linux-hardening - Re: [RFC][PATCH] lkdtm/usercopy: Add tests for other memory types

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Date:   Thu, 12 May 2022 19:56:13 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [RFC][PATCH] lkdtm/usercopy: Add tests for other memory types

On Thu, May 12, 2022 at 11:36:13AM -0700, Kees Cook wrote:
> +static void lkdtm_USERCOPY_FOLIO(void)
> +{
> +	struct folio *folio;
> +	void *addr;
> +
> +	/*
> +	 * FIXME: Folio checking currently misses 0-order allocations, so
> +	 * allocate and bump forward to the last page.
> +	 */
> +	folio = folio_alloc(GFP_KERNEL | __GFP_ZERO, 1);
> +	if (!folio) {
> +		pr_err("folio_alloc() failed!?\n");
> +		return;
> +	}
> +	addr = page_address(&folio->page);

Ideally, code shouldn't be using &folio->page.  If it is, we have a
gap in the folio API.  Fortunately, we have folio_address().

> +	if (addr) {
> +		do_usercopy_page_span("folio", addr + PAGE_SIZE);
> +	}
> +	folio_put(folio);
> +}

Other than that, this looks sane to me.