x86/hap: do not switch on log dirty for VRAM tracking

XEN_DMOP_track_dirty_vram possibly calls into paging_log_dirty_enable
when using HAP mode, and it can interact badly with other ongoing
paging domctls, as XEN_DMOP_track_dirty_vram is not holding the domctl
lock.

This was detected as a result of the following assert triggering when
doing repeated migrations of a HAP HVM domain with a stubdom:

Assertion 'd->arch.paging.log_dirty.allocs == 0' failed at paging.c:198
----[ Xen-4.17-unstable  x86_64  debug=y  Not tainted ]----
CPU:    34
RIP:    e008:[<ffff82d040314b3b>] arch/x86/mm/paging.c#paging_free_log_dirty_bitmap+0x606/0x6
RFLAGS: 0000000000010206   CONTEXT: hypervisor (d0v23)
[...]
Xen call trace:
   [<ffff82d040314b3b>] R arch/x86/mm/paging.c#paging_free_log_dirty_bitmap+0x606/0x63a
   [<ffff82d040279f96>] S xsm/flask/hooks.c#domain_has_perm+0x5a/0x67
   [<ffff82d04031577f>] F paging_domctl+0x251/0xd41
   [<ffff82d04031640c>] F paging_domctl_continuation+0x19d/0x202
   [<ffff82d0403202fa>] F pv_hypercall+0x150/0x2a7
   [<ffff82d0403a729d>] F lstar_enter+0x12d/0x140

Such assert triggered because the stubdom used
XEN_DMOP_track_dirty_vram while dom0 was in the middle of executing
XEN_DOMCTL_SHADOW_OP_OFF, and so log dirty become enabled while
retiring the old structures, thus leading to new entries being
populated in already clear slots.

Fix this by not enabling log dirty for VRAM tracking, similar to what
is done when using shadow instead of HAP. Call
p2m_enable_hardware_log_dirty when enabling VRAM tracking in order to
get some hardware assistance if available. As a side effect the memory
pressure on the p2m pool should go down if only VRAM tracking is
enabled, as the dirty bitmap is no longer allocated.

Note that paging_log_dirty_range (used to get the dirty bitmap for
VRAM tracking) doesn't use the log dirty bitmap, and instead relies on
checking whether each gfn on the range has been switched from
p2m_ram_logdirty to p2m_ram_rw in order to account for dirty pages.

This is CVE-2022-26356 / XSA-397.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: 4f4db53784d912c4f409a451c36ebfd4754e0a42
master date: 2022-04-05 14:11:30 +0200

diff --git a/xen/arch/x86/mm/hap/hap.c b/xen/arch/x86/mm/hap/hap.c
index 73575deb0d8a40114958191e4c7d7c9c41453c50..47a7487fa7a3f87560f1b92bc46fec94abd147e2 100644 (file)
--- a/xen/arch/x86/mm/hap/hap.c
+++ b/xen/arch/x86/mm/hap/hap.c
@@ -69,13 +69,6 @@ int hap_track_dirty_vram(struct domain *d,
     {
         unsigned int size = DIV_ROUND_UP(nr_frames, BITS_PER_BYTE);
 
-        if ( !paging_mode_log_dirty(d) )
-        {
-            rc = paging_log_dirty_enable(d, false);
-            if ( rc )
-                goto out;
-        }
-
         rc = -ENOMEM;
         dirty_bitmap = vzalloc(size);
         if ( !dirty_bitmap )
@@ -107,6 +100,10 @@ int hap_track_dirty_vram(struct domain *d,
 
             paging_unlock(d);
 
+            domain_pause(d);
+            p2m_enable_hardware_log_dirty(d);
+            domain_unpause(d);
+
             if ( oend > ostart )
                 p2m_change_type_range(d, ostart, oend,
                                       p2m_ram_logdirty, p2m_ram_rw);

diff --git a/xen/arch/x86/mm/paging.c b/xen/arch/x86/mm/paging.c
index dd6b2bdf6fd6b63f2c67f1fc60e3a8430bf1a377..97ac9ccf590d7cd0aaae5799ef6274b5baa76a81 100644 (file)
--- a/xen/arch/x86/mm/paging.c
+++ b/xen/arch/x86/mm/paging.c
@@ -211,7 +211,7 @@ static int paging_free_log_dirty_bitmap(struct domain *d, int rc)
     return rc;
 }
 
-int paging_log_dirty_enable(struct domain *d, bool log_global)
+static int paging_log_dirty_enable(struct domain *d, bool log_global)
 {
     int ret;
 

diff --git a/xen/include/asm-x86/paging.h b/xen/include/asm-x86/paging.h
index 996c2cd0383f63577c4a6b6edfc762218ea86251..27890791d895dd4040ce7ffd5f4b46ecdfa4bc88 100644 (file)
--- a/xen/include/asm-x86/paging.h
+++ b/xen/include/asm-x86/paging.h
@@ -162,9 +162,6 @@ void paging_log_dirty_range(struct domain *d,
                             unsigned long nr,
                             uint8_t *dirty_bitmap);
 
-/* enable log dirty */
-int paging_log_dirty_enable(struct domain *d, bool log_global);
-
 /* log dirty initialization */
 void paging_log_dirty_init(struct domain *d, const struct log_dirty_ops *ops);