linux-kernel - [PATCH] Xen/gntdev: don't ignore kernel unmapping error

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Message-ID: <c2513395-74dc-aea3-9192-fd265aa44e35@suse.com>
Date:   Fri, 17 Sep 2021 08:13:08 +0200
From:   Jan Beulich <jbeulich@...e.com>
To:     Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:     Stefano Stabellini <sstabellini@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>
Subject: [PATCH] Xen/gntdev: don't ignore kernel unmapping error

While working on XSA-361 and its follow-ups, I failed to spot another
place where the kernel mapping part of an operation was not treated the
same as the user space part. Detect and propagate errors and add a 2nd
pr_debug().

Signed-off-by: Jan Beulich <jbeulich@...e.com>
---
It is of course questionable whether zapping handles even upon failure
is the best course of action. Otoh unmapping shouldn't normally fail
unless there's a bug elsewhere (which is how I came to notice this
discrepancy).

--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -396,6 +396,14 @@ static int __unmap_grant_pages(struct gn
 			map->unmap_ops[offset+i].handle,
 			map->unmap_ops[offset+i].status);
 		map->unmap_ops[offset+i].handle = INVALID_GRANT_HANDLE;
+		if (use_ptemod) {
+			if (map->kunmap_ops[offset+i].status)
+				err = -EINVAL;
+			pr_debug("kunmap handle=%u st=%d\n",
+				 map->kunmap_ops[offset+i].handle,
+				 map->kunmap_ops[offset+i].status);
+			map->kunmap_ops[offset+i].handle = INVALID_GRANT_HANDLE;
+		}
 	}
 	return err;
 }