[Xen-devel] [PATCH for-4.12 V5 2/2] x86/altp2m: fix HVMOP_altp2m_set_domain_state race

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

HVMOP_altp2m_set_domain_state does not domain_pause(), presumably
on purpose (as it was originally supposed to cater to a in-guest
agent, and a domain pausing itself is not a good idea).

This can lead to domain crashes in the vmx_vmexit_handler() code
that checks if the guest has the ability to switch EPTP without an
exit. That code can __vmread() the host p2m's EPT_POINTER
(before HVMOP_altp2m_set_domain_state "for_each_vcpu()" has a
chance to run altp2m_vcpu_initialise(), but after
d->arch.altp2m_active is set).

Signed-off-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>

---
CC: Jan Beulich <jbeulich@xxxxxxxx>
CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: Wei Liu <wei.liu2@xxxxxxxxxx>
CC: "Roger Pau Monné" <roger.pau@xxxxxxxxxx>
---
 xen/arch/x86/hvm/hvm.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 410623d..79c7d81 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -4538,6 +4538,10 @@ static int do_altp2m_op(
             break;
         }
 
+        rc = domain_pause_except_self(d);
+        if ( rc )
+            break;
+
         ostate = d->arch.altp2m_active;
         d->arch.altp2m_active = !!a.u.domain_state.state;
 
@@ -4556,6 +4560,8 @@ static int do_altp2m_op(
             if ( ostate )
                 p2m_flush_altp2m(d);
         }
+
+        domain_unpause_except_self(d);
         break;
     }
 
-- 
2.7.4


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