BUG on data corruption

On Tue, Aug 16, 2016 at 5:26 PM, Joe Perches <joe@...ches.com> wrote:
> On Tue, 2016-08-16 at 17:20 -0700, Kees Cook wrote:
>> The kernel checks for cases of data structure corruption under some
>> CONFIGs (e.g. CONFIG_DEBUG_LIST). When corruption is detected, some
>> systems may want to BUG() immediately instead of letting the system run
>> with known corruption.  Usually these kinds of manipulation primitives can
>> be used by security flaws to gain arbitrary memory write control. This
>> provides a new config CONFIG_BUG_ON_DATA_CORRUPTION and a corresponding
>> macro CHECK_DATA_CORRUPTION for handling these situations. Notably, even
>> if not BUGing, the kernel should not continue processing the corrupted
>> structure.
> []
>> diff --git a/include/linux/bug.h b/include/linux/bug.h
> []
>> @@ -118,4 +118,21 @@ static inline enum bug_trap_type report_bug(unsigned long bug_addr,
>>  }
>>
>>  #endif       /* CONFIG_GENERIC_BUG */
>> +
>> +/*
>> + * 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, format...)                   \
>
> My preference would be to use (condition, fmt, ...)
>
>> +     do {                                                             \
>> +             if (unlikely(condition)) {                               \
>> +                     if (IS_ENABLED(CONFIG_BUG_ON_DATA_CORRUPTION)) { \
>> +                             printk(KERN_ERR format);                 \
>
> and
>                                 pr_err(fmt, ##__VA_ARGS__);
>
> so that any use would also get any local pr_fmt applied as well.
>
>> +                             BUG();                                   \
>> +                     } else                                           \
>> +                             WARN(1, format);                         \
>> +                     return false;                                    \
>> +             }                                                        \
>> +     } while (0)
>> +
>>  #endif       /* _LINUX_BUG_H */
>

Ah yes, excellent point. I'll convert this for my v3. Thanks!

-Kees

-- 
Kees Cook
Nexus Security