Messages in this thread | | | Date | Fri, 6 Nov 2015 14:42:46 +0100 | From | Petr Mladek <> | Subject | Re: [PATCH v2 3/3] livepatch: Cleanup module page permission changes |
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On Fri 2015-11-06 06:12:47, Josh Poimboeuf wrote: > On Fri, Nov 06, 2015 at 11:40:55AM +0100, Petr Mladek wrote: > > On Thu 2015-11-05 15:18:05, Josh Poimboeuf wrote: > > > Calling set_memory_rw() and set_memory_ro() for every iteration of the > > > loop in klp_write_object_relocations() is messy, inefficient, and > > > error-prone. > > > > > > Change all the read-only pages to read-write before the loop and convert > > > them back to read-only again afterwards. > > > > > > The {un}set_module_core_ro_nx() functions are used to change the > > > page permissions. Toggling NX isn't necessary in this case, but it's > > > not highly performance sensitive code so it should be fine. > > > > Hmm, the name (un)set_module_core_ro_nx() still sounds a bit strange, > > especially the "ro_nx" suffix. > > > Alternative solution would be to create > > > > set_module_text_rw() > > set_module_text_ro() > > > > There already exists > > > > set_all_modules_text_rw() > > set_all_modules_text_ro() > > > > They modify only the ro/rw flags. IMHO, the name is more descriptive > > They are used by ftrace for very similar purpose. > > That wouldn't be enough. Relocations can occur not only in text, but > also in data. That includes read-only data.
I see. This just shows how this all is confusing. Or maybe I am just dumb :-)
> The (un)set_module_core_ro_nx() naming was taken from the names of > existing module functions (unset_module_{core,init}_ro_nx()). They > enable/disable the CONFIG_DEBUG_SET_MODULE_RONX feature on the core part > of the module. The name makes sense to me, though I'm certainly open to > other ideas.
I think that we should not mix
set_*_ro() set_*_rw()
with
set_*_ro*() unset_*_ro*()
naming schemes. What about adding into the public API?
set_module_ro() set_module_rw()
It should modify everything: init, core, text, and data but only the ro/rw flags.
Sigh, we went quite far from the few lines patch :-/
> > They modify also the init section. But we might want to touch it > > as well. klp_module_notify() is called too late now. But once we > > have a more complex consistency model, we will need to reject > > the module when the patching fails. We will need to call the > > livepatch init earlier, close to ftrace_module_init(mod). > > Then the init section might be interesting as well. > > Init section functions don't have the __fentry() call, so they can't be > patched. If that were to change in the future, we could use the > (un)set_module_init_ro_nx() functions, which already exist.
I see.
Best Regards, Petr
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