Re: [PATCH v2 3/3] mm/usercopy: Detect compound page overruns

[Matthew Wilcox <willy@infradead.org>]

On Wed, Oct 06, 2021 at 01:42:26PM +0100, Matthew Wilcox (Oracle) wrote:
> Move the compound page overrun detection out of
> CONFIG_HARDENED_USERCOPY_PAGESPAN so it's enabled for more people.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Acked-by: Kees Cook <keescook@chromium.org>
> ---
>  mm/usercopy.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/usercopy.c b/mm/usercopy.c
> index 63476e1506e0..b825c4344917 100644
> --- a/mm/usercopy.c
> +++ b/mm/usercopy.c
> @@ -194,11 +194,6 @@ static inline void check_page_span(const void *ptr, unsigned long n,
>  		   ((unsigned long)end & (unsigned long)PAGE_MASK)))
>  		return;
>  
> -	/* Allow if fully inside the same compound (__GFP_COMP) page. */
> -	endpage = virt_to_head_page(end);
> -	if (likely(endpage == page))
> -		return;
> -
>  	/*
>  	 * Reject if range is entirely either Reserved (i.e. special or
>  	 * device memory), or CMA. Otherwise, reject since the object spans

Needs an extra hunk to avoid a warning with that config:

@@ -163,7 +163,6 @@ static inline void check_page_span(const void *ptr, unsigned long n,
 {
 #ifdef CONFIG_HARDENED_USERCOPY_PAGESPAN
        const void *end = ptr + n - 1;
-       struct page *endpage;
        bool is_reserved, is_cma;

        /*

I'll wait a few days and send a v3.