From 060c2dd3b7c2674a019d94afb2b4ebf3663f6c6e Mon Sep 17 00:00:00 2001 From: Julien Grall 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 Signed-off-by: Julien Grall Reviewed-by: Stefano Stabellini --- 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