[Xen-devel] [PATCH V2] libxc: x86: ensure that the initial mapping fits into the guest's memory

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2013-01-07 at 11:39 +0000, Ian Campbell wrote:
> I shall respin the complete patch shortly.
8<----------------------------------

# HG changeset patch
# User Ian Campbell <ijc@xxxxxxxxxxxxxx>
# Date 1357565755 0
# Node ID c95c8ea2424b928be44550f29119f5e58f628f8b
# Parent  7a61269a0c1ab33cc93b47f88d760f0d1f88eaab
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@xxxxxxxxxx>
Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v2: Correctly account for virt_base, thanks Jan. Now tested with 32 and 
    64 bit pvops kernels.

diff -r 7a61269a0c1a -r c95c8ea2424b tools/libxc/xc_dom_core.c
--- a/tools/libxc/xc_dom_core.c Thu Jan 03 16:31:44 2013 +0000
+++ b/tools/libxc/xc_dom_core.c Mon Jan 07 13:35:55 2013 +0000
@@ -873,7 +873,8 @@ int xc_dom_build_image(struct xc_dom_ima
         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 -r 7a61269a0c1a -r c95c8ea2424b tools/libxc/xc_dom_x86.c
--- a/tools/libxc/xc_dom_x86.c  Thu Jan 03 16:31:44 2013 +0000
+++ b/tools/libxc/xc_dom_x86.c  Mon Jan 07 13:35:55 2013 +0000
@@ -82,6 +82,7 @@ static int count_pgtables(struct xc_dom_
 {
     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_
     {
         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 =



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