On Wed, 26 Jun 2019 16:20:13 +0200 Marco Elver <elver@xxxxxxxxxx> wrote:
> This refactors common code of ksize() between the various allocators
> into slab_common.c: __ksize() is the allocator-specific implementation
> without instrumentation, whereas ksize() includes the required KASAN
> logic.
>
> ...
>
> /**
> - * ksize - get the actual amount of memory allocated for a given object
> - * @objp: Pointer to the object
> + * __ksize -- Uninstrumented ksize.
> *
> - * kmalloc may internally round up allocations and return more memory
> - * than requested. ksize() can be used to determine the actual amount of
> - * memory allocated. The caller may use this additional memory, even though
> - * a smaller amount of memory was initially specified with the kmalloc call.
> - * The caller must guarantee that objp points to a valid object previously
> - * allocated with either kmalloc() or kmem_cache_alloc(). The object
> - * must not be freed during the duration of the call.
> - *
> - * Return: size of the actual memory used by @objp in bytes
> + * Unlike ksize(), __ksize() is uninstrumented, and does not provide the same
> + * safety checks as ksize() with KASAN instrumentation enabled.
> */
> -size_t ksize(const void *objp)
> +size_t __ksize(const void *objp)
> {
> - size_t size;
> -
> BUG_ON(!objp);
> if (unlikely(objp == ZERO_SIZE_PTR))
> return 0;
>
> - size = virt_to_cache(objp)->object_size;
> - /* We assume that ksize callers could use the whole allocated area,
> - * so we need to unpoison this area.
> - */
> - kasan_unpoison_shadow(objp, size);
> -
> - return size;
> + return virt_to_cache(objp)->object_size;
> }
This conflicts with Kees's "mm/slab: sanity-check page type when
looking up cache".
https://ozlabs.org/~akpm/mmots/broken-out/mm-slab-sanity-check-page-type-when-looking-up-cache.patch
Here's what I ended up with:
/**
* __ksize -- Uninstrumented ksize.
*
* Unlike ksize(), __ksize() is uninstrumented, and does not provide the same
* safety checks as ksize() with KASAN instrumentation enabled.
*/
size_t __ksize(const void *objp)
{
size_t size;
struct kmem_cache *c;
BUG_ON(!objp);
if (unlikely(objp == ZERO_SIZE_PTR))
return 0;
c = virt_to_cache(objp);
size = c ? c->object_size : 0;
return size;
}
EXPORT_SYMBOL(__ksize);
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -1597,6 +1597,32 @@ void kzfree(const void *p)
> }
> EXPORT_SYMBOL(kzfree);
>
> +/**
> + * ksize - get the actual amount of memory allocated for a given object
> + * @objp: Pointer to the object
> + *
> + * kmalloc may internally round up allocations and return more memory
> + * than requested. ksize() can be used to determine the actual amount of
> + * memory allocated. The caller may use this additional memory, even though
> + * a smaller amount of memory was initially specified with the kmalloc call.
> + * The caller must guarantee that objp points to a valid object previously
> + * allocated with either kmalloc() or kmem_cache_alloc(). The object
> + * must not be freed during the duration of the call.
> + *
> + * Return: size of the actual memory used by @objp in bytes
> + */
> +size_t ksize(const void *objp)
> +{
> + size_t size = __ksize(objp);
> + /*
> + * We assume that ksize callers could use whole allocated area,
> + * so we need to unpoison this area.
> + */
> + kasan_unpoison_shadow(objp, size);
> + return size;
> +}
> +EXPORT_SYMBOL(ksize);
That looks OK still.
