Re: [PATCH v7 1/1] memory_hotplug: Add a bounds check to __add_pages

Michal Hocko
2019-10-04T12:08:53Z

On Tue 01-10-19 10:46:15, Alastair D'Silva wrote:
> From: Alastair D'Silva <alastair@d-silva.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@d-silva.org>

I am sorry to come late to the party. This looks better.
Acked-by: Michal Hocko <mhocko@suse.com>

Thanks!
> ---
> mm/memory_hotplug.c | 20 ++++++++++++++++++++
> 1 file changed, 20 insertions(+)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index c73f09913165..5af9f4466ad1 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)
> +{
> + const u64 max_addr = PFN_PHYS(pfn + nr_pages) - 1;
> +
> + if (max_addr >> MAX_PHYSMEM_BITS) {
> + const u64 max_allowed = (1ull << (MAX_PHYSMEM_BITS + 1)) - 1;
> + WARN(1,
> + "Hotplugged memory exceeds maximum addressable address, range=%#llx-%#llx, maximum=%#llx\n",
> + (u64)PFN_PHYS(pfn), max_addr, max_allowed);
> + return -E2BIG;
> + }
> +
> + return 0;
> +}
> +
> /*
> * Reasonably generic function for adding memory. It is
> * expected that archs that support memory hotplug will
> @@ -291,6 +307,10 @@ int __ref __add_pages(int nid, unsigned long pfn, unsigned long nr_pages,
> unsigned long nr, start_sec, end_sec;
> struct vmem_altmap *altmap = restrictions->altmap;
>
> + err = check_hotplug_memory_addressable(pfn, nr_pages);
> + if (err)
> + return err;
> +
> if (altmap) {
> /*
> * Validate altmap is within bounds of the total request
> --
> 2.21.0

--
Michal Hocko
SUSE Labs