On 2017/5/9 23:46, Rik van Riel wrote: > 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. > Hi Rik, Do you mean IO space is allowed to access from mmap /dev/mem? Thanks, Xishi Qiu >>> 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. > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
