From 3b896936f7505e929dd869d14afcb185d0ee75f8 Mon Sep 17 00:00:00 2001 From: Julien Grall Date: Tue, 15 Oct 2019 17:10:41 +0100 Subject: [PATCH 2/3] xen/arm: p2m: Avoid off-by-one check on p2m->max_mapped_gfn The code base is using inconsistently the field p2m->max_mapped_gfn. Some of the useres expect that p2m->max_guest_gfn contain the highest mapped GFN while others expect highest + 1. p2m->max_guest_gfn is set as highest + 1, because of that the sanity check on the GFN in p2m_resolved_translation_fault() and p2m_get_entry() can be bypassed when GFN == p2m->max_guest_gfn. p2m_get_root_pointer(p2m->max_guest_gfn) may return NULL if it is outside of address range supported and therefore the BUG_ON() could be hit. The current value hold in p2m->max_mapped_gfn is inconsistent with the expectation of the common code (see domain_get_maximum_gpfn()) and also the documentation of the field. Rather than changing the check in p2m_translation_fault() and p2m_get_entry(), p2m->max_mapped_gfn is now containing the highest mapped GFN and the callers assuming "highest + 1" are now adjusted. Take the opportunity to use 1UL rather than 1 as page_order could theoritically big enough to overflow a 32-bit integer. Lastly, the documentation of the field max_guest_gfn to reflect how it is computed. This is part of XSA-301. Reported-by: Julien Grall Signed-off-by: Julien Grall Reviewed-by: Stefano Stabellini --- xen/arch/arm/p2m.c | 6 +++--- xen/include/asm-arm/p2m.h | 5 +---- 2 files changed, 4 insertions(+), 7 deletions(-) diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c index d0045a8b28..8d20d27961 100644 --- a/xen/arch/arm/p2m.c +++ b/xen/arch/arm/p2m.c @@ -1041,7 +1041,7 @@ static int __p2m_set_entry(struct p2m_domain *p2m, p2m_write_pte(entry, pte, p2m->clean_pte); p2m->max_mapped_gfn = gfn_max(p2m->max_mapped_gfn, - gfn_add(sgfn, 1 << page_order)); + gfn_add(sgfn, (1UL << page_order) - 1)); p2m->lowest_mapped_gfn = gfn_min(p2m->lowest_mapped_gfn, sgfn); } @@ -1572,7 +1572,7 @@ int relinquish_p2m_mapping(struct domain *d) p2m_write_lock(p2m); start = p2m->lowest_mapped_gfn; - end = p2m->max_mapped_gfn; + end = gfn_add(p2m->max_mapped_gfn, 1); for ( ; gfn_x(start) < gfn_x(end); start = gfn_next_boundary(start, order) ) @@ -1641,7 +1641,7 @@ int p2m_cache_flush_range(struct domain *d, gfn_t *pstart, gfn_t end) p2m_read_lock(p2m); start = gfn_max(start, p2m->lowest_mapped_gfn); - end = gfn_min(end, p2m->max_mapped_gfn); + end = gfn_min(end, gfn_add(p2m->max_mapped_gfn, 1)); next_block_gfn = start; diff --git a/xen/include/asm-arm/p2m.h b/xen/include/asm-arm/p2m.h index 89f82df380..5fdb6e8183 100644 --- a/xen/include/asm-arm/p2m.h +++ b/xen/include/asm-arm/p2m.h @@ -36,10 +36,7 @@ struct p2m_domain { /* Current Translation Table Base Register for the p2m */ uint64_t vttbr; - /* - * Highest guest frame that's ever been mapped in the p2m - * Only takes into account ram and foreign mapping - */ + /* Highest guest frame that's ever been mapped in the p2m */ gfn_t max_mapped_gfn; /* -- 2.23.0