linux-kernel - Re: [PATCH v1] drivers/base/memory.c: Don't access uninitialized memmaps in soft_offline_page

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Date:   Fri, 11 Oct 2019 06:13:35 +0000
From:   Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:     David Hildenbrand <david@...hat.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        "Michal Hocko" <mhocko@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v1] drivers/base/memory.c: Don't access uninitialized
 memmaps in soft_offline_page_store()

On Thu, Oct 10, 2019 at 04:12:00PM +0200, David Hildenbrand wrote:
> Uninitialized memmaps contain garbage and in the worst case trigger kernel
> BUGs, especially with CONFIG_PAGE_POISONING. They should not get
> touched.
> 
> Right now, when trying to soft-offline a PFN that resides on a memory
> block that was never onlined, one gets a misleading error with
> CONFIG_PAGE_POISONING:
>   :/# echo 5637144576 > /sys/devices/system/memory/soft_offline_page
>   [   23.097167] soft offline: 0x150000 page already poisoned
> 
> But the actual result depends on the garbage in the memmap.
> 
> soft_offline_page() can only work with online pages, it returns -EIO in
> case of ZONE_DEVICE. Make sure to only forward pages that are online
> (iow, managed by the buddy) and, therefore, have an initialized memmap.
> 
> Add a check against pfn_to_online_page() and similarly return -EIO.
> 
> Fixes: f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded memory to zones until online") # visible after d0dc12e86b319
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: "Rafael J. Wysocki" <rafael@...nel.org>
> Cc: Michal Hocko <mhocko@...nel.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---
>  drivers/base/memory.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index 6bea4f3f8040..55907c27075b 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -540,6 +540,9 @@ static ssize_t soft_offline_page_store(struct device *dev,
>  	pfn >>= PAGE_SHIFT;
>  	if (!pfn_valid(pfn))
>  		return -ENXIO;
> +	/* Only online pages can be soft-offlined (esp., not ZONE_DEVICE). */
> +	if (!pfn_to_online_page(pfn))
> +		return -EIO;

Acked-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>

I think this check could be placed in soft_offline_page(), but that requires
a few more unrelated lines of changes due to the mismatch on type of parameter
between memory_failure() and soft_offline_page(),  This is not your problem,
and I plan to do some cleanup on related interfaces, so this patch is fine.

- Naoya Horiguchi