[PATCH] lguest: fix out-by-one error in address checking.

[Rusty Russell <rusty@rustcorp.com.au>]

This bug has been there since day 1; addresses in the top guest
physical page weren't considered valid.  You could map that page (the
check in check_gpte() is correct), but if a guest tried to put a
pagetable there we'd check that address manually when walking it, and
kill the guest.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: stable@kernel.org

diff --git a/drivers/lguest/core.c b/drivers/lguest/core.c
index 7dc93aa004c8..312ffd3d0017 100644
--- a/drivers/lguest/core.c
+++ b/drivers/lguest/core.c
@@ -173,7 +173,7 @@ static void unmap_switcher(void)
 bool lguest_address_ok(const struct lguest *lg,
 		       unsigned long addr, unsigned long len)
 {
-	return (addr+len) / PAGE_SIZE < lg->pfn_limit && (addr+len >= addr);
+	return addr+len <= lg->pfn_limit * PAGE_SIZE && (addr+len >= addr);
 }
 
 /*