Subject: Re: [PATCH v5 02/10] mm, x86: Add support for eXclusive Page Frame
 Ownership (XPFO)
To: Tycho Andersen <tycho@docker.com>, linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org, kernel-hardening@lists.openwall.com,
        Marco Benatto <marco.antonio.780@gmail.com>,
        Juerg Haefliger <juerg.haefliger@canonical.com>,
        Juerg Haefliger <juerg.haefliger@hpe.com>
References: <20170809200755.11234-1-tycho@docker.com>
 <20170809200755.11234-3-tycho@docker.com>
From: Laura Abbott <labbott@redhat.com>
Message-ID: <bab02094-0c58-fe8f-855c-d67a03d7003a@redhat.com>
Date: Mon, 14 Aug 2017 11:51:02 -0700
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On 08/09/2017 01:07 PM, Tycho Andersen wrote:
> diff --git a/mm/xpfo.c b/mm/xpfo.c
> new file mode 100644
> index 000000000000..3cd45f68b5ad
> --- /dev/null
> +++ b/mm/xpfo.c
> @@ -0,0 +1,208 @@
> +/*
> + * Copyright (C) 2017 Hewlett Packard Enterprise Development, L.P.
> + * Copyright (C) 2016 Brown University. All rights reserved.
> + *
> + * Authors:
> + *   Juerg Haefliger <juerg.haefliger@hpe.com>
> + *   Vasileios P. Kemerlis <vpk@cs.brown.edu>
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms of the GNU General Public License version 2 as published by
> + * the Free Software Foundation.
> + */
> +
> +#include <linux/mm.h>
> +#include <linux/module.h>
> +#include <linux/page_ext.h>
> +#include <linux/xpfo.h>
> +
> +#include <asm/tlbflush.h>
> +
> +/* XPFO page state flags */
> +enum xpfo_flags {
> +	XPFO_PAGE_USER,		/* Page is allocated to user-space */
> +	XPFO_PAGE_UNMAPPED,	/* Page is unmapped from the linear map */
> +};
> +
> +/* Per-page XPFO house-keeping data */
> +struct xpfo {
> +	unsigned long flags;	/* Page state */
> +	bool inited;		/* Map counter and lock initialized */
> +	atomic_t mapcount;	/* Counter for balancing map/unmap requests */
> +	spinlock_t maplock;	/* Lock to serialize map/unmap requests */
> +};
> +
> +DEFINE_STATIC_KEY_FALSE(xpfo_inited);
> +
> +static bool xpfo_disabled __initdata;
> +
> +static int __init noxpfo_param(char *str)
> +{
> +	xpfo_disabled = true;
> +
> +	return 0;
> +}
> +
> +early_param("noxpfo", noxpfo_param);
> +
> +static bool __init need_xpfo(void)
> +{
> +	if (xpfo_disabled) {
> +		printk(KERN_INFO "XPFO disabled\n");
> +		return false;
> +	}
> +
> +	return true;
> +}
> +
> +static void init_xpfo(void)
> +{
> +	printk(KERN_INFO "XPFO enabled\n");
> +	static_branch_enable(&xpfo_inited);
> +}
> +
> +struct page_ext_operations page_xpfo_ops = {
> +	.size = sizeof(struct xpfo),
> +	.need = need_xpfo,
> +	.init = init_xpfo,
> +};
> +
> +static inline struct xpfo *lookup_xpfo(struct page *page)
> +{
> +	return (void *)lookup_page_ext(page) + page_xpfo_ops.offset;
> +}

lookup_page_ext can return NULL so this function and its callers
need to account for that.

Thanks,
Laura