Messages in this thread | | | Date | Wed, 7 May 2014 11:43:19 -0500 | From | Josh Poimboeuf <> | Subject | Re: [RFC PATCH 0/2] kpatch: dynamic kernel patching |
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On Wed, May 07, 2014 at 05:57:54PM +0200, Ingo Molnar wrote: > Live patching does not enter into this question, ever. The correctness > of a patch to the source does not depend on 'live patching' > considerations in any way, shape or form. > > Any mechanism that tries to blur these lines is broken by design. > > My claim is that if a patch is correct/safe in the old fashioned way, > then a fundamental principle is that a live patching subsystem must > either safely apply, or safely reject the live patching attempt, > independently from any user input.
That's a valiant goal, but it's not going to happen unless you want to rewrite Linux in Haskell. It's just not possible for a program to prove that a patch is safe to apply to a running kernel. There are way too many subtle interactions with dynamically allocated data between functions.
I think the only way to achieve that is with CRIU, but it still requires a kexec or a reboot, so you lose all kernel state and it's much more disruptive.
> "We think/hope it won't blow up in most cases and we automated some > checks halfways" or "the user must know what he is doing" is really > not something that I think is a good concept for something as fragile > as live patching.
This is a distro tool, not a general purpose one. If distros are careful with their patch selection, it won't blow up. It's a valuable way for distros to help out sysadmins who need a hot security fix but can't reboot immediately.
-- Josh
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