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List:       linux-kernel
Subject:    [patch 43/45] lguest: fix spurious BUG_ON() on invalid guest stack.
From:       Chris Wright <chrisw () sous-sol ! org>
Date:       2009-03-31 23:11:28
Message-ID: 20090331231809.935405052 () sous-sol ! org
[Download RAW message or body]

-stable review patch.  If anyone has any objections, please let us know.
---------------------

From: Rusty Russell <rusty@rustcorp.com.au>

upstream commit: 6afbdd059c27330eccbd85943354f94c2b83a7fe

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
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
---
 drivers/lguest/page_tables.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/drivers/lguest/page_tables.c
+++ b/drivers/lguest/page_tables.c
@@ -373,8 +373,10 @@ unsigned long guest_pa(struct lg_cpu *cp
 	/* 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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