Patch-mainline: v5.12-rc2
Git-commit: 8310b77b48c5558c140e7a57a702e7819e62f04e
References: bsc#1183022 XSA-367 CVE-2021-28038
From: Jan Beulich <jbeulich@suse.com>
Date: Thu, 25 Feb 2021 16:34:43 +0100
Subject: [PATCH] Xen/gnttab: handle p2m update errors on a per-slot basis

Bailing immediately from set_foreign_p2m_mapping() upon a p2m updating
error leaves the full batch in an ambiguous state as far as the caller
is concerned. Instead flags respective slots as bad, unmapping what
was mapped there right away.

HYPERVISOR_grant_table_op()'s return value and the individual unmap
slots' status fields get used only for a one-time - there's not much we
can do in case of a failure.

Note that there's no GNTST_enomem or alike, so GNTST_general_error gets
used.

The map ops' handle fields get overwritten just to be on the safe side.

This is part of XSA-367.

Cc: <stable@vger.kernel.org>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/96cccf5d-e756-5f53-b91a-ea269bfb9be0@suse.com
Signed-off-by: Juergen Gross <jgross@suse.com>
---
 arch/arm/xen/p2m.c | 35 +++++++++++++++++++++++++++++++----
 arch/x86/xen/p2m.c | 44 +++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 72 insertions(+), 7 deletions(-)

diff --git a/arch/arm/xen/p2m.c b/arch/arm/xen/p2m.c
index fd6e3aafe272..acb464547a54 100644
--- a/arch/arm/xen/p2m.c
+++ b/arch/arm/xen/p2m.c
@@ -93,12 +93,39 @@ int set_foreign_p2m_mapping(struct gnttab_map_grant_ref *map_ops,
 	int i;
 
 	for (i = 0; i < count; i++) {
+		struct gnttab_unmap_grant_ref unmap;
+		int rc;
+
 		if (map_ops[i].status)
 			continue;
-		if (unlikely(!set_phys_to_machine(map_ops[i].host_addr >> XEN_PAGE_SHIFT,
-				    map_ops[i].dev_bus_addr >> XEN_PAGE_SHIFT))) {
-			return -ENOMEM;
-		}
+		if (likely(set_phys_to_machine(map_ops[i].host_addr >> XEN_PAGE_SHIFT,
+				    map_ops[i].dev_bus_addr >> XEN_PAGE_SHIFT)))
+			continue;
+
+		/*
+		 * Signal an error for this slot. This in turn requires
+		 * immediate unmapping.
+		 */
+		map_ops[i].status = GNTST_general_error;
+		unmap.host_addr = map_ops[i].host_addr,
+		unmap.handle = map_ops[i].handle;
+		map_ops[i].handle = ~0;
+		if (map_ops[i].flags & GNTMAP_device_map)
+			unmap.dev_bus_addr = map_ops[i].dev_bus_addr;
+		else
+			unmap.dev_bus_addr = 0;
+
+		/*
+		 * Pre-populate the status field, to be recognizable in
+		 * the log message below.
+		 */
+		unmap.status = 1;
+
+		rc = HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref,
+					       &unmap, 1);
+		if (rc || unmap.status != GNTST_okay)
+			pr_err_once("gnttab unmap failed: rc=%d st=%d\n",
+				    rc, unmap.status);
 	}
 
 	return 0;
diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
index b5949e5a83ec..9545b8df5315 100644
--- a/arch/x86/xen/p2m.c
+++ b/arch/x86/xen/p2m.c
@@ -710,6 +710,8 @@ int set_foreign_p2m_mapping(struct gnttab_map_grant_ref *map_ops,
 
 	for (i = 0; i < count; i++) {
 		unsigned long mfn, pfn;
+		struct gnttab_unmap_grant_ref unmap[2];
+		int rc;
 
 		/* Do not add to override if the map failed. */
 		if (map_ops[i].status != GNTST_okay ||
@@ -727,10 +729,46 @@ int set_foreign_p2m_mapping(struct gnttab_map_grant_ref *map_ops,
 
 		WARN(pfn_to_mfn(pfn) != INVALID_P2M_ENTRY, "page must be ballooned");
 
-		if (unlikely(!set_phys_to_machine(pfn, FOREIGN_FRAME(mfn)))) {
-			ret = -ENOMEM;
-			goto out;
+		if (likely(set_phys_to_machine(pfn, FOREIGN_FRAME(mfn))))
+			continue;
+
+		/*
+		 * Signal an error for this slot. This in turn requires
+		 * immediate unmapping.
+		 */
+		map_ops[i].status = GNTST_general_error;
+		unmap[0].host_addr = map_ops[i].host_addr,
+		unmap[0].handle = map_ops[i].handle;
+		map_ops[i].handle = ~0;
+		if (map_ops[i].flags & GNTMAP_device_map)
+			unmap[0].dev_bus_addr = map_ops[i].dev_bus_addr;
+		else
+			unmap[0].dev_bus_addr = 0;
+
+		if (kmap_ops) {
+			kmap_ops[i].status = GNTST_general_error;
+			unmap[1].host_addr = kmap_ops[i].host_addr,
+			unmap[1].handle = kmap_ops[i].handle;
+			kmap_ops[i].handle = ~0;
+			if (kmap_ops[i].flags & GNTMAP_device_map)
+				unmap[1].dev_bus_addr = kmap_ops[i].dev_bus_addr;
+			else
+				unmap[1].dev_bus_addr = 0;
 		}
+
+		/*
+		 * Pre-populate both status fields, to be recognizable in
+		 * the log message below.
+		 */
+		unmap[0].status = 1;
+		unmap[1].status = 1;
+
+		rc = HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref,
+					       unmap, 1 + !!kmap_ops);
+		if (rc || unmap[0].status != GNTST_okay ||
+		    unmap[1].status != GNTST_okay)
+			pr_err_once("gnttab unmap failed: rc=%d st0=%d st1=%d\n",
+				    rc, unmap[0].status, unmap[1].status);
 	}
 
 out:
-- 
2.26.2