linux-kernel - Re: [PATCH 02/12] powerpc/module: Mark module stubs with a magic value

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Date:	Thu, 25 Feb 2016 17:43:58 +1100
From:	Michael Ellerman <mpe@...erman.id.au>
To:	Balbir Singh <bsingharora@...il.com>, linuxppc-dev@...abs.org
Cc:	duwe@....de, linux-kernel@...r.kernel.org, rostedt@...dmis.org,
	kamalesh@...ux.vnet.ibm.com, pmladek@...e.com, jeyu@...hat.com,
	jkosina@...e.cz, live-patching@...r.kernel.org, mbenes@...e.cz
Subject: Re: [PATCH 02/12] powerpc/module: Mark module stubs with a magic
 value

On Thu, 2016-02-25 at 11:04 +1100, Balbir Singh wrote:
>
> On 25/02/16 01:28, Michael Ellerman wrote:
> > -bool is_module_trampoline(u32 *p)
> > +int module_trampoline_target(struct module *mod, unsigned long addr,
> > +			     unsigned long *target)
> >  {
> > -	unsigned int i;
> > -	u32 insns[ARRAY_SIZE(ppc64_stub_insns)];
> > -
> > -	BUILD_BUG_ON(sizeof(ppc64_stub_insns) != sizeof(ppc64_stub_mask));
> > +	struct ppc64_stub_entry *stub;
> > +	func_desc_t funcdata;
> > +	u32 magic;
> >
> > -	if (probe_kernel_read(insns, p, sizeof(insns)))
> > +	if (!within_module_core(addr, mod)) {
> > +		pr_err("%s: stub %lx not in module %s\n", __func__, addr, mod->name);
> >  		return -EFAULT;

> -EFAULT or -EINVAL?

I think we want EFAULT. Otherwise ftrace_bug() will try and print the actual
instruction, which would then fault. (though I haven't confirmed that by
testing)

> I wonder if we can recover from a bad trampoline address.

We can't recover at the moment. Do you mean is there some way we could recover?

cheers