linux-kernel - Re: [PATCH v6 01/10] mm/memunmap: Don't access uninitialized memmap in memunmap

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Message-ID: <c528655a-7050-506b-c9bb-632dfde6c209@redhat.com>
Date:   Mon, 14 Oct 2019 11:05:54 +0200
From:   David Hildenbrand <david@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, linux-arm-kernel@...ts.infradead.org,
        linux-ia64@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
        x86@...nel.org, "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Logan Gunthorpe <logang@...tatee.com>,
        Ira Weiny <ira.weiny@...el.com>
Subject: Re: [PATCH v6 01/10] mm/memunmap: Don't access uninitialized memmap
 in memunmap_pages()

On 06.10.19 10:56, David Hildenbrand wrote:
> From: "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
> 
> With an altmap, the memmap falling into the reserved altmap space are
> not initialized and, therefore, contain a garbage NID and a garbage
> zone. Make sure to read the NID/zone from a memmap that was initialzed.
> 
> This fixes a kernel crash that is observed when destroying a namespace:
> 
> [   81.356173] kernel BUG at include/linux/mm.h:1107!
> cpu 0x1: Vector: 700 (Program Check) at [c000000274087890]
>      pc: c0000000004b9728: memunmap_pages+0x238/0x340
>      lr: c0000000004b9724: memunmap_pages+0x234/0x340
> ...
>      pid   = 3669, comm = ndctl
> kernel BUG at include/linux/mm.h:1107!
> [c000000274087ba0] c0000000009e3500 devm_action_release+0x30/0x50
> [c000000274087bc0] c0000000009e4758 release_nodes+0x268/0x2d0
> [c000000274087c30] c0000000009dd144 device_release_driver_internal+0x174/0x240
> [c000000274087c70] c0000000009d9dfc unbind_store+0x13c/0x190
> [c000000274087cb0] c0000000009d8a24 drv_attr_store+0x44/0x60
> [c000000274087cd0] c0000000005a7470 sysfs_kf_write+0x70/0xa0
> [c000000274087d10] c0000000005a5cac kernfs_fop_write+0x1ac/0x290
> [c000000274087d60] c0000000004be45c __vfs_write+0x3c/0x70
> [c000000274087d80] c0000000004c26e4 vfs_write+0xe4/0x200
> [c000000274087dd0] c0000000004c2a6c ksys_write+0x7c/0x140
> [c000000274087e20] c00000000000bbd0 system_call+0x5c/0x68
> 
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Jason Gunthorpe <jgg@...pe.ca>
> Cc: Logan Gunthorpe <logang@...tatee.com>
> Cc: Ira Weiny <ira.weiny@...el.com>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
> [ minimze code changes, rephrase description ]
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---
>   mm/memremap.c | 11 +++++++----
>   1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/memremap.c b/mm/memremap.c
> index 557e53c6fb46..8c2fb44c3b4d 100644
> --- a/mm/memremap.c
> +++ b/mm/memremap.c
> @@ -123,6 +123,7 @@ static void dev_pagemap_cleanup(struct dev_pagemap *pgmap)
>   void memunmap_pages(struct dev_pagemap *pgmap)
>   {
>   	struct resource *res = &pgmap->res;
> +	struct page *first_page;
>   	unsigned long pfn;
>   	int nid;
>   
> @@ -131,14 +132,16 @@ void memunmap_pages(struct dev_pagemap *pgmap)
>   		put_page(pfn_to_page(pfn));
>   	dev_pagemap_cleanup(pgmap);
>   
> +	/* make sure to access a memmap that was actually initialized */
> +	first_page = pfn_to_page(pfn_first(pgmap));
> +
>   	/* pages are dead and unused, undo the arch mapping */
> -	nid = page_to_nid(pfn_to_page(PHYS_PFN(res->start)));
> +	nid = page_to_nid(first_page);
>   
>   	mem_hotplug_begin();
>   	if (pgmap->type == MEMORY_DEVICE_PRIVATE) {
> -		pfn = PHYS_PFN(res->start);
> -		__remove_pages(page_zone(pfn_to_page(pfn)), pfn,
> -				 PHYS_PFN(resource_size(res)), NULL);
> +		__remove_pages(page_zone(first_page), PHYS_PFN(res->start),
> +			       PHYS_PFN(resource_size(res)), NULL);
>   	} else {
>   		arch_remove_memory(nid, res->start, resource_size(res),
>   				pgmap_altmap(pgmap));
> 

@Andrew, can you add

Fixes: 2c2a5af6fed2 ("mm, memory_hotplug: add nid parameter to 
arch_remove_memory")

(which basically introduced the nid = page_to_nid(first_page))

The "page_zone(pfn_to_page(pfn)" was introduced by 69324b8f4833 ("mm, 
devm_memremap_pages: add MEMORY_DEVICE_PRIVATE support"), however, I 
think we will never have driver reserved memory with 
MEMORY_DEVICE_PRIVATE (no altmap AFAIKS).

Also, I think

Cc: stable@...r.kernel.org # v5.0+

makes sense.

-- 

Thanks,

David / dhildenb