On Fri, Apr 05, 2013 at 05:29:32AM +0100, Al Viro wrote: > 4) nasty semantics issue - mmap() vs. revoke (of any sort, including > remove_proc_entry(), etc.). Suppose a revokable file had been mmapped; > now it's going away. What should we do to its VMAs? Right now sysfs > and procfs get away with that, but only because there's only one thing > that has ->mmap() there - /proc/bus/pci and sysfs equivalents. I've > no idea how does pci_mmap_page_range() interact with PCI hotplug (and > I'm not at all sure that whatever it does isn't racy wrt device removal), > but I suspect that it strongly depends on lack of ->fault() for those > VMAs, which makes killing all PTEs pointing to pages in question enough. > How generic do we want to make it? Anybody wanting to add more files > that could be mmapped in procfs/sysfs/debugfs deserves to be hurt, but > if we start playing with revoke(2), restriction might become inconvenient. > I'm not sure what kind of behaviour do we want there - *BSD at least > used to have revoke(2) only for character devices that had no mmap()... I am seeing possible problems in software implementing their own memory management ontop SIGSEGV e.g. java. I hope they sanely distinguish between heap mappings and file mmaps. FreeBSD allowes tearing down a mmap on MAC security relabel. Two possible actions are available: SIGSEGV generation by tearing down the mapping forcefully or enable some kind of copy-on-write semantics on revoke: http://svnweb.freebsd.org/base/head/sys/security/mac/mac_process.c?revision=248084&view=markup I like to see something like revoke being worked on, thanks! Greetings, Hannes -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
