From: Jan Beulich Subject: x86/mm: don't wrongly set page ownership PV domains can obtain mappings of any pages owned by the correct domain, including ones that aren't actually assigned as "normal" RAM, but used by Xen internally. At the moment such "internal" pages marked as owned by a guest include pages used to track logdirty bits, as well as p2m pages and the "unpaged pagetable" for HVM guests. Since the PV memory management and shadow code conflict in their use of struct page_info fields, and since shadow code is being used for log-dirty handling for PV domains, pages coming from the shadow pool must, for PV domains, not have the domain set as their owner. While the change could be done conditionally for just the PV case in shadow code, do it unconditionally (and for consistency also for HAP), just to be on the safe side. There's one special case though for shadow code: The page table used for running a HVM guest in unpaged mode is subject to get_page() (in set_shadow_status()) and hence must have its owner set. This is XSA-248. Signed-off-by: Jan Beulich Reviewed-by: Tim Deegan Reviewed-by: George Dunlap --- v2: Drop PGC_page_table related pieces. --- a/xen/arch/x86/mm/hap/hap.c +++ b/xen/arch/x86/mm/hap/hap.c @@ -286,8 +286,7 @@ static struct page_info *hap_alloc_p2m_p { d->arch.paging.hap.total_pages--; d->arch.paging.hap.p2m_pages++; - page_set_owner(pg, d); - pg->count_info |= 1; + ASSERT(!page_get_owner(pg) && !(pg->count_info & PGC_count_mask)); } else if ( !d->arch.paging.p2m_alloc_failed ) { @@ -302,21 +301,23 @@ static struct page_info *hap_alloc_p2m_p static void hap_free_p2m_page(struct domain *d, struct page_info *pg) { + struct domain *owner = page_get_owner(pg); + /* This is called both from the p2m code (which never holds the * paging lock) and the log-dirty code (which always does). */ paging_lock_recursive(d); - ASSERT(page_get_owner(pg) == d); - /* Should have just the one ref we gave it in alloc_p2m_page() */ - if ( (pg->count_info & PGC_count_mask) != 1 ) { - HAP_ERROR("Odd p2m page %p count c=%#lx t=%"PRtype_info"\n", - pg, pg->count_info, pg->u.inuse.type_info); + /* Should still have no owner and count zero. */ + if ( owner || (pg->count_info & PGC_count_mask) ) + { + HAP_ERROR("d%d: Odd p2m page %"PRI_mfn" d=%d c=%lx t=%"PRtype_info"\n", + d->domain_id, mfn_x(page_to_mfn(pg)), + owner ? owner->domain_id : DOMID_INVALID, + pg->count_info, pg->u.inuse.type_info); WARN(); + pg->count_info &= ~PGC_count_mask; + page_set_owner(pg, NULL); } - pg->count_info &= ~PGC_count_mask; - /* Free should not decrement domain's total allocation, since - * these pages were allocated without an owner. */ - page_set_owner(pg, NULL); d->arch.paging.hap.p2m_pages--; d->arch.paging.hap.total_pages++; hap_free(d, page_to_mfn(pg)); --- a/xen/arch/x86/mm/shadow/common.c +++ b/xen/arch/x86/mm/shadow/common.c @@ -1503,32 +1503,29 @@ shadow_alloc_p2m_page(struct domain *d) pg = mfn_to_page(shadow_alloc(d, SH_type_p2m_table, 0)); d->arch.paging.shadow.p2m_pages++; d->arch.paging.shadow.total_pages--; + ASSERT(!page_get_owner(pg) && !(pg->count_info & PGC_count_mask)); paging_unlock(d); - /* Unlike shadow pages, mark p2m pages as owned by the domain. - * Marking the domain as the owner would normally allow the guest to - * create mappings of these pages, but these p2m pages will never be - * in the domain's guest-physical address space, and so that is not - * believed to be a concern. */ - page_set_owner(pg, d); - pg->count_info |= 1; return pg; } static void shadow_free_p2m_page(struct domain *d, struct page_info *pg) { - ASSERT(page_get_owner(pg) == d); - /* Should have just the one ref we gave it in alloc_p2m_page() */ - if ( (pg->count_info & PGC_count_mask) != 1 ) + struct domain *owner = page_get_owner(pg); + + /* Should still have no owner and count zero. */ + if ( owner || (pg->count_info & PGC_count_mask) ) { - SHADOW_ERROR("Odd p2m page count c=%#lx t=%"PRtype_info"\n", + SHADOW_ERROR("d%d: Odd p2m page %"PRI_mfn" d=%d c=%lx t=%"PRtype_info"\n", + d->domain_id, mfn_x(page_to_mfn(pg)), + owner ? owner->domain_id : DOMID_INVALID, pg->count_info, pg->u.inuse.type_info); + pg->count_info &= ~PGC_count_mask; + page_set_owner(pg, NULL); } - pg->count_info &= ~PGC_count_mask; pg->u.sh.type = SH_type_p2m_table; /* p2m code reuses type-info */ - page_set_owner(pg, NULL); /* This is called both from the p2m code (which never holds the * paging lock) and the log-dirty code (which always does). */ @@ -3132,7 +3129,9 @@ int shadow_enable(struct domain *d, u32 e = __map_domain_page(pg); write_32bit_pse_identmap(e); unmap_domain_page(e); + pg->count_info = 1; pg->u.inuse.type_info = PGT_l2_page_table | 1 | PGT_validated; + page_set_owner(pg, d); } paging_lock(d); @@ -3170,7 +3169,11 @@ int shadow_enable(struct domain *d, u32 if ( rv != 0 && !pagetable_is_null(p2m_get_pagetable(p2m)) ) p2m_teardown(p2m); if ( rv != 0 && pg != NULL ) + { + pg->count_info &= ~PGC_count_mask; + page_set_owner(pg, NULL); shadow_free_p2m_page(d, pg); + } domain_unpause(d); return rv; } @@ -3279,7 +3282,22 @@ out: /* Must be called outside the lock */ if ( unpaged_pagetable ) + { + if ( page_get_owner(unpaged_pagetable) == d && + (unpaged_pagetable->count_info & PGC_count_mask) == 1 ) + { + unpaged_pagetable->count_info &= ~PGC_count_mask; + page_set_owner(unpaged_pagetable, NULL); + } + /* Complain here in cases where shadow_free_p2m_page() won't. */ + else if ( !page_get_owner(unpaged_pagetable) && + !(unpaged_pagetable->count_info & PGC_count_mask) ) + SHADOW_ERROR("d%d: Odd unpaged pt %"PRI_mfn" c=%lx t=%"PRtype_info"\n", + d->domain_id, mfn_x(page_to_mfn(unpaged_pagetable)), + unpaged_pagetable->count_info, + unpaged_pagetable->u.inuse.type_info); shadow_free_p2m_page(d, unpaged_pagetable); + } } void shadow_final_teardown(struct domain *d)