RE: [PATCH 1/2] memory_hotplug: Add a bounds check to check_hotplug_memory_range()

[Alastair D'Silva]

> -----Original Message-----
> From: David Hildenbrand <david@xxxxxxxxxx>
> Sent: Tuesday, 10 September 2019 5:46 PM
> To: Alastair D'Silva <alastair@xxxxxxxxxxx>; alastair@xxxxxxxxxxx
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>; Oscar Salvador
> <osalvador@xxxxxxxx>; Michal Hocko <mhocko@xxxxxxxx>; Pavel Tatashin
> <pasha.tatashin@xxxxxxxxxx>; Wei Yang <richard.weiyang@xxxxxxxxx>;
> Dan Williams <dan.j.williams@xxxxxxxxx>; Qian Cai <cai@xxxxxx>; Jason
> Gunthorpe <jgg@xxxxxxxx>; Logan Gunthorpe <logang@xxxxxxxxxxxx>; Ira
> Weiny <ira.weiny@xxxxxxxxx>; linux-mm@xxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH 1/2] memory_hotplug: Add a bounds check to
> check_hotplug_memory_range()
> 
> On 10.09.19 04:52, Alastair D'Silva wrote:
> > From: Alastair D'Silva <alastair@xxxxxxxxxxx>
> >
> > 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").
> >
> > Signed-off-by: Alastair D'Silva <alastair@xxxxxxxxxxx>
> > ---
> >  include/linux/memory_hotplug.h |  1 +
> >  mm/memory_hotplug.c            | 19 ++++++++++++++++++-
> >  2 files changed, 19 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/linux/memory_hotplug.h
> > b/include/linux/memory_hotplug.h index f46ea71b4ffd..bc477e98a310
> > 100644
> > --- a/include/linux/memory_hotplug.h
> > +++ b/include/linux/memory_hotplug.h
> > @@ -110,6 +110,7 @@ extern void
> > __online_page_increment_counters(struct page *page);  extern void
> > __online_page_free(struct page *page);
> >
> >  extern int try_online_node(int nid);
> > +int check_hotplug_memory_addressable(u64 start, u64 size);
> >
> >  extern int arch_add_memory(int nid, u64 start, u64 size,
> >  			struct mhp_restrictions *restrictions); diff --git
> > a/mm/memory_hotplug.c b/mm/memory_hotplug.c index
> > c73f09913165..3c5428b014f9 100644
> > --- a/mm/memory_hotplug.c
> > +++ b/mm/memory_hotplug.c
> > @@ -1030,6 +1030,23 @@ int try_online_node(int nid)
> >  	return ret;
> >  }
> >
> > +#ifndef MAX_POSSIBLE_PHYSMEM_BITS
> > +#ifdef MAX_PHYSMEM_BITS
> > +#define MAX_POSSIBLE_PHYSMEM_BITS MAX_PHYSMEM_BITS #endif
> #endif
> > +
> 
> I think using MAX_POSSIBLE_PHYSMEM_BITS bits is wrong. You should use
> MAX_PHYSMEM_BITS.
> 
> E.g. on x86_64, MAX_POSSIBLE_PHYSMEM_BITS is 52, while
> MAX_PHYSMEM_BITS is (pgtable_l5_enabled() ? 52 : 46) - so
> MAX_PHYSMEM_BITS depends on the actual HW.
> 

Thanks, I was following the pattern from zsmalloc.c, but what you say makes sense.

> > +int check_hotplug_memory_addressable(u64 start, u64 size) { #ifdef
> > +MAX_POSSIBLE_PHYSMEM_BITS
> > +	if ((start + size - 1) >> MAX_POSSIBLE_PHYSMEM_BITS)
> > +		return -E2BIG;
> > +#endif
> > +
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(check_hotplug_memory_addressable);
> > +
> >  static int check_hotplug_memory_range(u64 start, u64 size)  {
> >  	/* memory range must be block size aligned */ @@ -1040,7 +1057,7
> @@
> > static int check_hotplug_memory_range(u64 start, u64 size)
> >  		return -EINVAL;
> >  	}
> >
> > -	return 0;
> > +	return check_hotplug_memory_addressable(start, size);
> >  }
> >
> >  static int online_memory_block(struct memory_block *mem, void *arg)
> >
> 
> 
> --
> 
> Thanks,
> 
> David / dhildenb
> 


-- 
Alastair D'Silva           mob: 0423 762 819
skype: alastair_dsilva     msn: alastair@xxxxxxxxxxx
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