linux-kernel - Re: [PATCH v4] memory_hotplug: Add a bounds check to __add

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Message-ID: <20190926075307.GB17200@linux>
Date:   Thu, 26 Sep 2019 09:53:07 +0200
From:   Oscar Salvador <osalvador@...e.de>
To:     Alastair D'Silva <alastair@....ibm.com>
Cc:     alastair@...ilva.org, Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        David Hildenbrand <david@...hat.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Dan Williams <dan.j.williams@...el.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] memory_hotplug: Add a bounds check to __add_pages

On Thu, Sep 26, 2019 at 11:34:05AM +1000, Alastair D'Silva wrote:
> From: Alastair D'Silva <alastair@...ilva.org>
> 
> On PowerPC, the address ranges allocated to OpenCAPI LPC memory
> are allocated from firmware. These address ranges may be higher
> than what older kernels permit, as we increased the maximum
> permissable address in commit 4ffe713b7587
> ("powerpc/mm: Increase the max addressable memory to 2PB"). It is
> possible that the addressable range may change again in the
> future.
> 
> In this scenario, we end up with a bogus section returned from
> __section_nr (see the discussion on the thread "mm: Trigger bug on
> if a section is not found in __section_nr").
> 
> Adding a check here means that we fail early and have an
> opportunity to handle the error gracefully, rather than rumbling
> on and potentially accessing an incorrect section.
> 
> Further discussion is also on the thread ("powerpc: Perform a bounds
> check in arch_add_memory")
> http://lkml.kernel.org/r/20190827052047.31547-1-alastair@au1.ibm.com
> 
> Signed-off-by: Alastair D'Silva <alastair@...ilva.org>

Reviewed-by: Oscar Salvador <osalvador@...e.de>

Just a nit-picking below:

> ---
>  mm/memory_hotplug.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index c73f09913165..212804c0f7f5 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -278,6 +278,22 @@ static int check_pfn_span(unsigned long pfn, unsigned long nr_pages,
>  	return 0;
>  }
>  
> +static int check_hotplug_memory_addressable(unsigned long pfn,
> +					    unsigned long nr_pages)
> +{
> +	unsigned long max_addr = ((pfn + nr_pages) << PAGE_SHIFT) - 1;

I would use PFN_PHYS instead:

	unsigned long max_addr = PFN_PHYS(pfn + nr_pages) - 1;

> +
> +	if (max_addr >> MAX_PHYSMEM_BITS) {
> +		WARN(1,
> +		     "Hotplugged memory exceeds maximum addressable address, range=%#lx-%#lx, maximum=%#lx\n",
> +		     pfn << PAGE_SHIFT, max_addr,

Same here.

> +		     (1ul << (MAX_PHYSMEM_BITS + 1)) - 1);

I would use a local variable to hold this computation.

> +		return -E2BIG;
> +	}
> +
> +	return 0;

-- 
Oscar Salvador
SUSE L3