Re: [PATCH v6 11/18] khwasan, mm: perform untagged pointers comparison in krealloc

[Christopher Lameter <cl@linux.com>]

Reviewed-by: Christoph Lameter <cl@linux.com>


On Wed, 29 Aug 2018, Andrey Konovalov wrote:

> The krealloc function checks where the same buffer was reused or a new one
> allocated by comparing kernel pointers. KHWASAN changes memory tag on the
> krealloc'ed chunk of memory and therefore also changes the pointer tag of
> the returned pointer. Therefore we need to perform comparison on untagged
> (with tags reset) pointers to check whether it's the same memory region or
> not.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> ---
>  mm/slab_common.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 3abfa0f86118..0d588dfebd7d 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -1513,7 +1513,7 @@ void *krealloc(const void *p, size_t new_size, gfp_t flags)
>  	}
>
>  	ret = __do_krealloc(p, new_size, flags);
> -	if (ret && p != ret)
> +	if (ret && khwasan_reset_tag(p) != khwasan_reset_tag(ret))
>  		kfree(p);
>
>  	return ret;
>