Re: port-xen/47057: Xen NetBSD DomU file system trash under Linux Dom0

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

The following reply was made to PR port-xen/47057; it has been noted by GNATS.

From: Manuel Bouyer <bouyer%antioche.eu.org@localhost>
To: Roger Pau =?iso-8859-1?Q?Monn=E9?= <royger%NetBSD.org@localhost>
Cc: Roger Pau =?iso-8859-1?Q?Monn=E9?= <roger.pau%citrix.com@localhost>,
        "gnats-bugs%NetBSD.org@localhost" <gnats-bugs%NetBSD.org@localhost>,
        "port-xen-maintainer%netbsd.org@localhost" 
<port-xen-maintainer%NetBSD.org@localhost>,
        "gnats-admin%netbsd.org@localhost" <gnats-admin%NetBSD.org@localhost>,
        "netbsd-bugs%netbsd.org@localhost" <netbsd-bugs%NetBSD.org@localhost>
Subject: Re: port-xen/47057: Xen NetBSD DomU file system trash under Linux
 Dom0
Date: Sun, 21 Oct 2012 20:31:18 +0200

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 On Sun, Oct 21, 2012 at 08:10:36PM +0200, Roger Pau Monné wrote:
 > On Sun, Oct 21, 2012 at 8:00 PM, Manuel Bouyer 
 > <bouyer%antioche.eu.org@localhost> wrote:
 > > Does linux do this silently, or does it complain when the ring
 > > corruption occurs ?
 > 
 > With the patch attached in the previous post, we will do the same as
 > Linux (reset indexes and printk). I've never seen that happen in
 > Linux, so I'm not sure if there's anything else.
 > 
 > >> Is it possible that someone writes to the machine address
 > >> xen_start_info.store_mfn and is there anyway to check that nobody is
 > >> mapping this ma to another va?
 > >
 > > I've been thinking about checking this, but it's harder to do.
 > > Maybe it's easier to do this check in the hypervisor ?
 > 
 > Will check that, not sure if there's an easy way to this in the hypervisor.
 
 You can also try the attached patch, which should catch a mapping to
 the same store's ma via regular pmap functons. If it's something more
 clever, we'll need a more clever checks ...
 
 -- 
 Manuel Bouyer <bouyer%antioche.eu.org@localhost>
      NetBSD: 26 ans d'experience feront toujours la difference
 --
 
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 Index: x86/x86/pmap.c
 ===================================================================
 RCS file: /cvsroot/src/sys/arch/x86/x86/pmap.c,v
 retrieving revision 1.178
 diff -u -p -u -r1.178 pmap.c
 --- x86/x86/pmap.c     15 Jun 2012 13:53:40 -0000      1.178
 +++ x86/x86/pmap.c     21 Oct 2012 18:26:43 -0000
 @@ -325,6 +325,8 @@ kmutex_t pmaps_lock;
  
  static vaddr_t pmap_maxkvaddr;
  
 +extern void *xenstore_interface;
 +
  /*
   * XXX kludge: dummy locking to make KASSERTs in uvm_page.c comfortable.
   * actual locking is done by pm_lock.
 @@ -994,6 +996,9 @@ pmap_kenter_pa(vaddr_t va, paddr_t pa, v
        } else
  #endif /* DOM0OPS */
                npte = pmap_pa2pte(pa);
 +
 +      if (xenstore_interface != NULL)
 +              KASSERT(npte != (xen_start_info.store_mfn << PAGE_SHIFT));
        npte |= protection_codes[prot] | PG_k | PG_V | pmap_pg_g;
        npte |= pmap_pat_flags(flags);
        opte = pmap_pte_testset(pte, npte); /* zap! */
 @@ -1026,6 +1031,8 @@ pmap_emap_enter(vaddr_t va, paddr_t pa, 
  #endif
                npte = pmap_pa2pte(pa);
  
 +      if (xenstore_interface != NULL)
 +              KASSERT(npte != (xen_start_info.store_mfn << PAGE_SHIFT));
        npte = pmap_pa2pte(pa);
        npte |= protection_codes[prot] | PG_k | PG_V;
        pmap_pte_set(pte, npte);
 @@ -3900,6 +3907,8 @@ pmap_enter_ma(struct pmap *pmap, vaddr_t
        bool wired = (flags & PMAP_WIRED) != 0;
        struct pmap *pmap2;
  
 +      if (xenstore_interface != NULL)
 +              KASSERT(ma != (xen_start_info.store_mfn << PAGE_SHIFT));
        KASSERT(pmap_initialized);
        KASSERT(curlwp->l_md.md_gc_pmap != pmap);
        KASSERT(va < VM_MAX_KERNEL_ADDRESS);
 Index: xen/x86/xen_pmap.c
 ===================================================================
 RCS file: /cvsroot/src/sys/arch/xen/x86/xen_pmap.c,v
 retrieving revision 1.22
 diff -u -p -u -r1.22 xen_pmap.c
 --- xen/x86/xen_pmap.c 24 Jun 2012 18:31:53 -0000      1.22
 +++ xen/x86/xen_pmap.c 21 Oct 2012 18:26:43 -0000
 @@ -174,12 +174,16 @@ void
  pmap_kenter_ma(vaddr_t va, paddr_t ma, vm_prot_t prot, u_int flags)
  {
        pt_entry_t *pte, opte, npte;
 +      extern void *xenstore_interface;
  
        if (va < VM_MIN_KERNEL_ADDRESS)
                pte = vtopte(va);
        else
                pte = kvtopte(va);
  
 +      if (xenstore_interface != NULL)
 +              KASSERT(ma != (xen_start_info.store_mfn << PAGE_SHIFT) ||
 +                  va == (vaddr_t)xenstore_interface);
        npte = ma | ((prot & VM_PROT_WRITE) ? PG_RW : PG_RO) |
             PG_V | PG_k;
        if (flags & PMAP_NOCACHE)
 
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