linux-kernel - Re: [PATCH resend RFC 2/9] s390/gmap: don't unconditionally call pte_unmap_unlock() in __gmap

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Message-ID: <20210914185232.3b86c7d3@p-imbrenda>
Date:   Tue, 14 Sep 2021 18:52:32 +0200
From:   Claudio Imbrenda <imbrenda@...ux.ibm.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org, linux-mm@...ck.org,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Niklas Schnelle <schnelle@...ux.ibm.com>,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        Ulrich Weigand <Ulrich.Weigand@...ibm.com>
Subject: Re: [PATCH resend RFC 2/9] s390/gmap: don't unconditionally call
 pte_unmap_unlock() in __gmap_zap()

On Thu,  9 Sep 2021 18:22:41 +0200
David Hildenbrand <david@...hat.com> wrote:

> ... otherwise we will try unlocking a spinlock that was never locked via a
> garbage pointer.
> 
> At the time we reach this code path, we usually successfully looked up
> a PGSTE already; however, evil user space could have manipulated the VMA
> layout in the meantime and triggered removal of the page table.
> 
> Fixes: 1e133ab296f3 ("s390/mm: split arch/s390/mm/pgtable.c")
> Signed-off-by: David Hildenbrand <david@...hat.com>

Reviewed-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>

> ---
>  arch/s390/mm/gmap.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
> index b6b56cd4ca64..9023bf3ced89 100644
> --- a/arch/s390/mm/gmap.c
> +++ b/arch/s390/mm/gmap.c
> @@ -690,9 +690,10 @@ void __gmap_zap(struct gmap *gmap, unsigned long gaddr)
>  
>  		/* Get pointer to the page table entry */
>  		ptep = get_locked_pte(gmap->mm, vmaddr, &ptl);
> -		if (likely(ptep))
> +		if (likely(ptep)) {
>  			ptep_zap_unused(gmap->mm, vmaddr, ptep, 0);
> -		pte_unmap_unlock(ptep, ptl);
> +			pte_unmap_unlock(ptep, ptl);
> +		}
>  	}
>  }
>  EXPORT_SYMBOL_GPL(__gmap_zap);