Re: [PATCH 3/5] mm: kfence: Pass a pointer to virt_to_page()

[Marco Elver <elver@google.com>]

On Thu, 30 Jun 2022 at 10:43, Linus Walleij <linus.walleij@linaro.org> wrote:
>
> Functions that work on a pointer to virtual memory such as
> virt_to_pfn() and users of that function such as
> virt_to_page() are supposed to pass a pointer to virtual
> memory, ideally a (void *) or other pointer. However since
> many architectures implement virt_to_pfn() as a macro,
> this function becomes polymorphic and accepts both a
> (unsigned long) and a (void *).
>
> If we instead implement a proper virt_to_pfn(void *addr)
> function the following happens (occurred on arch/arm):
>
> mm/kfence/core.c:558:30: warning: passing argument 1
>   of 'virt_to_pfn' makes pointer from integer without a
>   cast [-Wint-conversion]
>
> In one case we can refer to __kfence_pool directly (and
> that is a proper (char *) pointer) and in the other call
> site we use an explicit cast.
>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Alexander Potapenko <glider@google.com>
> Cc: Marco Elver <elver@google.com>
> Cc: Dmitry Vyukov <dvyukov@google.com>
> Cc: kasan-dev@googlegroups.com
> Cc: linux-mm@kvack.org
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Reviewed-by: Marco Elver <elver@google.com>

> ---
>  mm/kfence/core.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/kfence/core.c b/mm/kfence/core.c
> index 4e7cd4c8e687..153cde62ad72 100644
> --- a/mm/kfence/core.c
> +++ b/mm/kfence/core.c
> @@ -543,7 +543,7 @@ static unsigned long kfence_init_pool(void)
>         if (!arch_kfence_init_pool())
>                 return addr;
>
> -       pages = virt_to_page(addr);
> +       pages = virt_to_page(__kfence_pool);
>
>         /*
>          * Set up object pages: they must have PG_slab set, to avoid freeing
> @@ -657,7 +657,7 @@ static bool kfence_init_pool_late(void)
>         /* Same as above. */
>         free_size = KFENCE_POOL_SIZE - (addr - (unsigned long)__kfence_pool);
>  #ifdef CONFIG_CONTIG_ALLOC
> -       free_contig_range(page_to_pfn(virt_to_page(addr)), free_size / PAGE_SIZE);
> +       free_contig_range(page_to_pfn(virt_to_page((void *)addr)), free_size / PAGE_SIZE);
>  #else
>         free_pages_exact((void *)addr, free_size);
>  #endif
> --
> 2.36.1
>