linux-kernel - Re: [PATCH v11 19/19] kasan: enable instrumentation of global variables

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Date:	Mon, 16 Feb 2015 13:28:09 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Andrey Ryabinin <a.ryabinin@...sung.com>,
	linux-kernel@...r.kernel.org
Cc:	Andrey Ryabinin <a.ryabinin@...sung.com>,
	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>,
	Andrew Morton <akpm@...ux-foundation.org>,
	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>, Michal Marek <mmarek@...e.cz>,
	"open list\:KERNEL BUILD + fi..." <linux-kbuild@...r.kernel.org>
Subject: Re: [PATCH v11 19/19] kasan: enable instrumentation of global variables

Andrey Ryabinin <a.ryabinin@...sung.com> writes:
> This feature let us to detect accesses out of bounds of
> global variables. This will work as for globals in kernel
> image, so for globals in modules. Currently this won't work
> for symbols in user-specified sections (e.g. __init, __read_mostly, ...)
>
> 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.

Hmm, I understand why you only fixed x86, but it's weird.

I think MODULE_ALIGN belongs in linux/moduleloader.h, and every arch
should be fixed up to use it (though you could leave that for later).

Might as well fix the default implementation at least.

> @@ -49,8 +49,15 @@ void kasan_krealloc(const void *object, size_t new_size);
>  void kasan_slab_alloc(struct kmem_cache *s, void *object);
>  void kasan_slab_free(struct kmem_cache *s, void *object);
>  
> +#define MODULE_ALIGN (PAGE_SIZE << KASAN_SHADOW_SCALE_SHIFT)
> +
> +int kasan_module_alloc(void *addr, size_t size);
> +void kasan_module_free(void *addr);
> +
>  #else /* CONFIG_KASAN */
>  
> +#define MODULE_ALIGN 1

Hmm, that should be PAGE_SIZE (we assume that in several places).

> @@ -1807,6 +1808,7 @@ static void unset_module_init_ro_nx(struct module *mod) { }
>  void __weak module_memfree(void *module_region)
>  {
>  	vfree(module_region);
> +	kasan_module_free(module_region);
>  }

This looks racy (memory reuse?).  Perhaps try other order?

Cheers,
Rusty.
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