linux-kernel - Re: [PATCH] iommu/iova: Don't BUG on invalid PFNs

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Date:   Wed, 10 Jun 2020 14:57:00 +0530
From:   guptap@...eaurora.org
To:     Robin Murphy <robin.murphy@....com>
Cc:     joro@...tes.org, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] iommu/iova: Don't BUG on invalid PFNs

On 2020-06-02 18:38, Robin Murphy wrote:
> Unlike the other instances which represent a complete loss of
> consistency within the rcache mechanism itself, or a fundamental
> and obvious misconfiguration by an IOMMU driver, the BUG_ON() in
> iova_magazine_free_pfns() can be provoked at more or less any time
> in a "spooky action-at-a-distance" manner by any old device driver
> passing nonsense to dma_unmap_*() which then propagates through to
> queue_iova().
> 
> Not only is this well outside the IOVA layer's control, it's also
> nowhere near fatal enough to justify panicking anyway - all that
> really achieves is to make debugging the offending driver more
> difficult. Let's simply WARN and otherwise ignore bogus PFNs.
> 
> Reported-by: Prakash Gupta <guptap@...eaurora.org>
> Signed-off-by: Robin Murphy <robin.murphy@....com>
> ---
>  drivers/iommu/iova.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 

Copying stable@...r.kernel.org

You can add
Reviewed-by: Prakash Gupta <guptap@...eaurora.org>

> diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
> index 0e6a9536eca6..612cbf668adf 100644
> --- a/drivers/iommu/iova.c
> +++ b/drivers/iommu/iova.c
> @@ -811,7 +811,9 @@ iova_magazine_free_pfns(struct iova_magazine *mag,
> struct iova_domain *iovad)
>  	for (i = 0 ; i < mag->size; ++i) {
>  		struct iova *iova = private_find_iova(iovad, mag->pfns[i]);
> 
> -		BUG_ON(!iova);
> +		if (WARN_ON(!iova))
> +			continue;
> +
>  		private_free_iova(iovad, iova);
>  	}