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

From: Rusty Russell
Date: Sun Feb 15 2015 - 23:11:29 EST

Andrey Ryabinin <a.ryabinin@xxxxxxxxxxx> 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);
> +
> +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?

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