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SubjectRe: [RESENT PATCH] x86/mem: fix the offset overflow when read/write mem
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On Thu, 2017-05-04 at 10:28 +0800, zhong jiang wrote:
> On 2017/5/4 2:46, Rik van Riel wrote:

> > 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?

Not necessarily. Some systems simply have large
gaps in physical memory access. Their memory map
may look like this:

|MMMMMM|IO|MMMM|..................|MMMMMMMM|

Where M is memory, IO is IO space, and the
dots are simply a gap in physical address
space with no valid accesses at all.

> > 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.

Well, root already has other ways to crash the system.

Implementing validation on /dev/mem may make sense if
it can be done in a simple way, but may not be worth
it if it becomes too complex.

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