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

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Date:   Tue,  2 Jun 2020 14:08:18 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     joro@...tes.org
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Prakash Gupta <guptap@...eaurora.org>
Subject: [PATCH] iommu/iova: Don't BUG on invalid PFNs

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(-)

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);
 	}

-- 
2.23.0.dirty