linux-kernel - Re: [RFC PATCH] powerpc/mm: Implement STRICT_MODULE

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Message-ID: <6a90db30c8543d547ab8543fbdba02f7fe6a4898.camel@russell.cc>
Date:   Tue, 21 May 2019 14:33:17 +1000
From:   Russell Currey <ruscur@...sell.cc>
To:     Christophe Leroy <christophe.leroy@....fr>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [RFC PATCH] powerpc/mm: Implement STRICT_MODULE_RWX

On Wed, 2019-05-15 at 06:20 +0000, Christophe Leroy wrote:

Confirming this works on hash and radix book3s64.

> +
> +	// only operate on VM areas for now
> +	area = find_vm_area((void *)addr);
> +	if (!area || end > (unsigned long)area->addr + area->size ||
> +	    !(area->flags & VM_ALLOC))
> +		return -EINVAL;

https://lore.kernel.org/patchwork/project/lkml/list/?series=391470

With this patch, the above series causes crashes on (at least) Hash,
since it adds another user of change_page_rw() and change_page_nx()
that for reasons I don't understand yet, we can't handle.  I can work
around this with:

	if (area->flags & VM_FLUSH_RESET_PERMS)
		return 0;

so this is broken on at least one platform as of 5.2-rc1.  We're going
to look into this more to see if there's anything else we have to do as
a result of this series before the next merge window, or if just
working around it like this is good enough.

- Russell