From 6afbdd059c27330eccbd85943354f94c2b83a7fe Mon Sep 17 00:00:00 2001
From: Rusty Russell <rusty@rustcorp.com.au>
Date: Mon, 30 Mar 2009 21:55:23 -0600
Subject: [PATCH] lguest: fix spurious BUG_ON() on invalid guest stack.
Impact: fix crash on misbehaving guest
gpte_addr() contains a BUG_ON(), insisting that the present flag is
set. We need to return before we call it if that isn't the case.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: stable@kernel.org
---
drivers/lguest/page_tables.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/drivers/lguest/page_tables.c b/drivers/lguest/page_tables.c
index 576a8318221c..82ff484bd8c8 100644
--- a/drivers/lguest/page_tables.c
+++ b/drivers/lguest/page_tables.c
@@ -373,8 +373,10 @@ unsigned long guest_pa(struct lg_cpu *cpu, unsigned long vaddr)
/* First step: get the top-level Guest page table entry. */
gpgd = lgread(cpu, gpgd_addr(cpu, vaddr), pgd_t);
/* Toplevel not present? We can't map it in. */
- if (!(pgd_flags(gpgd) & _PAGE_PRESENT))
+ if (!(pgd_flags(gpgd) & _PAGE_PRESENT)) {
kill_guest(cpu, "Bad address %#lx", vaddr);
+ return -1UL;
+ }
gpte = lgread(cpu, gpte_addr(gpgd, vaddr), pte_t);
if (!(pte_flags(gpte) & _PAGE_PRESENT))
--
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