linux-kernel - Re: [PATCH v10 17/17] kasan: enable instrumentation of global variables

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Date:	Thu, 29 Jan 2015 15:13:32 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Andrey Ryabinin <a.ryabinin@...sung.com>
Cc:	linux-kernel@...r.kernel.org, Dmitry Vyukov <dvyukov@...gle.com>,
	Konstantin Serebryany <kcc@...gle.com>,
	Dmitry Chernenkov <dmitryc@...gle.com>,
	Andrey Konovalov <adech.fo@...il.com>,
	Yuri Gribov <tetra2005@...il.com>,
	Konstantin Khlebnikov <koct9i@...il.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Christoph Lameter <cl@...ux.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Dave Hansen <dave.hansen@...el.com>,
	Andi Kleen <andi@...stfloor.org>, x86@...nel.org,
	linux-mm@...ck.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Michal Marek <mmarek@...e.cz>,
	linux-kbuild@...r.kernel.org (open list:KERNEL BUILD + fi...)
Subject: Re: [PATCH v10 17/17] kasan: enable instrumentation of global
 variables

On Thu, 29 Jan 2015 18:12:01 +0300 Andrey Ryabinin <a.ryabinin@...sung.com> wrote:

> This feature let us to detect accesses out of bounds
> of global variables.

global variables *within modules*, I think?  More specificity needed here.

> The idea of this is simple. Compiler increases each global variable
> by redzone size and add constructors invoking __asan_register_globals()
> function. Information about global variable (address, size,
> size with redzone ...) passed to __asan_register_globals() so we could
> poison variable's redzone.
> 
> This patch also forces module_alloc() to return 8*PAGE_SIZE aligned
> address making shadow memory handling ( kasan_module_alloc()/kasan_module_free() )
> more simple. Such alignment guarantees that each shadow page backing
> modules address space correspond to only one module_alloc() allocation.
> 
> ...
>
> +int kasan_module_alloc(void *addr, size_t size)
> +{
> +
> +	size_t shadow_size = round_up(size >> KASAN_SHADOW_SCALE_SHIFT,
> +				PAGE_SIZE);
> +	unsigned long shadow_start = kasan_mem_to_shadow((unsigned long)addr);
> +	void *ret;

Like this:

	size_t shadow_size;
	unsigned long shadow_start;
	void *ret;

	shadow_size = round_up(size >> KASAN_SHADOW_SCALE_SHIFT, PAGE_SIZE);
	shadow_start = kasan_mem_to_shadow((unsigned long)addr);

it's much easier to read and avoids the 80-column trickery.

I do suspect that

	void *kasan_mem_to_shadow(const void *addr);

would clean up lots and lots of code.

> +	if (WARN_ON(!PAGE_ALIGNED(shadow_start)))
> +		return -EINVAL;
> +
> +	ret = __vmalloc_node_range(shadow_size, 1, shadow_start,
> +			shadow_start + shadow_size,
> +			GFP_KERNEL | __GFP_HIGHMEM | __GFP_ZERO,
> +			PAGE_KERNEL, VM_NO_GUARD, NUMA_NO_NODE,
> +			__builtin_return_address(0));
> +	return ret ? 0 : -ENOMEM;
> +}
> +
> 
> ...
>
> +struct kasan_global {
> +	const void *beg;		/* Address of the beginning of the global variable. */
> +	size_t size;			/* Size of the global variable. */
> +	size_t size_with_redzone;	/* Size of the variable + size of the red zone. 32 bytes aligned */
> +	const void *name;
> +	const void *module_name;	/* Name of the module where the global variable is declared. */
> +	unsigned long has_dynamic_init;	/* This needed for C++ */

This can be removed?

> +#if KASAN_ABI_VERSION >= 4
> +	struct kasan_source_location *location;
> +#endif
> +};
> 
> ...
>

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