linux-kernel - Re: [PATCH] mm: Prevent mapping slab pages to userspace

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Message-ID: <87bm3xpsqx.fsf@concordia.ellerman.id.au>
Date:   Thu, 31 Jan 2019 11:37:10 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Matthew Wilcox <willy@...radead.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Rik van Riel <riel@...riel.com>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        kernel-hardening@...ts.openwall.com,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH] mm: Prevent mapping slab pages to userspace

Matthew Wilcox <willy@...radead.org> writes:

> It's never appropriate to map a page allocated by SLAB into userspace.
> A buggy device driver might try this, or an attacker might be able to
> find a way to make it happen.
>
> Signed-off-by: Matthew Wilcox <willy@...radead.org>
> ---
>  mm/memory.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index e11ca9dd823f..ce8c90b752be 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1451,7 +1451,7 @@ static int insert_page(struct vm_area_struct *vma, unsigned long addr,
>  	spinlock_t *ptl;
>  
>  	retval = -EINVAL;
> -	if (PageAnon(page))
> +	if (PageAnon(page) || PageSlab(page))
>  		goto out;
>  	retval = -ENOMEM;
>  	flush_dcache_page(page);


Thanks for turning this into an actual patch.

cheers