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. -- All rights reversed
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