[PATCH V2] vm_event: Allow subscribing to write events for specific MSR-s

[Razvan Cojocaru <rcojocaru@bitdefender.com>]

Previously, subscribing to MSR write events was an all-or-none
approach, with special cases for introspection MSR-s. This patch
allows the vm_event consumer to specify exactly what MSR-s it is
interested in, and as a side-effect gets rid of the
vmx_introspection_force_enabled_msrs[] special case.
This replaces the previously posted "xen: Filter out MSR write
events" patch.

Signed-off-by: Razvan Cojocaru <rcojocaru@bitdefender.com>

---
Changes since V1:
 - Removed ARM stubs.
 - Corrected domain_unpause(d) omission.
 - Moved enable / disable and query functions from vm_event.c to
   monitor.c.
---
 tools/libxc/include/xenctrl.h      |  4 +-
 tools/libxc/xc_monitor.c           |  6 +--
 xen/arch/x86/hvm/event.c           |  3 +-
 xen/arch/x86/hvm/hvm.c             |  3 +-
 xen/arch/x86/hvm/vmx/vmcs.c        | 26 ++-----------
 xen/arch/x86/hvm/vmx/vmx.c         | 10 ++---
 xen/arch/x86/monitor.c             | 79 ++++++++++++++++++++++++++++++++------
 xen/arch/x86/vm_event.c            | 10 +++++
 xen/include/asm-x86/domain.h       |  4 +-
 xen/include/asm-x86/hvm/hvm.h      |  8 ++--
 xen/include/asm-x86/hvm/vmx/vmcs.h |  7 ----
 xen/include/asm-x86/monitor.h      |  2 +
 xen/include/public/domctl.h        |  3 +-
 13 files changed, 99 insertions(+), 66 deletions(-)

diff --git a/tools/libxc/include/xenctrl.h b/tools/libxc/include/xenctrl.h
index f5a034a..9698d46 100644
--- a/tools/libxc/include/xenctrl.h
+++ b/tools/libxc/include/xenctrl.h
@@ -2183,8 +2183,8 @@ int xc_monitor_get_capabilities(xc_interface *xch, domid_t domain_id,
 int xc_monitor_write_ctrlreg(xc_interface *xch, domid_t domain_id,
                              uint16_t index, bool enable, bool sync,
                              bool onchangeonly);
-int xc_monitor_mov_to_msr(xc_interface *xch, domid_t domain_id, bool enable,
-                          bool extended_capture);
+int xc_monitor_mov_to_msr(xc_interface *xch, domid_t domain_id, uint32_t msr,
+                          bool enable);
 int xc_monitor_singlestep(xc_interface *xch, domid_t domain_id, bool enable);
 int xc_monitor_software_breakpoint(xc_interface *xch, domid_t domain_id,
                                    bool enable);
diff --git a/tools/libxc/xc_monitor.c b/tools/libxc/xc_monitor.c
index b1705dd..78131b2 100644
--- a/tools/libxc/xc_monitor.c
+++ b/tools/libxc/xc_monitor.c
@@ -86,8 +86,8 @@ int xc_monitor_write_ctrlreg(xc_interface *xch, domid_t domain_id,
     return do_domctl(xch, &domctl);
 }
 
-int xc_monitor_mov_to_msr(xc_interface *xch, domid_t domain_id, bool enable,
-                          bool extended_capture)
+int xc_monitor_mov_to_msr(xc_interface *xch, domid_t domain_id, uint32_t msr,
+                          bool enable)
 {
     DECLARE_DOMCTL;
 
@@ -96,7 +96,7 @@ int xc_monitor_mov_to_msr(xc_interface *xch, domid_t domain_id, bool enable,
     domctl.u.monitor_op.op = enable ? XEN_DOMCTL_MONITOR_OP_ENABLE
                                     : XEN_DOMCTL_MONITOR_OP_DISABLE;
     domctl.u.monitor_op.event = XEN_DOMCTL_MONITOR_EVENT_MOV_TO_MSR;
-    domctl.u.monitor_op.u.mov_to_msr.extended_capture = extended_capture;
+    domctl.u.monitor_op.u.mov_to_msr.msr = msr;
 
     return do_domctl(xch, &domctl);
 }
diff --git a/xen/arch/x86/hvm/event.c b/xen/arch/x86/hvm/event.c
index 56c5514..015910b 100644
--- a/xen/arch/x86/hvm/event.c
+++ b/xen/arch/x86/hvm/event.c
@@ -57,9 +57,8 @@ bool_t hvm_event_cr(unsigned int index, unsigned long value, unsigned long old)
 void hvm_event_msr(unsigned int msr, uint64_t value)
 {
     struct vcpu *curr = current;
-    struct arch_domain *ad = &curr->domain->arch;
 
-    if ( ad->monitor.mov_to_msr_enabled )
+    if ( arch_monitor_is_msr_enabled(curr->domain, msr) )
     {
         vm_event_request_t req = {
             .reason = VM_EVENT_REASON_MOV_TO_MSR,
diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index f24126d..7c2a98c 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -3695,7 +3695,6 @@ int hvm_msr_write_intercept(unsigned int msr, uint64_t msr_content,
     bool_t mtrr;
     unsigned int edx, index;
     int ret = X86EMUL_OKAY;
-    struct arch_domain *currad = &current->domain->arch;
 
     HVMTRACE_3D(MSR_WRITE, msr,
                (uint32_t)msr_content, (uint32_t)(msr_content >> 32));
@@ -3703,7 +3702,7 @@ int hvm_msr_write_intercept(unsigned int msr, uint64_t msr_content,
     hvm_cpuid(1, NULL, NULL, NULL, &edx);
     mtrr = !!(edx & cpufeat_mask(X86_FEATURE_MTRR));
 
-    if ( may_defer && unlikely(currad->monitor.mov_to_msr_enabled) )
+    if ( may_defer && unlikely(arch_monitor_is_msr_enabled(v->domain, msr)) )
     {
         ASSERT(v->arch.vm_event);
 
diff --git a/xen/arch/x86/hvm/vmx/vmcs.c b/xen/arch/x86/hvm/vmx/vmcs.c
index 8284281..f92f4b8 100644
--- a/xen/arch/x86/hvm/vmx/vmcs.c
+++ b/xen/arch/x86/hvm/vmx/vmcs.c
@@ -37,6 +37,7 @@
 #include <asm/hvm/vmx/vvmx.h>
 #include <asm/hvm/vmx/vmcs.h>
 #include <asm/flushtlb.h>
+#include <asm/monitor.h>
 #include <asm/shadow.h>
 #include <asm/tboot.h>
 #include <asm/apic.h>
@@ -108,18 +109,6 @@ u64 vmx_ept_vpid_cap __read_mostly;
 u64 vmx_vmfunc __read_mostly;
 bool_t vmx_virt_exception __read_mostly;
 
-const u32 vmx_introspection_force_enabled_msrs[] = {
-    MSR_IA32_SYSENTER_EIP,
-    MSR_IA32_SYSENTER_ESP,
-    MSR_IA32_SYSENTER_CS,
-    MSR_IA32_MC0_CTL,
-    MSR_STAR,
-    MSR_LSTAR
-};
-
-const unsigned int vmx_introspection_force_enabled_msrs_size =
-    ARRAY_SIZE(vmx_introspection_force_enabled_msrs);
-
 static DEFINE_PER_CPU_READ_MOSTLY(paddr_t, vmxon_region);
 static DEFINE_PER_CPU(paddr_t, current_vmcs);
 static DEFINE_PER_CPU(struct list_head, active_vmcs_list);
@@ -810,17 +799,8 @@ void vmx_disable_intercept_for_msr(struct vcpu *v, u32 msr, int type)
     if ( msr_bitmap == NULL )
         return;
 
-    if ( unlikely(d->arch.monitor.mov_to_msr_enabled &&
-                  d->arch.monitor.mov_to_msr_extended) &&
-         vm_event_check_ring(&d->vm_event->monitor) )
-    {
-        unsigned int i;
-
-        /* Filter out MSR-s needed for memory introspection */
-        for ( i = 0; i < vmx_introspection_force_enabled_msrs_size; i++ )
-            if ( msr == vmx_introspection_force_enabled_msrs[i] )
-                return;
-    }
+    if ( unlikely(arch_monitor_is_msr_enabled(d, msr)) )
+        return;
 
     /*
      * See Intel PRM Vol. 3, 20.6.9 (MSR-Bitmap Address). Early manuals
diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index bc4410f..9135441 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -1958,16 +1958,12 @@ void vmx_hypervisor_cpuid_leaf(uint32_t sub_idx,
         *eax |= XEN_HVM_CPUID_X2APIC_VIRT;
 }
 
-static void vmx_enable_msr_exit_interception(struct domain *d)
+static void vmx_enable_msr_interception(struct domain *d, uint32_t msr)
 {
     struct vcpu *v;
-    unsigned int i;
 
-    /* Enable interception for MSRs needed for memory introspection. */
     for_each_vcpu ( d, v )
-        for ( i = 0; i < vmx_introspection_force_enabled_msrs_size; i++ )
-            vmx_enable_intercept_for_msr(v, vmx_introspection_force_enabled_msrs[i],
-                                         MSR_TYPE_W);
+        vmx_enable_intercept_for_msr(v, msr, MSR_TYPE_W);
 }
 
 static bool_t vmx_is_singlestep_supported(void)
@@ -2166,7 +2162,7 @@ static struct hvm_function_table __initdata vmx_function_table = {
     .handle_eoi           = vmx_handle_eoi,
     .nhvm_hap_walk_L1_p2m = nvmx_hap_walk_L1_p2m,
     .hypervisor_cpuid_leaf = vmx_hypervisor_cpuid_leaf,
-    .enable_msr_exit_interception = vmx_enable_msr_exit_interception,
+    .enable_msr_interception = vmx_enable_msr_interception,
     .is_singlestep_supported = vmx_is_singlestep_supported,
     .set_mode = vmx_set_mode,
     .altp2m_vcpu_update_p2m = vmx_vcpu_update_eptp,
diff --git a/xen/arch/x86/monitor.c b/xen/arch/x86/monitor.c
index 1fec412..4c96968 100644
--- a/xen/arch/x86/monitor.c
+++ b/xen/arch/x86/monitor.c
@@ -22,6 +22,58 @@
 #include <asm/monitor.h>
 #include <public/vm_event.h>
 
+static int arch_monitor_enable_msr(struct domain *d, u32 msr)
+{
+    if ( !d->arch.monitor_msr_bitmap )
+        return -EINVAL;
+
+    if ( msr <= 0x1fff )
+        set_bit(msr, d->arch.monitor_msr_bitmap + 0x000/BYTES_PER_LONG);
+    else if ( (msr >= 0xc0000000) && (msr <= 0xc0001fff) )
+    {
+        msr &= 0x1fff;
+        set_bit(msr, d->arch.monitor_msr_bitmap + 0x400/BYTES_PER_LONG);
+    }
+
+    hvm_enable_msr_interception(d, msr);
+
+    return 0;
+}
+
+static int arch_monitor_disable_msr(struct domain *d, u32 msr)
+{
+    if ( !d->arch.monitor_msr_bitmap )
+        return -EINVAL;
+
+    if ( msr <= 0x1fff )
+        clear_bit(msr, d->arch.monitor_msr_bitmap + 0x000/BYTES_PER_LONG);
+    else if ( (msr >= 0xc0000000) && (msr <= 0xc0001fff) )
+    {
+        msr &= 0x1fff;
+        clear_bit(msr, d->arch.monitor_msr_bitmap + 0x400/BYTES_PER_LONG);
+    }
+
+    return 0;
+}
+
+bool_t arch_monitor_is_msr_enabled(const struct domain *d, u32 msr)
+{
+    bool_t rc = 0;
+
+    if ( !d->arch.monitor_msr_bitmap )
+        return 0;
+
+    if ( msr <= 0x1fff )
+        rc = test_bit(msr, d->arch.monitor_msr_bitmap + 0x000/BYTES_PER_LONG);
+    else if ( (msr >= 0xc0000000) && (msr <= 0xc0001fff) )
+    {
+        msr &= 0x1fff;
+        rc = test_bit(msr, d->arch.monitor_msr_bitmap + 0x400/BYTES_PER_LONG);
+    }
+
+    return rc;
+}
+
 int arch_monitor_domctl_event(struct domain *d,
                               struct xen_domctl_monitor_op *mop)
 {
@@ -77,25 +129,28 @@ int arch_monitor_domctl_event(struct domain *d,
 
     case XEN_DOMCTL_MONITOR_EVENT_MOV_TO_MSR:
     {
-        bool_t old_status = ad->monitor.mov_to_msr_enabled;
+        bool_t old_status;
+        int rc;
+        u32 msr = mop->u.mov_to_msr.msr;
 
-        if ( unlikely(old_status == requested_status) )
-            return -EEXIST;
+        domain_pause(d);
 
-        if ( requested_status && mop->u.mov_to_msr.extended_capture &&
-             !hvm_enable_msr_exit_interception(d) )
-            return -EOPNOTSUPP;
+        old_status = arch_monitor_is_msr_enabled(d, msr);
 
-        domain_pause(d);
+        if ( unlikely(old_status == requested_status) )
+        {
+            domain_unpause(d);
+            return -EEXIST;
+        }
 
-        if ( requested_status && mop->u.mov_to_msr.extended_capture )
-            ad->monitor.mov_to_msr_extended = 1;
+        if ( requested_status )
+            rc = arch_monitor_enable_msr(d, msr);
         else
-            ad->monitor.mov_to_msr_extended = 0;
+            rc = arch_monitor_disable_msr(d, msr);
 
-        ad->monitor.mov_to_msr_enabled = requested_status;
         domain_unpause(d);
-        break;
+
+        return rc;
     }
 
     case XEN_DOMCTL_MONITOR_EVENT_SINGLESTEP:
diff --git a/xen/arch/x86/vm_event.c b/xen/arch/x86/vm_event.c
index 5635603..9b4267e 100644
--- a/xen/arch/x86/vm_event.c
+++ b/xen/arch/x86/vm_event.c
@@ -27,6 +27,13 @@ int vm_event_init_domain(struct domain *d)
 {
     struct vcpu *v;
 
+    d->arch.monitor_msr_bitmap = alloc_xenheap_page();
+
+    if ( !d->arch.monitor_msr_bitmap )
+        return -ENOMEM;
+
+    memset(d->arch.monitor_msr_bitmap, 0, PAGE_SIZE);
+
     for_each_vcpu ( d, v )
     {
         if ( v->arch.vm_event )
@@ -55,6 +62,9 @@ void vm_event_cleanup_domain(struct domain *d)
         v->arch.vm_event = NULL;
     }
 
+    free_xenheap_page(d->arch.monitor_msr_bitmap);
+    d->arch.monitor_msr_bitmap = NULL;
+
     d->arch.mem_access_emulate_each_rep = 0;
     memset(&d->arch.monitor, 0, sizeof(d->arch.monitor));
     memset(&d->monitor, 0, sizeof(d->monitor));
diff --git a/xen/include/asm-x86/domain.h b/xen/include/asm-x86/domain.h
index d393ed2..d8d91c2 100644
--- a/xen/include/asm-x86/domain.h
+++ b/xen/include/asm-x86/domain.h
@@ -398,12 +398,12 @@ struct arch_domain
         unsigned int write_ctrlreg_enabled       : 4;
         unsigned int write_ctrlreg_sync          : 4;
         unsigned int write_ctrlreg_onchangeonly  : 4;
-        unsigned int mov_to_msr_enabled          : 1;
-        unsigned int mov_to_msr_extended         : 1;
         unsigned int singlestep_enabled          : 1;
         unsigned int software_breakpoint_enabled : 1;
     } monitor;
 
+    unsigned long *monitor_msr_bitmap;
+
     /* Mem_access emulation control */
     bool_t mem_access_emulate_each_rep;
 
diff --git a/xen/include/asm-x86/hvm/hvm.h b/xen/include/asm-x86/hvm/hvm.h
index 7b7ff3f..9d1c0ef 100644
--- a/xen/include/asm-x86/hvm/hvm.h
+++ b/xen/include/asm-x86/hvm/hvm.h
@@ -211,7 +211,7 @@ struct hvm_function_table {
                                   uint32_t *eax, uint32_t *ebx,
                                   uint32_t *ecx, uint32_t *edx);
 
-    void (*enable_msr_exit_interception)(struct domain *d);
+    void (*enable_msr_interception)(struct domain *d, uint32_t msr);
     bool_t (*is_singlestep_supported)(void);
     int (*set_mode)(struct vcpu *v, int mode);
 
@@ -565,11 +565,11 @@ static inline enum hvm_intblk nhvm_interrupt_blocked(struct vcpu *v)
     return hvm_funcs.nhvm_intr_blocked(v);
 }
 
-static inline bool_t hvm_enable_msr_exit_interception(struct domain *d)
+static inline bool_t hvm_enable_msr_interception(struct domain *d, uint32_t msr)
 {
-    if ( hvm_funcs.enable_msr_exit_interception )
+    if ( hvm_funcs.enable_msr_interception )
     {
-        hvm_funcs.enable_msr_exit_interception(d);
+        hvm_funcs.enable_msr_interception(d, msr);
         return 1;
     }
 
diff --git a/xen/include/asm-x86/hvm/vmx/vmcs.h b/xen/include/asm-x86/hvm/vmx/vmcs.h
index b54f52f..7bf5326 100644
--- a/xen/include/asm-x86/hvm/vmx/vmcs.h
+++ b/xen/include/asm-x86/hvm/vmx/vmcs.h
@@ -562,13 +562,6 @@ enum vmcs_field {
     HOST_RIP                        = 0x00006c16,
 };
 
-/*
- * A set of MSR-s that need to be enabled for memory introspection
- * to work.
- */
-extern const u32 vmx_introspection_force_enabled_msrs[];
-extern const unsigned int vmx_introspection_force_enabled_msrs_size;
-
 #define VMCS_VPID_WIDTH 16
 
 #define MSR_TYPE_R 1
diff --git a/xen/include/asm-x86/monitor.h b/xen/include/asm-x86/monitor.h
index 0954b59..74e5b1b 100644
--- a/xen/include/asm-x86/monitor.h
+++ b/xen/include/asm-x86/monitor.h
@@ -50,4 +50,6 @@ int arch_monitor_domctl_op(struct domain *d, struct xen_domctl_monitor_op *mop)
 int arch_monitor_domctl_event(struct domain *d,
                               struct xen_domctl_monitor_op *mop);
 
+bool_t arch_monitor_is_msr_enabled(const struct domain *d, u32 msr);
+
 #endif /* __ASM_X86_MONITOR_H__ */
diff --git a/xen/include/public/domctl.h b/xen/include/public/domctl.h
index 2457698..875c09a 100644
--- a/xen/include/public/domctl.h
+++ b/xen/include/public/domctl.h
@@ -1107,8 +1107,7 @@ struct xen_domctl_monitor_op {
         } mov_to_cr;
 
         struct {
-            /* Enable the capture of an extended set of MSRs */
-            uint8_t extended_capture;
+            uint32_t msr;
         } mov_to_msr;
 
         struct {
-- 
1.9.1


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