On Tue, Apr 14, 2020 at 02:08:14PM -0500, Josh Poimboeuf wrote: > On Tue, Apr 14, 2020 at 08:27:26PM +0200, Peter Zijlstra wrote: > > On Tue, Apr 14, 2020 at 11:28:36AM -0500, Josh Poimboeuf wrote: > > > Better late than never, these patches add simplifications and > > > improvements for some issues Peter found six months ago, as part of his > > > non-writable text code (W^X) cleanups. > > > > Excellent stuff, thanks!! > > > > I'll go brush up these two patches then: > > > > https://lkml.kernel.org/r/20191018074634.801435443@xxxxxxxxxxxxx > > https://lkml.kernel.org/r/20191018074634.858645375@xxxxxxxxxxxxx > > Ah right, I meant to bring that up. I actually played around with those > patches. While it would be nice to figure out a way to converge the > ftrace module init, I didn't really like the first patch. ftrace only needs it done after ftrace_module_enable(), which is before the notifier chain happens, so we can simply do something like so instead: diff --git a/kernel/module.c b/kernel/module.c index a3a8f6d0e144..89f8d02c3c3e 100644 --- a/kernel/module.c +++ b/kernel/module.c @@ -3700,6 +3700,10 @@ static int prepare_coming_module(struct module *mod) if (err) return err; + module_enable_ro(mod, false); + module_enable_nx(mod); + module_enable_x(mod); + err = blocking_notifier_call_chain_robust(&module_notify_list, MODULE_STATE_COMING, MODULE_STATE_GOING, mod); err = notifier_to_errno(err); @@ -3845,10 +3849,6 @@ static int load_module(struct load_info *info, const char __user *uargs, if (err) goto bug_cleanup; - module_enable_ro(mod, false); - module_enable_nx(mod); - module_enable_x(mod); - /* Module is ready to execute: parsing args may do that. */ after_dashes = parse_args(mod->name, mod->args, mod->kp, mod->num_kp, -32768, 32767, mod, > It bothers me that both the notifiers and the module init() both see the > same MODULE_STATE_COMING state, but only in the former case is the text > writable. > > I think it's cognitively simpler if MODULE_STATE_COMING always means the > same thing, like the comments imply, "fully formed" and thus > not-writable: > > enum module_state { > MODULE_STATE_LIVE, /* Normal state. */ > MODULE_STATE_COMING, /* Full formed, running module_init. */ > MODULE_STATE_GOING, /* Going away. */ > MODULE_STATE_UNFORMED, /* Still setting it up. */ > }; > > And, it keeps tighter constraints on what a notifier can do, which is a > good thing if we can get away with it. Moo! -- but jump_label and static_call are on the notifier chain and I was hoping to make it cheaper for them. Should we perhaps weane them off the notifier and, like ftrace/klp put in explicit calls? It'd make the error handling in prepare_coming_module() a bigger mess, but it should work.
