From mboxrd@z Thu Jan  1 00:00:00 1970
From: Julien Grall <julien.grall@linaro.org>
Subject: Re: [PATCH V13 3/7] xen/arm: Allow hypervisor access to
 mem_access protected pages
Date: Thu, 12 Mar 2015 13:50:14 +0000
Message-ID: <55019996.9050208@linaro.org>
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To: Tamas K Lengyel <tklengyel@sec.in.tum.de>, xen-devel@lists.xen.org
Cc: wei.liu2@citrix.com, ian.campbell@citrix.com, stefano.stabellini@eu.citrix.com, ian.jackson@eu.citrix.com, tim@xen.org, stefano.stabellini@citrix.com, jbeulich@suse.com, keir@xen.org
List-Id: xen-devel@lists.xenproject.org

Hi Tamas,

On 06/03/15 21:24, Tamas K Lengyel wrote:
> +/*
> + * If mem_access is in use it might have been the reason why get_page_from_gva
> + * failed to fetch the page, as it uses the MMU for the permission checking.
> + * Only in these cases we do a software-based type check and fetch the page if
> + * we indeed found a conflicting mem_access setting.
> + */
> +static int check_type_get_page(vaddr_t gva, unsigned long flag,
> +                               struct page_info** page)
> +{
> +    long rc;
> +    paddr_t ipa;
> +    unsigned long maddr;
> +    unsigned long mfn;
> +    xenmem_access_t xma;
> +    p2m_type_t t;
> +
> +    rc = gva_to_ipa(gva, &ipa);

I though a bit more about this call.

gva_to_ipa only checks if the mapping has read-permission. That would
allow a guest to write on read-only mapping.

You have to pass the flags to gva_to_ipa in order to avoid
re-introducing XSA-98 [1]

Regards,

[1] http://xenbits.xen.org/xsa/advisory-98.html

-- 
Julien Grall