Subject: Re: [RFC PATCH 3/7] module: prepare to handle ROX allocations for text

From: Mike Rapoport <[email-masked]>
Date: Thu, 18 Apr 2024 13:20:17 +0300

On Tue, Apr 16, 2024 at 12:36:08PM +0300, Nadav Amit wrote:
> 
> 
> > On 11 Apr 2024, at 19:05, Mike Rapoport <[email-masked]> wrote:
> > 
> > @@ -2440,7 +2479,24 @@ static int post_relocation(struct module *mod, const struct load_info *info)
> > 	add_kallsyms(mod, info);
> > 
> > 	/* Arch-specific module finalizing. */
> > -	return module_finalize(info->hdr, info->sechdrs, mod);
> > +	ret = module_finalize(info->hdr, info->sechdrs, mod);
> > +	if (ret)
> > +		return ret;
> > +
> > +	for_each_mod_mem_type(type) {
> > +		struct module_memory *mem = &mod->mem[type];
> > +
> > +		if (mem->is_rox) {
> > +			if (!execmem_update_copy(mem->base, mem->rw_copy,
> > +						 mem->size))
> > +				return -ENOMEM;
> > +
> > +			vfree(mem->rw_copy);
> > +			mem->rw_copy = NULL;
> > +		}
> > +	}
> > +
> > +	return 0;
> > }
> 
> I might be missing something, but it seems a bit racy.
> 
> IIUC, module_finalize() calls alternatives_smp_module_add(). At this
> point, since you don’t hold the text_mutex, some might do text_poke(),
> e.g., by enabling/disabling static-key, and the update would be
> overwritten. No?

Right :(
Even worse, for UP case alternatives_smp_unlock() will "patch" still empty
area.

So I'm thinking about calling alternatives_smp_module_add() from an
additional callback after the execmem_update_copy().

Does it make sense to you?

-- 
Sincerely yours,
Mike.