linux-kernel - Re: [PATCH v4] xen: detect uninitialized xenbus in xenbus

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Date:   Wed, 24 Nov 2021 08:33:00 +0100
From:   Jan Beulich <jbeulich@...e.com>
To:     Stefano Stabellini <sstabellini@...nel.org>
Cc:     boris.ostrovsky@...cle.com, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org,
        Stefano Stabellini <stefano.stabellini@...inx.com>,
        stable@...r.kernel.org, jgross@...e.com
Subject: Re: [PATCH v4] xen: detect uninitialized xenbus in xenbus_init

On 23.11.2021 22:07, Stefano Stabellini wrote:
> From: Stefano Stabellini <stefano.stabellini@...inx.com>
> 
> If the xenstore page hasn't been allocated properly, reading the value
> of the related hvm_param (HVM_PARAM_STORE_PFN) won't actually return
> error. Instead, it will succeed and return zero. Instead of attempting
> to xen_remap a bad guest physical address, detect this condition and
> return early.
> 
> Note that although a guest physical address of zero for
> HVM_PARAM_STORE_PFN is theoretically possible, it is not a good choice
> and zero has never been validly used in that capacity.
> 
> Also recognize all bits set as an invalid value.
> 
> For 32-bit Linux, any pfn above ULONG_MAX would get truncated. Pfns
> above ULONG_MAX should never be passed by the Xen tools to HVM guests
> anyway, so check for this condition and return early.
> 
> Cc: stable@...r.kernel.org
> Signed-off-by: Stefano Stabellini <stefano.stabellini@...inx.com>

Reviewed-by: Jan Beulich <jbeulich@...e.com>