linux-kernel - Re: [PATCH v2 1/5] irq: set {msi_domain,syscore}_ops as __ro_after

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Date:   Sat, 11 Feb 2017 13:00:16 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Jess Frazelle <me@...sfraz.com>
cc:     Marc Zyngier <marc.zyngier@....com>,
        "open list:IRQ SUBSYSTEM" <linux-kernel@...r.kernel.org>,
        kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH v2 1/5] irq: set {msi_domain,syscore}_ops as
 __ro_after_init

On Sat, 11 Feb 2017, Jess Frazelle wrote:
> On February 11, 2017 1:14:52 AM PST, Thomas Gleixner <tglx@...utronix.de> wrote:
> >The same is true for cpuhotunplug operations.
> 
> This makes sense. Will remove.

That's true for all other patches touching sysops as well. But instead of
giving up I'd recommend to look into the following:

Go through all callsites which use un/register_syscore_ops() and figure out
how many of them are possibly called post init. From a quick grep I can
only find the KVM module, but there might be more.

Lets assume it's KVM only. So you could do the following:

Put something like this into virt/kvm/kvm_main.c, which is a builtin file

static struct syscore_ops ops __ro_after_init = {
       ....
};

int __init foo()
{
    register_ops(&ops);
}

and because we know that kvm is single instance you can just have:

static struct syscore_ops *kvm_ops;

void kvm_set_sysop(*vmx_ops)
{
	kvm_ops = ops;
}

and then have the kvm_syscore callbacks:

static callback()
{
	if (kvm_ops)
	   kvm_ops->callback()
}

Sanity checks and serialization omitted. Then switch kvm_exit/init over to
it.

After that you can make all syscore_ops __ro_after_init, remove the export
from (un)register_syscore_ops() and make that __init.

Not much of an effort and probably worth the trouble.

Thanks,

	tglx