Re: [RESENT PATCH] x86/mem: fix the offset overflow when read/write mem

From: zhong jiang
Date: Wed May 03 2017 - 22:30:02 EST

On 2017/5/4 2:46, Rik van Riel wrote:
> On Tue, 2017-05-02 at 13:54 -0700, David Rientjes wrote:
>>> diff --git a/drivers/char/mem.c b/drivers/char/mem.c
>>> index 7e4a9d1..3a765e02 100644
>>> --- a/drivers/char/mem.c
>>> +++ b/drivers/char/mem.c
>>> @@ -55,7 +55,7 @@ static inline int
>> valid_phys_addr_range(phys_addr_t addr, size_t count)
>>> static inline int valid_mmap_phys_addr_range(unsigned long pfn,
>> size_t size)
>>> {
>>> - return 1;
>>> + return (pfn << PAGE_SHIFT) + size <= __pa(high_memory);
>>> }
>>> #endif
>> I suppose you are correct that there should be some sanity checking
>> on the
>> size used for the mmap().
> My apologies for not responding earlier. It may
> indeed make sense to have a sanity check here.
> However, it is not as easy as simply checking the
> end against __pa(high_memory). Some systems have
> non-contiguous physical memory ranges, with gaps
> of invalid addresses in-between.
The invalid physical address means that it is used as
io mapped. not in system ram region. /dev/mem is not
access to them , is it right?
> You would have to make sure that both the beginning
> and the end are valid, and that there are no gaps of
> invalid pfns in the middle...
If it is limited in system ram, we can walk the resource
to exclude them. or adding pfn_valid further to optimize.
whether other situation should be consider ? I am not sure.
> At that point, is the complexity so much that it no
> longer makes sense to try to protect against root
> crashing the system?
your suggestion is to let the issue along without any protection.
just root user know what they are doing.