linux-hardening - Re: [PATCH 2/3] usercopy: Cast pointer to an integer once

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Date:   Mon, 13 Jun 2022 09:20:36 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Uladzislau Rezki <urezki@...il.com>
Cc:     "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        linux-mm@...ck.org, Zorro Lang <zlang@...hat.com>,
        linux-xfs@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH 2/3] usercopy: Cast pointer to an integer once

On Mon, Jun 13, 2022 at 11:51:24AM +0200, Uladzislau Rezki wrote:
> On Sun, Jun 12, 2022 at 10:32:26PM +0100, Matthew Wilcox (Oracle) wrote:
> > Get rid of a lot of annoying casts by setting 'addr' once at the top
> > of the function.
> > 
> > Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> > ---
> >  mm/usercopy.c | 11 ++++++-----
> >  1 file changed, 6 insertions(+), 5 deletions(-)
> > 
> > diff --git a/mm/usercopy.c b/mm/usercopy.c
> > index fdd1bed3b90a..31deee7dd2f5 100644
> > --- a/mm/usercopy.c
> > +++ b/mm/usercopy.c
> > @@ -161,19 +161,20 @@ static inline void check_bogus_address(const unsigned long ptr, unsigned long n,
> >  static inline void check_heap_object(const void *ptr, unsigned long n,
> >  				     bool to_user)
> >  {
> > +	uintptr_t addr = (uintptr_t)ptr;
> >  	struct folio *folio;
> >  
> >  	if (is_kmap_addr(ptr)) {
> > -		unsigned long page_end = (unsigned long)ptr | (PAGE_SIZE - 1);
> > +		unsigned long page_end = addr | (PAGE_SIZE - 1);
> >  
> > -		if ((unsigned long)ptr + n - 1 > page_end)
> > +		if (addr + n - 1 > page_end)
> >  			usercopy_abort("kmap", NULL, to_user,
> >  					offset_in_page(ptr), n);
> >  		return;
> >  	}
> >  
> >  	if (is_vmalloc_addr(ptr)) {
> > -		struct vmap_area *area = find_vmap_area((unsigned long)ptr);
> > +		struct vmap_area *area = find_vmap_area(addr);
> >  		unsigned long offset;
> >  
> >  		if (!area) {
> > @@ -183,8 +184,8 @@ static inline void check_heap_object(const void *ptr, unsigned long n,
> >  
> >  		/* XXX: We should also abort for free vmap_areas */
> >  
> > -		offset = (unsigned long)ptr - area->va_start;
> > -		if ((unsigned long)ptr + n > area->va_end)
> > +		offset = addr - area->va_start;
> > +		if (addr + n > area->va_end)
> >  			usercopy_abort("vmalloc", NULL, to_user, offset, n);
> >  		return;
> >  	}
> > -- 
> > 2.35.1
> > 
> Looks good to me: Reviewed-by: Uladzislau Rezki (Sony) <urezki@...il.com>

For the future, please put your tags ("Reviewed-by") on a separate line
or the workflow tools (b4, patchwork, etc) won't see it. :)

-- 
Kees Cook