Xen/x86: don't bail early from clear_foreign_p2m_mapping()

stable inclusion
from stable-5.10.18
commit 740f4d9d0c34ea99279acf2fc99ae33c0142265a
bugzilla: 50148

--------------------------------

commit a35f2ef3 upstream.

Its sibling (set_foreign_p2m_mapping()) as well as the sibling of its
only caller (gnttab_map_refs()) don't clean up after themselves in case
of error. Higher level callers are expected to do so. However, in order
for that to really clean up any partially set up state, the operation
should not terminate upon encountering an entry in unexpected state. It
is particularly relevant to notice here that set_foreign_p2m_mapping()
would skip setting up a p2m entry if its grant mapping failed, but it
would continue to set up further p2m entries as long as their mappings
succeeded.

Arguably down the road set_foreign_p2m_mapping() may want its page state
related WARN_ON() also converted to an error return.

This is part of XSA-361.
Signed-off-by: NJan Beulich <jbeulich@suse.com>
Cc: stable@vger.kernel.org
Reviewed-by: NJuergen Gross <jgross@suse.com>
Signed-off-by: NJuergen Gross <jgross@suse.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Acked-by: NXie XiuQi <xiexiuqi@huawei.com>

arch/x86/xen/p2m.c

@@ -750,17 +750,15 @@ int clear_foreign_p2m_mapping(struct gnttab_unmap_grant_ref *unmap_ops,
 		unsigned long mfn = __pfn_to_mfn(page_to_pfn(pages[i]));
 		unsigned long pfn = page_to_pfn(pages[i]);
 
-		if (mfn == INVALID_P2M_ENTRY || !(mfn & FOREIGN_FRAME_BIT)) {
+		if (mfn != INVALID_P2M_ENTRY && (mfn & FOREIGN_FRAME_BIT))
+			set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
+		else
 			ret = -EINVAL;
-			goto out;
-		}
-
-		set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
 	}
 	if (kunmap_ops)
 		ret = HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref,
-						kunmap_ops, count);
-out:
+						kunmap_ops, count) ?: ret;
+
 	return ret;
 }
 EXPORT_SYMBOL_GPL(clear_foreign_p2m_mapping);