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From 060c2dd3b7c2674a019d94afb2b4ebf3663f6c6e Mon Sep 17 00:00:00 2001
From: Julien Grall <julien.grall@arm.com>
Date: Tue, 15 Oct 2019 17:10:42 +0100
Subject: [PATCH 3/3] xen/arm: p2m: Don't check the return of
p2m_get_root_pointer() with BUG_ON()
It turns out that the BUG_ON() was actually reachable with well-crafted
hypercalls. The BUG_ON() is here to prevent catch logical error, so
crashing Xen is a bit over the top.
While all the holes should now be fixed, it would be better to downgrade
the BUG_ON() to something less fatal to prevent any more DoS.
The BUG_ON() in p2m_get_entry() is now replaced by ASSERT_UNREACHABLE()
to catch mistake in debug build and return INVALID_MFN for production
build. The interface also requires to set page_order to give an idea of
the size of "hole". So 'level' is now set so we report a hole of size of
the an entry of the root page-table. This stays inline with what happen
when the GFN is higher than p2m->max_mapped_gfn.
The BUG_ON() in p2m_resolve_translation_fault() is now replaced by
ASSERT_UNREACHABLE() to catch mistake in debug build and just report a
fault for producion build.
This is part of XSA-301.
Reported-by: Julien Grall <Julien.Grall@arm.com>
Signed-off-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
---
xen/arch/arm/p2m.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)
diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index 8d20d27961..ce59f2b503 100644
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -395,7 +395,12 @@ mfn_t p2m_get_entry(struct p2m_domain *p2m, gfn_t gfn,
* the table should always be non-NULL because the gfn is below
* p2m->max_mapped_gfn and the root table pages are always present.
*/
- BUG_ON(table == NULL);
+ if ( !table )
+ {
+ ASSERT_UNREACHABLE();
+ level = P2M_ROOT_LEVEL;
+ goto out;
+ }
for ( level = P2M_ROOT_LEVEL; level < 3; level++ )
{
@@ -1196,7 +1201,11 @@ bool p2m_resolve_translation_fault(struct domain *d, gfn_t gfn)
* The table should always be non-NULL because the gfn is below
* p2m->max_mapped_gfn and the root table pages are always present.
*/
- BUG_ON(table == NULL);
+ if ( !table )
+ {
+ ASSERT_UNREACHABLE();
+ goto out;
+ }
/*
* Go down the page-tables until an entry has the valid bit unset or
--
2.23.0
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