linux-kernel - Re: [PATCH v2 01/27] drm/i915/gvt: Verify pfn is "valid" before dereferencing "struct page"

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Date:   Fri, 17 Mar 2023 12:20:09 +0800
From:   Yan Zhao <yan.y.zhao@...el.com>
To:     Sean Christopherson <seanjc@...gle.com>
CC:     Paolo Bonzini <pbonzini@...hat.com>,
        Zhenyu Wang <zhenyuw@...ux.intel.com>,
        Zhi Wang <zhi.a.wang@...el.com>, <kvm@...r.kernel.org>,
        <intel-gvt-dev@...ts.freedesktop.org>,
        <intel-gfx@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>,
        Ben Gardon <bgardon@...gle.com>
Subject: Re: [PATCH v2 01/27] drm/i915/gvt: Verify pfn is "valid" before
 dereferencing "struct page"

Reviewed-by: Yan Zhao <yan.y.zhao@...el.com>

On Fri, Mar 10, 2023 at 04:22:32PM -0800, Sean Christopherson wrote:
> Check that the pfn found by gfn_to_pfn() is actually backed by "struct
> page" memory prior to retrieving and dereferencing the page.  KVM
> supports backing guest memory with VM_PFNMAP, VM_IO, etc., and so
> there is no guarantee the pfn returned by gfn_to_pfn() has an associated
> "struct page".
> 
> Fixes: b901b252b6cf ("drm/i915/gvt: Add 2M huge gtt support")
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  drivers/gpu/drm/i915/gvt/gtt.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/gvt/gtt.c b/drivers/gpu/drm/i915/gvt/gtt.c
> index 4ec85308379a..58b9b316ae46 100644
> --- a/drivers/gpu/drm/i915/gvt/gtt.c
> +++ b/drivers/gpu/drm/i915/gvt/gtt.c
> @@ -1183,6 +1183,10 @@ static int is_2MB_gtt_possible(struct intel_vgpu *vgpu,
>  	pfn = gfn_to_pfn(vgpu->vfio_device.kvm, ops->get_pfn(entry));
>  	if (is_error_noslot_pfn(pfn))
>  		return -EINVAL;
> +
> +	if (!pfn_valid(pfn))
> +		return -EINVAL;
> +
>  	return PageTransHuge(pfn_to_page(pfn));
>  }
>  
> -- 
> 2.40.0.rc1.284.g88254d51c5-goog
>