linux-kernel - Re: [PATCH v5] drm/i915/gvt: fix double free bug in split_2MB_gtt

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Date:   Wed, 21 Dec 2022 10:58:57 +0800
From:   Zhenyu Wang <zhenyuw@...ux.intel.com>
To:     Zheng Wang <zyytlz.wz@....com>
Cc:     zhi.a.wang@...el.com, alex000young@...il.com, security@...nel.org,
        intel-gvt-dev@...ts.freedesktop.org,
        tvrtko.ursulin@...ux.intel.com, airlied@...ux.ie,
        gregkh@...uxfoundation.org, intel-gfx@...ts.freedesktop.org,
        joonas.lahtinen@...ux.intel.com, hackerzheng666@...il.com,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        1002992920@...com, zhenyuw@...ux.intel.com, airlied@...il.com
Subject: Re: [PATCH v5] drm/i915/gvt: fix double free bug in
 split_2MB_gtt_entry

On 2022.12.20 17:40:14 +0800, Zheng Wang wrote:
> If intel_gvt_dma_map_guest_page failed, it will call
>  ppgtt_invalidate_spt, which will finally free the spt. But the
>  caller function ppgtt_populate_spt_by_guest_entry does not notice
>  that, it will free spt again in its error path.

indent

> 
> Fix this by undoing the mapping of DMA address and freeing sub_spt.
> Besides, leave the handle of spt destroy to caller function instead of
> callee function when error occurs.
> 
> Fixes: b901b252b6cf ("drm/i915/gvt: Add 2M huge gtt support")
> Signed-off-by: Zheng Wang <zyytlz.wz@....com>
> ---
> v5:
> - remove unnecessary switch-case code for there is only one particular case,
> correct the unmap target from parent_spt to sub_spt.add more details in
> commit message. All suggested by Zhenyu
> 
> v4:
> - fix by undo the mapping of DMA address and free sub_spt suggested by Zhi
> 
> v3:
> - correct spelling mistake and remove unused variable suggested by Greg
> 
> v2: https://lore.kernel.org/all/20221006165845.1735393-1-zyytlz.wz@163.com/
> 
> v1: https://lore.kernel.org/all/20220928033340.1063949-1-zyytlz.wz@163.com/
> ---
>  drivers/gpu/drm/i915/gvt/gtt.c | 18 ++++++++++++++----
>  1 file changed, 14 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gvt/gtt.c b/drivers/gpu/drm/i915/gvt/gtt.c
> index 51e5e8fb505b..4d478a59eb7d 100644
> --- a/drivers/gpu/drm/i915/gvt/gtt.c
> +++ b/drivers/gpu/drm/i915/gvt/gtt.c
> @@ -1209,10 +1209,8 @@ static int split_2MB_gtt_entry(struct intel_vgpu *vgpu,
>  	for_each_shadow_entry(sub_spt, &sub_se, sub_index) {
>  		ret = intel_gvt_dma_map_guest_page(vgpu, start_gfn + sub_index,
>  						   PAGE_SIZE, &dma_addr);
> -		if (ret) {
> -			ppgtt_invalidate_spt(spt);
> -			return ret;
> -		}
> +		if (ret)
> +			goto err;
>  		sub_se.val64 = se->val64;
>  
>  		/* Copy the PAT field from PDE. */
> @@ -1231,6 +1229,18 @@ static int split_2MB_gtt_entry(struct intel_vgpu *vgpu,
>  	ops->set_pfn(se, sub_spt->shadow_page.mfn);
>  	ppgtt_set_shadow_entry(spt, se, index);
>  	return 0;
> +err:
> +	/* Undone the existing mappings of DMA addr. */

We need a verb here for Undo.

> +	for_each_present_shadow_entry(sub_spt, &sub_se, sub_index) {
> +		gvt_vdbg_mm("invalidate 4K entry\n");
> +		ppgtt_invalidate_pte(sub_spt, &sub_se);
> +	}
> +	/* Release the new allocated spt. */
> +	trace_spt_change(sub_spt->vgpu->id, "release", sub_spt,
> +		sub_spt->guest_page.gfn, sub_spt->shadow_page.type);
> +	ppgtt_free_spt(sub_spt);
> +	sub_spt = NULL;

Not need to reset local variable that has no use then.

I'll handle these trivial fixes during the merge.

Reviewed-by: Zhenyu Wang <zhenyuw@...ux.intel.com>

thanks

> +	return ret;
>  }
>  
>  static int split_64KB_gtt_entry(struct intel_vgpu *vgpu,
> -- 
> 2.25.1
> 

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