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

commit 83a35114d0e4583e6b0ca39502e68b6a92e2910c upstream.

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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/lguest/core.c b/drivers/lguest/core.c
index b5fdcb7..34842e5 100644 (file)
--- a/drivers/lguest/core.c
+++ b/drivers/lguest/core.c
@@ -171,7 +171,7 @@ 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);
 }
 
 /*