[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] xen/x86: Remap text/data/bss with appropriate permissions
On 17/03/16 15:32, Jan Beulich wrote: >>>> On 17.03.16 at 15:44, <andrew.cooper3@xxxxxxxxxx> wrote: >> On 17/03/16 14:31, Jan Beulich wrote: >>> Also - do we really want to make this code dependent on >>> map_pages_to_xen() not intermediately zapping the mappings >>> being changed? >> Do you mean "immediately"? > No. > >> As far as I can tell, it is guaranteed to be safe, even when remapping >> the code section. Updates to the live pagetables are using atomic >> writes, and I didn't spot a point which would end up with a transient >> non-present mapping. > But we may, at some point and for whatever reason, come to make > the function zap the mapping (i.e. clear the present bit), flush, and > only the re-establish the new mapping. This change is temporary until I can fix the legacy boot issue and reintroduce the proper 2M functionality. If someone in the future wants to change the behaviour of map_pages_to_xen() then we can reconsider. However, I think it is unlikely that this will actually happen at all, and if it ever does, I hope to have already fixed the 2M alignment and deleted this change. This change is a big security improvement, and absolutely should be taken, especially as the current implementation of map_pages_to_xen() is safe. ~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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