On Fri, Oct 19, 2018 at 02:16:19PM +0200, Miroslav Benes wrote: > On Thu, 18 Oct 2018, Josh Poimboeuf wrote: > > > On Thu, Oct 18, 2018 at 04:54:56PM +0200, Petr Mladek wrote: > > > On Mon 2018-10-15 18:01:43, Miroslav Benes wrote: > > > > On Fri, 12 Oct 2018, Petr Mladek wrote: > > > > > > > > > On Wed 2018-09-05 11:34:06, Miroslav Benes wrote: > > > > > > On Tue, 28 Aug 2018, Petr Mladek wrote: > > > > > > > Also the API and logic is much easier. It is enough to call > > > > > > > klp_enable_patch() in module_init() call. The patch patch can be disabled > > > > > > > by writing '0' into /sys/kernel/livepatch/<patch>/enabled. Then the module > > > > > > > can be removed once the transition finishes and sysfs interface is freed. > > > > > > > > > > > > I think it would be good to discuss our sysfs interface here as well. > > > > > > > > > > > > Writing '1' to enabled attribute now makes sense only when you need to > > > > > > reverse an unpatching transition. Writing '0' means "disable" or a > > > > > > reversion again. > > > > > > > > > > > > Wouldn't be better to split it to two different attributes? Something like > > > > > > "disable" and "reverse"? It could be more intuitive. > > > > > > > > > > > > Maybe we'd also find out that even patch->enabled member is not useful > > > > > > anymore in such case. > > > > > > > > > > I though about this as well. I kept "enabled" because: > > > > > > > > > > + It keeps the public interface the same as before. Most people > > > > > would not notice any change in the behavior except maybe that > > > > > the interface disappears when the patch gets disabled. > > > > > > > > Well our sysfs interface is still in a testing phase as far as ABI is > > > > involved. Moreover, each live patch is bound to its base kernel by > > > > definition anyway. So we can change this without remorse, I think. > > > > But it would break tooling, which is not kernel specific. I'm not sure > > whether it would be worth the headache. After all I think the livepatch > > sysfs interface is designed for tools, not humans. > > You're right. It's probably not worth it. Oh well. > > > > > > + The reverse operation makes most sense when the transition > > > > > cannot get finished. In theory, it might be problem to > > > > > finish even the reversed one. People might want to > > > > > reverse once again and force it. Then "reverse" file > > > > > might be confusing. They might not know in which direction > > > > > they do the reverse. > > > > > > > > I still think it would be better to have a less confusing interface and it > > > > would outweigh the second remark. > > > > > > OK, what about having just "disable" in sysfs. I agree that it makes > > > much more sense than "enable" now. > > > > > > It might be used also for the reverse operation the same way as > > > "enable" was used before. I think that standalone "reverse" might > > > be confusing when we allow to reverse the operation in both > > > directions. > > > > As long as we're talking about radical changes... how about we just > > don't allow disabling patches at all? Instead a patch can be replaced > > with a 'revert' patch, or an empty 'nop' patch. That would make our > > code simpler and also ensure there's an audit trail. > > > > (Apologies if we've already talked about this. My brain is still mushy > > thanks to Spectre and friends.) > > I think we talked about it last year in Prague and I think we convinced > you that it was not a good idea (...not to allow disabling patches at > all). > > BUT! Empty 'nop' patch is a new idea and we may certainly discuss it. I definitely remember talking about it in Prague, but I don't remember any conclusions. My livepatch-related brain cache lines have been flushed thanks to the aforementioned CVEs and my rapidly advancing senility. > > The amount of flexibility we allow is kind of crazy, considering how > > delicate of an operation live patching is. That reminds me that I > > should bring up my other favorite idea at LPC: require modules to be > > loaded before we "patch" them. > > We talked about this as well and if I remember correctly we came to a > conclusion that it is all about a distribution and maintenance. We cannot > ask customers to load modules they do not need just because we need to > patch them. Fair enough. > One cumulative patch is not that great in this case. I remember you > had a crazy idea how to solve it, but I don't remember details. My > notes from the event say... > > - livepatch code complexity > - make it synchronous with respect to modules loading > - Josh's crazy idea > > That's not much :D > > So yes, we can talk about it and hopefully make proper notes this time. Heh, better notes would be good, otherwise I'll just keep complaining about the same things every year :-) I'll try to remember what my crazy idea was, or maybe come up with some new ones to keep it fresh. -- Josh
