[Xen-devel] [PATCH 2/2] x86/hvm: honor guest's option when updating secondary system time for guest

[Feng Wu <feng.wu@xxxxxxxxx>]

In this patch, we add a new hypervisor which allows guests to enable
SMAP check when Xen is updating the secondary system time for guest.
The SMAP check for this update is disabled by default.

Reported-by: Sander Eikelenboom <linux@xxxxxxxxxxxxxx>
Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
---
 xen/arch/x86/domain.c        |  6 ++++++
 xen/arch/x86/hvm/hvm.c       |  2 ++
 xen/arch/x86/time.c          | 12 +++++++++++-
 xen/include/asm-x86/domain.h |  9 ++++++++-
 xen/include/public/vcpu.h    | 10 ++++++++++
 5 files changed, 37 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index b0c8810..a787c46 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -1053,6 +1053,12 @@ arch_do_vcpu_op(
         break;
     }
 
+    case VCPUOP_enable_smap_check_vcpu_time_memory_area:
+    {
+        v->arch.enable_smap_check = 1;
+        break;
+    }
+
     case VCPUOP_get_physid:
     {
         struct vcpu_get_physid cpu_id;
diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index ef2411c..a922711 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -4629,6 +4629,7 @@ static long hvm_vcpu_op(
     case VCPUOP_stop_singleshot_timer:
     case VCPUOP_register_vcpu_info:
     case VCPUOP_register_vcpu_time_memory_area:
+    case VCPUOP_enable_smap_check_vcpu_time_memory_area:
         rc = do_vcpu_op(cmd, vcpuid, arg);
         break;
     default:
@@ -4688,6 +4689,7 @@ static long hvm_vcpu_op_compat32(
     case VCPUOP_stop_singleshot_timer:
     case VCPUOP_register_vcpu_info:
     case VCPUOP_register_vcpu_time_memory_area:
+    case VCPUOP_enable_smap_check_vcpu_time_memory_area:
         rc = compat_vcpu_op(cmd, vcpuid, arg);
         break;
     default:
diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
index a4e1656..338381e 100644
--- a/xen/arch/x86/time.c
+++ b/xen/arch/x86/time.c
@@ -821,7 +821,7 @@ static void __update_vcpu_system_time(struct vcpu *v, int 
force)
         v->arch.pv_vcpu.pending_system_time = _u;
 }
 
-bool_t update_secondary_system_time(const struct vcpu *v,
+bool_t update_secondary_system_time(struct vcpu *v,
                                     struct vcpu_time_info *u)
 {
     XEN_GUEST_HANDLE(vcpu_time_info_t) user_u = v->arch.time_info_guest;
@@ -829,9 +829,16 @@ bool_t update_secondary_system_time(const struct vcpu *v,
     if ( guest_handle_is_null(user_u) )
         return 1;
 
+    if ( v->arch.enable_smap_check )
+        v->arch.smap_check_policy = SMAP_CHECK_ENABLED;
+
     /* 1. Update userspace version. */
     if ( __copy_field_to_guest(user_u, u, version) == sizeof(u->version) )
+    {
+        if ( v->arch.enable_smap_check )
+            v->arch.smap_check_policy = SMAP_CHECK_HONOR_CPL_AC;
         return 0;
+    }
     wmb();
     /* 2. Update all other userspace fields. */
     __copy_to_guest(user_u, u, 1);
@@ -840,6 +847,9 @@ bool_t update_secondary_system_time(const struct vcpu *v,
     u->version = version_update_end(u->version);
     __copy_field_to_guest(user_u, u, version);
 
+    if ( v->arch.enable_smap_check )
+        v->arch.smap_check_policy = SMAP_CHECK_HONOR_CPL_AC;
+
     return 1;
 }
 
diff --git a/xen/include/asm-x86/domain.h b/xen/include/asm-x86/domain.h
index d7cac4f..051fed0 100644
--- a/xen/include/asm-x86/domain.h
+++ b/xen/include/asm-x86/domain.h
@@ -455,6 +455,13 @@ struct arch_vcpu
      *     SMAP_CHECK_DISABLED     - disable the check
      */
     uint8_t smap_check_policy;
+
+    /*
+     * This is a flag to indicate that whether the guest wants to enable
+     * SMAP check when Xen is updating the secondary system time from it.
+     */
+    bool_t enable_smap_check;
+    uint16_t pad;
 } __cacheline_aligned;
 
 #define SMAP_CHECK_HONOR_CPL_AC  0
@@ -466,7 +473,7 @@ struct arch_vcpu
 #define hvm_svm         hvm_vcpu.u.svm
 
 bool_t update_runstate_area(struct vcpu *);
-bool_t update_secondary_system_time(const struct vcpu *,
+bool_t update_secondary_system_time(struct vcpu *,
                                     struct vcpu_time_info *);
 
 void vcpu_show_execution_state(struct vcpu *);
diff --git a/xen/include/public/vcpu.h b/xen/include/public/vcpu.h
index e888daf..d348395 100644
--- a/xen/include/public/vcpu.h
+++ b/xen/include/public/vcpu.h
@@ -227,6 +227,16 @@ struct vcpu_register_time_memory_area {
 typedef struct vcpu_register_time_memory_area vcpu_register_time_memory_area_t;
 DEFINE_XEN_GUEST_HANDLE(vcpu_register_time_memory_area_t);
 
+/*
+ * Flags to tell Xen whether we need to do the SMAP check when updating
+ * the secondary copy of the vcpu time when SMAP is enabled. Since the
+ * memory location for the secondary copy of the vcpu time may be mapped
+ * into userspace by guests intendedly, we let the guest to determine
+ * whether the check is needed. The default behavior of hypevisor is
+ * not doing the check.
+ */
+#define VCPUOP_enable_smap_check_vcpu_time_memory_area   14
+
 #endif /* __XEN_PUBLIC_VCPU_H__ */
 
 /*
-- 
1.8.3.1


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