linux-kernel - Re: [PATCH RFC 5/9] s390/uv: fully validate the VMA before calling follow

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Date:   Fri, 10 Sep 2021 14:14:12 +0000
From:   Liam Howlett <liam.howlett@...cle.com>
To:     David Hildenbrand <david@...hat.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH RFC 5/9] s390/uv: fully validate the VMA before calling
 follow_page()

* David Hildenbrand <david@...hat.com> [210909 11:01]:
> We should not walk/touch page tables outside of VMA boundaries when
> holding only the mmap sem in read mode. Evil user space can modify the
> VMA layout just before this function runs and e.g., trigger races with
> page table removal code since commit dd2283f2605e ("mm: mmap: zap pages
> with read mmap_sem in munmap").
> 
> find_vma() does not check if the address is >= the VMA start address;
> use vma_lookup() instead.
> 
> Fixes: 214d9bbcd3a6 ("s390/mm: provide memory management functions for protected KVM guests")
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---
>  arch/s390/kernel/uv.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c
> index aeb0a15bcbb7..193205fb2777 100644
> --- a/arch/s390/kernel/uv.c
> +++ b/arch/s390/kernel/uv.c
> @@ -227,7 +227,7 @@ int gmap_make_secure(struct gmap *gmap, unsigned long gaddr, void *uvcb)
>  	uaddr = __gmap_translate(gmap, gaddr);
>  	if (IS_ERR_VALUE(uaddr))
>  		goto out;
> -	vma = find_vma(gmap->mm, uaddr);
> +	vma = vma_lookup(gmap->mm, uaddr);
>  	if (!vma)
>  		goto out;
>  	/*
> -- 
> 2.31.1
> 
> 

Reviewed-by: Liam R. Howlett <Liam.Howlett@...cle.com>