libxc: x86: ensure that the initial mapping fits into the guest's memory

In particular we need to check that adding 512KB of slack and
rounding up to a 4MB boundary do not overflow the guest's memory
allocation. Otherwise we run off the end of the p2m when building the
guest's initial page tables and populate them with garbage.

Wei noticed this when build tiny (2MB) mini-os domains.

Reported-by: Wei Liu <Wei.Liu2@citrix.com>
Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Committed-by: Ian Campbell <ian.campbell@citrix.com>

diff --git a/tools/libxc/xc_dom_core.c b/tools/libxc/xc_dom_core.c
index 99f90dd45e8583805eb83ff44ac85492f71c9294..c8062d877361ae2578b9200adbe11617580d8fe6 100644 (file)
--- a/tools/libxc/xc_dom_core.c
+++ b/tools/libxc/xc_dom_core.c
@@ -873,7 +873,8 @@ int xc_dom_build_image(struct xc_dom_image *dom)
         goto err;
     if ( dom->arch_hooks->count_pgtables )
     {
-        dom->arch_hooks->count_pgtables(dom);
+        if ( dom->arch_hooks->count_pgtables(dom) != 0 )
+            goto err;
         if ( (dom->pgtables > 0) &&
              (xc_dom_alloc_segment(dom, &dom->pgtables_seg, "page tables", 0,
                                    dom->pgtables * page_size) != 0) )

diff --git a/tools/libxc/xc_dom_x86.c b/tools/libxc/xc_dom_x86.c
index 0cf16877184dae51adc2ed1f92828e5d3aa9c60b..240d7265fa6bde0ebe8959091777db07b9f67971 100644 (file)
--- a/tools/libxc/xc_dom_x86.c
+++ b/tools/libxc/xc_dom_x86.c
@@ -82,6 +82,7 @@ static int count_pgtables(struct xc_dom_image *dom, int pae,
 {
     int pages, extra_pages;
     xen_vaddr_t try_virt_end;
+    xen_pfn_t try_pfn_end;
 
     extra_pages = dom->alloc_bootstack ? 1 : 0;
     extra_pages += dom->extra_pages;
@@ -91,6 +92,17 @@ static int count_pgtables(struct xc_dom_image *dom, int pae,
     {
         try_virt_end = round_up(dom->virt_alloc_end + pages * PAGE_SIZE_X86,
                                 bits_to_mask(22)); /* 4MB alignment */
+
+        try_pfn_end = (try_virt_end - dom->parms.virt_base) >> PAGE_SHIFT_X86;
+
+        if ( try_pfn_end > dom->total_pages )
+        {
+            xc_dom_panic(dom->xch, XC_OUT_OF_MEMORY,
+                         "%s: not enough memory for initial mapping (%#"PRIpfn" > %#"PRIpfn")",
+                         __FUNCTION__, try_pfn_end, dom->total_pages);
+            return -ENOMEM;
+        }
+
         dom->pg_l4 =
             nr_page_tables(dom, dom->parms.virt_base, try_virt_end, l4_bits);
         dom->pg_l3 =