From 61c73af08b4ede1fc8cfd2cf72661e6c7cfdbeaa Mon Sep 17 00:00:00 2001 From: Julien Grall Date: Wed, 2 Oct 2019 10:55:07 +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. This is part of XSA-301. Reported-by: Julien Grall Signed-off-by: Julien Grall --- xen/arch/arm/p2m.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c index c7e049901d..af3515df42 100644 --- a/xen/arch/arm/p2m.c +++ b/xen/arch/arm/p2m.c @@ -318,7 +318,12 @@ 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++ ) { -- 2.11.0