Subject: Re: [PATCH v6 01/10] mm/memunmap: Don't access uninitialized memmap in memunmap_pages()

From: Damian Tometzki <[email-masked]>
Date: Sun, 6 Oct 2019 21:58:39 +0200

Hello David,

patch 05/10 is missing in the patch series. 

On Sun, 06. Oct 10:56, David Hildenbrand wrote:
> From: "Aneesh Kumar K.V" <[email-masked]>
> 
> 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 <[email-masked]>
> Cc: Andrew Morton <[email-masked]>
> Cc: Jason Gunthorpe <[email-masked]>
> Cc: Logan Gunthorpe <[email-masked]>
> Cc: Ira Weiny <[email-masked]>
> Signed-off-by: Aneesh Kumar K.V <[email-masked]>
> [ minimze code changes, rephrase description ]
> Signed-off-by: David Hildenbrand <[email-masked]>
> ---
>  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);

Why we need 'nid = page_to_nid(first_page)' we didnt use it anymore in this function ?

>  
>  	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));
> -- 
> 2.21.0
>
Best regards
Damian

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