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From: Vlastimil Babka <vbabka@suse.cz>
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	linux-api@vger.kernel.org, Michal Hocko <mhocko@kernel.org>,
	stable@vger.kernel.org
Subject: Re: [PATCH] mm/hugetlb: Fix NULL-pointer dereference on 5-level paging machine
Date: Wed, 22 Nov 2017 13:36:43 +0100	[thread overview]
Message-ID: <88a7a176-6070-2bf1-4579-d5fccdfc7f37@suse.cz> (raw)
In-Reply-To: <20171122121921.64822-1-kirill.shutemov@linux.intel.com>

On 11/22/2017 01:19 PM, Kirill A. Shutemov wrote:
> I've made mistake during converting hugetlb code to 5-level paging:
> in huge_pte_alloc() we have to use p4d_alloc(), not p4d_offset().
> Otherwise it leads to crash -- NULL-pointer dereference in pud_alloc()
> if p4d table is not yet allocated.
> 
> It only can happen in 5-level paging mode. In 4-level paging mode
> p4d_offset() always returns pgd, so we are fine.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Fixes: c2febafc6773 ("mm: convert generic code to 5-level paging")
> Cc: <stable@vger.kernel.org> # v4.11+

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
>  mm/hugetlb.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 2d2ff5e8bf2b..94a4c0b63580 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -4617,7 +4617,9 @@ pte_t *huge_pte_alloc(struct mm_struct *mm,
>  	pte_t *pte = NULL;
>  
>  	pgd = pgd_offset(mm, addr);
> -	p4d = p4d_offset(pgd, addr);
> +	p4d = p4d_alloc(mm, pgd, addr);
> +	if (!p4d)
> +		return NULL;
>  	pud = pud_alloc(mm, p4d, addr);
>  	if (pud) {
>  		if (sz == PUD_SIZE) {
> 

WARNING: multiple messages have this Message-ID (diff)
From: Vlastimil Babka <vbabka@suse.cz>
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	linux-api@vger.kernel.org, Michal Hocko <mhocko@kernel.org>,
	stable@vger.kernel.org
Subject: Re: [PATCH] mm/hugetlb: Fix NULL-pointer dereference on 5-level paging machine
Date: Wed, 22 Nov 2017 13:36:43 +0100	[thread overview]
Message-ID: <88a7a176-6070-2bf1-4579-d5fccdfc7f37@suse.cz> (raw)
In-Reply-To: <20171122121921.64822-1-kirill.shutemov@linux.intel.com>

On 11/22/2017 01:19 PM, Kirill A. Shutemov wrote:
> I've made mistake during converting hugetlb code to 5-level paging:
> in huge_pte_alloc() we have to use p4d_alloc(), not p4d_offset().
> Otherwise it leads to crash -- NULL-pointer dereference in pud_alloc()
> if p4d table is not yet allocated.
> 
> It only can happen in 5-level paging mode. In 4-level paging mode
> p4d_offset() always returns pgd, so we are fine.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Fixes: c2febafc6773 ("mm: convert generic code to 5-level paging")
> Cc: <stable@vger.kernel.org> # v4.11+

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
>  mm/hugetlb.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 2d2ff5e8bf2b..94a4c0b63580 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -4617,7 +4617,9 @@ pte_t *huge_pte_alloc(struct mm_struct *mm,
>  	pte_t *pte = NULL;
>  
>  	pgd = pgd_offset(mm, addr);
> -	p4d = p4d_offset(pgd, addr);
> +	p4d = p4d_alloc(mm, pgd, addr);
> +	if (!p4d)
> +		return NULL;
>  	pud = pud_alloc(mm, p4d, addr);
>  	if (pud) {
>  		if (sz == PUD_SIZE) {
> 

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  reply	other threads:[~2017-11-22 12:36 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-11-22 12:19 [PATCH] mm/hugetlb: Fix NULL-pointer dereference on 5-level paging machine Kirill A. Shutemov
2017-11-22 12:19 ` Kirill A. Shutemov
2017-11-22 12:36 ` Vlastimil Babka [this message]
2017-11-22 12:36   ` Vlastimil Babka
2017-11-22 12:47 ` Michal Hocko
2017-11-22 12:47   ` Michal Hocko

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