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

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Date:	Tue, 16 Aug 2016 17:26:09 -0700
From:	Joe Perches <joe@...ches.com>
To:	Kees Cook <keescook@...omium.org>,
	"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	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>,
	linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH v2 4/5] bug: Provide toggle for BUG on data corruption

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 */