[Xen-devel] [PATCH v3 34/38] arm/p2m: Add HVMOP_altp2m_change_gfn

[Sergej Proskurin <proskurin@xxxxxxxxxxxxx>]

This commit adds the functionality to change mfn mappings for specified
gfn's in altp2m views. This mechanism can be used within the context of
VMI, e.g., to establish stealthy debugging.

Signed-off-by: Sergej Proskurin <proskurin@xxxxxxxxxxxxx>
---
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Julien Grall <julien.grall@xxxxxxx>
---
v3: Moved the altp2m_lock to guard access to d->arch.altp2m_vttbr[idx]
    in altp2m_change_gfn.

    Locked hp2m to prevent hp2m entries from being modified while the
    function "altp2m_change_gfn" is active.

    Removed setting ap2m->mem_access_enabled in "altp2m_change_gfn", as
    we do not need explicitly splitting pages at this point.

    Extended checks allowing to change gfn's in p2m_ram_(rw|ro) memory
    only.

    Moved the funtion "remove_altp2m_entry" out of this commit.
---
 xen/arch/arm/altp2m.c        | 98 ++++++++++++++++++++++++++++++++++++++++++++
 xen/arch/arm/hvm.c           |  7 +++-
 xen/include/asm-arm/altp2m.h |  6 +++
 3 files changed, 110 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/altp2m.c b/xen/arch/arm/altp2m.c
index 2009bad..fa8d526 100644
--- a/xen/arch/arm/altp2m.c
+++ b/xen/arch/arm/altp2m.c
@@ -301,6 +301,104 @@ out:
     return rc;
 }
 
+int altp2m_change_gfn(struct domain *d,
+                      unsigned int idx,
+                      gfn_t old_gfn,
+                      gfn_t new_gfn)
+{
+    struct p2m_domain *hp2m, *ap2m;
+    mfn_t mfn;
+    p2m_access_t p2ma;
+    p2m_type_t p2mt;
+    unsigned int page_order;
+    int rc = -EINVAL;
+
+    hp2m = p2m_get_hostp2m(d);
+    ap2m = d->arch.altp2m_p2m[idx];
+
+    altp2m_lock(d);
+    p2m_read_lock(hp2m);
+
+    if ( idx >= MAX_ALTP2M || d->arch.altp2m_p2m[idx] == NULL )
+        goto out;
+
+    mfn = p2m_lookup_attr(ap2m, old_gfn, &p2mt, NULL, &page_order);
+
+    /* Check whether the page needs to be reset. */
+    if ( gfn_eq(new_gfn, INVALID_GFN) )
+    {
+        /* If mfn is mapped by old_gfn, remove old_gfn from the altp2m table. 
*/
+        if ( !mfn_eq(mfn, INVALID_MFN) )
+        {
+            rc = remove_altp2m_entry(ap2m, old_gfn, mfn, page_order);
+            if ( rc )
+            {
+                rc = -EINVAL;
+                goto out;
+            }
+        }
+
+        rc = 0;
+        goto out;
+    }
+
+    /* Check hostp2m if no valid entry in altp2m present. */
+    if ( mfn_eq(mfn, INVALID_MFN) )
+    {
+        mfn = p2m_lookup_attr(hp2m, old_gfn, &p2mt, &p2ma, &page_order);
+        if ( mfn_eq(mfn, INVALID_MFN) ||
+             /* Allow changing gfn's in p2m_ram_(rw|ro) memory only. */
+             ((p2mt != p2m_ram_rw) && (p2mt != p2m_ram_ro)) )
+        {
+            rc = -EINVAL;
+            goto out;
+        }
+
+        /* If this is a superpage, copy that first. */
+        if ( page_order != THIRD_ORDER )
+        {
+            rc = modify_altp2m_entry(ap2m, old_gfn, mfn, p2mt, p2ma, 
page_order);
+            if ( rc )
+            {
+                rc = -EINVAL;
+                goto out;
+            }
+        }
+    }
+
+    mfn = p2m_lookup_attr(ap2m, new_gfn, &p2mt, &p2ma, &page_order);
+
+    /* If new_gfn is not part of altp2m, get the mapping information from hp2m 
*/
+    if ( mfn_eq(mfn, INVALID_MFN) )
+        mfn = p2m_lookup_attr(hp2m, new_gfn, &p2mt, &p2ma, &page_order);
+
+    if ( mfn_eq(mfn, INVALID_MFN) ||
+         /* Allow changing gfn's in p2m_ram_(rw|ro) memory only. */
+         ((p2mt != p2m_ram_rw) && (p2mt != p2m_ram_ro)) )
+    {
+        rc = -EINVAL;
+        goto out;
+    }
+
+    /* Set mem access attributes - currently supporting only one (4K) page. */
+    page_order = THIRD_ORDER;
+    rc = modify_altp2m_entry(ap2m, old_gfn, mfn, p2mt, p2ma, page_order);
+    if ( rc )
+    {
+        rc = -EINVAL;
+        goto out;
+    }
+
+    rc = 0;
+
+out:
+    p2m_read_unlock(hp2m);
+    altp2m_unlock(d);
+
+    return rc;
+}
+
+
 static void altp2m_vcpu_reset(struct vcpu *v)
 {
     struct altp2mvcpu *av = &altp2m_vcpu(v);
diff --git a/xen/arch/arm/hvm.c b/xen/arch/arm/hvm.c
index df78893..c754ad1 100644
--- a/xen/arch/arm/hvm.c
+++ b/xen/arch/arm/hvm.c
@@ -145,7 +145,12 @@ static int do_altp2m_op(XEN_GUEST_HANDLE_PARAM(void) arg)
         break;
 
     case HVMOP_altp2m_change_gfn:
-        rc = -EOPNOTSUPP;
+        if ( a.u.change_gfn.pad1 || a.u.change_gfn.pad2 )
+            rc = -EINVAL;
+        else
+            rc = altp2m_change_gfn(d, a.u.change_gfn.view,
+                                   _gfn(a.u.change_gfn.old_gfn),
+                                   _gfn(a.u.change_gfn.new_gfn));
         break;
     }
 
diff --git a/xen/include/asm-arm/altp2m.h b/xen/include/asm-arm/altp2m.h
index 8e40c45..8b459bf 100644
--- a/xen/include/asm-arm/altp2m.h
+++ b/xen/include/asm-arm/altp2m.h
@@ -97,4 +97,10 @@ int altp2m_propagate_change(struct domain *d,
                             p2m_type_t p2mt,
                             p2m_access_t p2ma);
 
+/* Change a gfn->mfn mapping */
+int altp2m_change_gfn(struct domain *d,
+                      unsigned int idx,
+                      gfn_t old_gfn,
+                      gfn_t new_gfn);
+
 #endif /* __ASM_ARM_ALTP2M_H */
-- 
2.9.0


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