x86/vm_event: add HVM debug exception vm_events

Since in-guest debug exceptions are now unconditionally trapped to Xen, adding
a hook for vm_event subscribers to tap into this new always-on guest event. We
rename along the way hvm_event_breakpoint_type to hvm_event_type to better
match the various events that can be passed with it. We also introduce the
necessary monitor_op domctl's to enable subscribing to the events.

This patch also provides monitor subscribers to int3 events proper access
to the instruction length necessary for accurate event-reinjection. Without
this subscribers manually have to evaluate if the int3 instruction has any
prefix attached which would change the instruction length.

Signed-off-by: Tamas K Lengyel <tamas@tklengyel.com>
Acked-by: Razvan Cojocaru <rcojocaru@bitdefender.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>

tools/libxc/include/xenctrl.h

@@ -2165,7 +2165,8 @@ int xc_monitor_software_breakpoint(xc_interface *xch, domid_t domain_id,
                                    bool enable);
 int xc_monitor_guest_request(xc_interface *xch, domid_t domain_id,
                              bool enable, bool sync);
-
+int xc_monitor_debug_exceptions(xc_interface *xch, domid_t domain_id,
+                                bool enable, bool sync);
 /**
  * This function enables / disables emulation for each REP for a
  * REP-compatible instruction.

tools/libxc/xc_monitor.c

@@ -156,3 +156,28 @@ int xc_monitor_emulate_each_rep(xc_interface *xch, domid_t domain_id,
 
     return do_domctl(xch, &domctl);
 }
+
+int xc_monitor_debug_exceptions(xc_interface *xch, domid_t domain_id,
+                                bool enable, bool sync)
+{
+    DECLARE_DOMCTL;
+
+    domctl.cmd = XEN_DOMCTL_monitor_op;
+    domctl.domain = domain_id;
+    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_DEBUG_EXCEPTION;
+    domctl.u.monitor_op.u.debug_exception.sync = sync;
+
+    return do_domctl(xch, &domctl);
+}
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * tab-width: 4
+ * indent-tabs-mode: nil
+ * End:
+ */

tools/tests/xen-access/xen-access.c

@@ -53,6 +53,10 @@
 #define ERROR(a, b...) fprintf(stderr, a "\n", ## b)
 #define PERROR(a, b...) fprintf(stderr, a ": %s\n", ## b, strerror(errno))
 
+/* From xen/include/asm-x86/processor.h */
+#define X86_TRAP_DEBUG  1
+#define X86_TRAP_INT3   3
+
 typedef struct vm_event {
     domid_t domain_id;
     xenevtchn_handle *xce_handle;
@@ -333,7 +337,7 @@ void usage(char* progname)
 {
     fprintf(stderr, "Usage: %s [-m] <domain_id> write|exec", progname);
 #if defined(__i386__) || defined(__x86_64__)
-            fprintf(stderr, "|breakpoint|altp2m_write|altp2m_exec");
+            fprintf(stderr, "|breakpoint|altp2m_write|altp2m_exec|debug");
 #endif
             fprintf(stderr,
             "\n"
@@ -354,10 +358,12 @@ int main(int argc, char *argv[])
     xc_interface *xch;
     xenmem_access_t default_access = XENMEM_access_rwx;
     xenmem_access_t after_first_access = XENMEM_access_rwx;
+    int memaccess = 0;
     int required = 0;
     int breakpoint = 0;
     int shutting_down = 0;
     int altp2m = 0;
+    int debug = 0;
     uint16_t altp2m_view_id = 0;
 
     char* progname = argv[0];
@@ -391,11 +397,13 @@ int main(int argc, char *argv[])
     {
         default_access = XENMEM_access_rx;
         after_first_access = XENMEM_access_rwx;
+        memaccess = 1;
     }
     else if ( !strcmp(argv[0], "exec") )
     {
         default_access = XENMEM_access_rw;
         after_first_access = XENMEM_access_rwx;
+        memaccess = 1;
     }
 #if defined(__i386__) || defined(__x86_64__)
     else if ( !strcmp(argv[0], "breakpoint") )
@@ -406,11 +414,17 @@ int main(int argc, char *argv[])
     {
         default_access = XENMEM_access_rx;
         altp2m = 1;
+        memaccess = 1;
     }
     else if ( !strcmp(argv[0], "altp2m_exec") )
     {
         default_access = XENMEM_access_rw;
         altp2m = 1;
+        memaccess = 1;
+    }
+    else if ( !strcmp(argv[0], "debug") )
+    {
+        debug = 1;
     }
 #endif
     else
@@ -446,7 +460,7 @@ int main(int argc, char *argv[])
     }
 
     /* With altp2m we just create a new, restricted view of the memory */
-    if ( altp2m )
+    if ( memaccess && altp2m )
     {
         xen_pfn_t gfn = 0;
         unsigned long perm_set = 0;
@@ -493,7 +507,7 @@ int main(int argc, char *argv[])
         }
     }
 
-    if ( !altp2m )
+    if ( memaccess && !altp2m )
     {
         /* Set the default access type and convert all pages to it */
         rc = xc_set_mem_access(xch, domain_id, default_access, ~0ull, 0);
@@ -524,6 +538,16 @@ int main(int argc, char *argv[])
         }
     }
 
+    if ( debug )
+    {
+        rc = xc_monitor_debug_exceptions(xch, domain_id, 1, 1);
+        if ( rc < 0 )
+        {
+            ERROR("Error %d setting debug exception listener with vm_event\n", rc);
+            goto exit;
+        }
+    }
+
     /* Wait for access */
     for (;;)
     {
@@ -534,6 +558,8 @@ int main(int argc, char *argv[])
 
             if ( breakpoint )
                 rc = xc_monitor_software_breakpoint(xch, domain_id, 0);
+            if ( debug )
+                rc = xc_monitor_debug_exceptions(xch, domain_id, 0, 0);
 
             if ( altp2m )
             {
@@ -641,16 +667,16 @@ int main(int argc, char *argv[])
                        req.vcpu_id);
 
                 /* Reinject */
-                rc = xc_hvm_inject_trap(
-                    xch, domain_id, req.vcpu_id, 3,
-                    HVMOP_TRAP_sw_exc, -1, 0, 0);
+                rc = xc_hvm_inject_trap(xch, domain_id, req.vcpu_id,
+                                        X86_TRAP_INT3,
+                                        req.u.software_breakpoint.type, -1,
+                                        req.u.software_breakpoint.insn_length, 0);
                 if (rc < 0)
                 {
                     ERROR("Error %d injecting breakpoint\n", rc);
                     interrupted = -1;
                     continue;
                 }
-
                 break;
             case VM_EVENT_REASON_SINGLESTEP:
                 printf("Singlestep: rip=%016"PRIx64", vcpu %d, altp2m %u\n",
@@ -668,6 +694,27 @@ int main(int argc, char *argv[])
 
                 rsp.flags |= VM_EVENT_FLAG_TOGGLE_SINGLESTEP;
 
+                break;
+            case VM_EVENT_REASON_DEBUG_EXCEPTION:
+                printf("Debug exception: rip=%016"PRIx64", vcpu %d. Type: %u. Length: %u\n",
+                       req.data.regs.x86.rip,
+                       req.vcpu_id,
+                       req.u.debug_exception.type,
+                       req.u.debug_exception.insn_length);
+
+                /* Reinject */
+                rc = xc_hvm_inject_trap(xch, domain_id, req.vcpu_id,
+                                        X86_TRAP_DEBUG,
+                                        req.u.debug_exception.type, -1,
+                                        req.u.debug_exception.insn_length,
+                                        req.data.regs.x86.cr2);
+                if (rc < 0)
+                {
+                    ERROR("Error %d injecting breakpoint\n", rc);
+                    interrupted = -1;
+                    continue;
+                }
+
                 break;
             default:
                 fprintf(stderr, "UNKNOWN REASON CODE %d\n", req.reason);

xen/arch/x86/hvm/monitor.c

@@ -87,12 +87,13 @@ static inline unsigned long gfn_of_rip(unsigned long rip)
     return paging_gva_to_gfn(curr, sreg.base + rip, &pfec);
 }
 
-int hvm_monitor_breakpoint(unsigned long rip,
-                           enum hvm_monitor_breakpoint_type type)
+int hvm_monitor_debug(unsigned long rip, enum hvm_monitor_debug_type type,
+                      unsigned long trap_type, unsigned long insn_length)
 {
     struct vcpu *curr = current;
     struct arch_domain *ad = &curr->domain->arch;
     vm_event_request_t req = {};
+    bool_t sync;
 
     switch ( type )
     {
@@ -101,6 +102,9 @@ int hvm_monitor_breakpoint(unsigned long rip,
             return 0;
         req.reason = VM_EVENT_REASON_SOFTWARE_BREAKPOINT;
         req.u.software_breakpoint.gfn = gfn_of_rip(rip);
+        req.u.software_breakpoint.type = trap_type;
+        req.u.software_breakpoint.insn_length = insn_length;
+        sync = 1;
         break;
 
     case HVM_MONITOR_SINGLESTEP_BREAKPOINT:
@@ -108,6 +112,17 @@ int hvm_monitor_breakpoint(unsigned long rip,
             return 0;
         req.reason = VM_EVENT_REASON_SINGLESTEP;
         req.u.singlestep.gfn = gfn_of_rip(rip);
+        sync = 1;
+        break;
+
+    case HVM_MONITOR_DEBUG_EXCEPTION:
+        if ( !ad->monitor.debug_exception_enabled )
+            return 0;
+        req.reason = VM_EVENT_REASON_DEBUG_EXCEPTION;
+        req.u.debug_exception.gfn = gfn_of_rip(rip);
+        req.u.debug_exception.type = trap_type;
+        req.u.debug_exception.insn_length = insn_length;
+        sync = !!ad->monitor.debug_exception_sync;
         break;
 
     default:
@@ -116,7 +131,7 @@ int hvm_monitor_breakpoint(unsigned long rip,
 
     req.vcpu_id = curr->vcpu_id;
 
-    return vm_event_monitor_traps(curr, 1, &req);
+    return vm_event_monitor_traps(curr, sync, &req);
 }
 
 /*

xen/arch/x86/hvm/vmx/vmx.c

@@ -3376,7 +3376,29 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs)
             HVMTRACE_1D(TRAP_DEBUG, exit_qualification);
             write_debugreg(6, exit_qualification | DR_STATUS_RESERVED_ONE);
             if ( !v->domain->debugger_attached )
-                vmx_propagate_intr(intr_info);
+            {
+                unsigned long insn_len = 0;
+                int rc;
+                unsigned long trap_type = MASK_EXTR(intr_info,
+                                                    INTR_INFO_INTR_TYPE_MASK);
+
+                if ( trap_type >= X86_EVENTTYPE_SW_INTERRUPT )
+                    __vmread(VM_EXIT_INSTRUCTION_LEN, &insn_len);
+
+                rc = hvm_monitor_debug(regs->eip,
+                                       HVM_MONITOR_DEBUG_EXCEPTION,
+                                       trap_type, insn_len);
+
+                /*
+                 * rc < 0 error in monitor/vm_event, crash
+                 * !rc    continue normally
+                 * rc > 0 paused waiting for response, work here is done
+                 */
+                if ( rc < 0 )
+                    goto exit_and_crash;
+                if ( !rc )
+                    vmx_propagate_intr(intr_info);
+            }
             else
                 domain_pause_for_debugger();
             break;
@@ -3391,9 +3413,14 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs)
                 break;
             }
             else {
-                int rc =
-                      hvm_monitor_breakpoint(regs->eip,
-                                             HVM_MONITOR_SOFTWARE_BREAKPOINT);
+                unsigned long insn_len;
+                int rc;
+
+                __vmread(VM_EXIT_INSTRUCTION_LEN, &insn_len);
+                rc = hvm_monitor_debug(regs->eip,
+                                       HVM_MONITOR_SOFTWARE_BREAKPOINT,
+                                       X86_EVENTTYPE_SW_EXCEPTION,
+                                       insn_len);
 
                 if ( !rc )
                 {
@@ -3401,11 +3428,8 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs)
                         .vector = TRAP_int3,
                         .type = X86_EVENTTYPE_SW_EXCEPTION,
                         .error_code = HVM_DELIVER_NO_ERROR_CODE,
+                        .insn_len = insn_len
                     };
-                    unsigned long insn_len;
-
-                    __vmread(VM_EXIT_INSTRUCTION_LEN, &insn_len);
-                    trap.insn_len = insn_len;
                     hvm_inject_trap(&trap);
                     break;
                 }
@@ -3720,8 +3744,10 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs)
         vmx_update_cpu_exec_control(v);
         if ( v->arch.hvm_vcpu.single_step )
         {
-            hvm_monitor_breakpoint(regs->eip,
-                                   HVM_MONITOR_SINGLESTEP_BREAKPOINT);
+            hvm_monitor_debug(regs->eip,
+                              HVM_MONITOR_SINGLESTEP_BREAKPOINT,
+                              0, 0);
+
             if ( v->domain->debugger_attached )
                 domain_pause_for_debugger();
         }

xen/arch/x86/monitor.c

@@ -224,6 +224,22 @@ int arch_monitor_domctl_event(struct domain *d,
         break;
     }
 
+    case XEN_DOMCTL_MONITOR_EVENT_DEBUG_EXCEPTION:
+    {
+        bool_t old_status = ad->monitor.debug_exception_enabled;
+
+        if ( unlikely(old_status == requested_status) )
+            return -EEXIST;
+
+        domain_pause(d);
+        ad->monitor.debug_exception_enabled = requested_status;
+        ad->monitor.debug_exception_sync = requested_status ?
+                                            mop->u.debug_exception.sync :
+                                            0;
+        domain_unpause(d);
+        break;
+    }
+
     default:
         /*
          * Should not be reached unless arch_monitor_get_capabilities() is

xen/include/asm-x86/domain.h

@@ -403,6 +403,8 @@ struct arch_domain
         unsigned int write_ctrlreg_onchangeonly  : 4;
         unsigned int singlestep_enabled          : 1;
         unsigned int software_breakpoint_enabled : 1;
+        unsigned int debug_exception_enabled     : 1;
+        unsigned int debug_exception_sync        : 1;
         struct monitor_msr_bitmap *msr_bitmap;
     } monitor;
 

xen/include/asm-x86/hvm/monitor.h

@@ -23,10 +23,11 @@
 #include <xen/paging.h>
 #include <public/vm_event.h>
 
-enum hvm_monitor_breakpoint_type
+enum hvm_monitor_debug_type
 {
     HVM_MONITOR_SOFTWARE_BREAKPOINT,
     HVM_MONITOR_SINGLESTEP_BREAKPOINT,
+    HVM_MONITOR_DEBUG_EXCEPTION,
 };
 
 /*
@@ -39,8 +40,8 @@ bool_t hvm_monitor_cr(unsigned int index, unsigned long value,
 #define hvm_monitor_crX(cr, new, old) \
                         hvm_monitor_cr(VM_EVENT_X86_##cr, new, old)
 void hvm_monitor_msr(unsigned int msr, uint64_t value);
-int hvm_monitor_breakpoint(unsigned long rip,
-                           enum hvm_monitor_breakpoint_type type);
+int hvm_monitor_debug(unsigned long rip, enum hvm_monitor_debug_type type,
+                      unsigned long trap_type, unsigned long insn_length);
 
 #endif /* __ASM_X86_HVM_MONITOR_H__ */
 

xen/include/asm-x86/monitor.h

@@ -77,7 +77,8 @@ static inline uint32_t arch_monitor_get_capabilities(struct domain *d)
     capabilities = (1U << XEN_DOMCTL_MONITOR_EVENT_WRITE_CTRLREG) |
                    (1U << XEN_DOMCTL_MONITOR_EVENT_MOV_TO_MSR) |
                    (1U << XEN_DOMCTL_MONITOR_EVENT_SOFTWARE_BREAKPOINT) |
-                   (1U << XEN_DOMCTL_MONITOR_EVENT_GUEST_REQUEST);
+                   (1U << XEN_DOMCTL_MONITOR_EVENT_GUEST_REQUEST) |
+                   (1U << XEN_DOMCTL_MONITOR_EVENT_DEBUG_EXCEPTION);
 
     /* Since we know this is on VMX, we can just call the hvm func */
     if ( hvm_is_singlestep_supported() )

xen/include/public/domctl.h

@@ -1080,6 +1080,7 @@ DEFINE_XEN_GUEST_HANDLE(xen_domctl_psr_cmt_op_t);
 #define XEN_DOMCTL_MONITOR_EVENT_SINGLESTEP            2
 #define XEN_DOMCTL_MONITOR_EVENT_SOFTWARE_BREAKPOINT   3
 #define XEN_DOMCTL_MONITOR_EVENT_GUEST_REQUEST         4
+#define XEN_DOMCTL_MONITOR_EVENT_DEBUG_EXCEPTION       5
 
 struct xen_domctl_monitor_op {
     uint32_t op; /* XEN_DOMCTL_MONITOR_OP_* */
@@ -1114,6 +1115,11 @@ struct xen_domctl_monitor_op {
             /* Pause vCPU until response */
             uint8_t sync;
         } guest_request;
+
+        struct {
+            /* Pause vCPU until response */
+            uint8_t sync;
+        } debug_exception;
     } u;
 };
 typedef struct xen_domctl_monitor_op xen_domctl_monitor_op_t;

xen/include/public/vm_event.h

@@ -29,7 +29,7 @@
 
 #include "xen.h"
 
-#define VM_EVENT_INTERFACE_VERSION 0x00000001
+#define VM_EVENT_INTERFACE_VERSION 0x00000002
 
 #if defined(__XEN__) || defined(__XEN_TOOLS__)
 
@@ -119,6 +119,8 @@
 #define VM_EVENT_REASON_SINGLESTEP              7
 /* An event has been requested via HVMOP_guest_request_vm_event. */
 #define VM_EVENT_REASON_GUEST_REQUEST           8
+/* A debug exception was caught */
+#define VM_EVENT_REASON_DEBUG_EXCEPTION         9
 
 /* Supported values for the vm_event_write_ctrlreg index. */
 #define VM_EVENT_X86_CR0    0
@@ -203,8 +205,15 @@ struct vm_event_write_ctrlreg {
     uint64_t old_value;
 };
 
+struct vm_event_singlestep {
+    uint64_t gfn;
+};
+
 struct vm_event_debug {
     uint64_t gfn;
+    uint32_t insn_length;
+    uint8_t type;        /* HVMOP_TRAP_* */
+    uint8_t _pad[3];
 };
 
 struct vm_event_mov_to_msr {
@@ -247,8 +256,9 @@ typedef struct vm_event_st {
         struct vm_event_mem_access            mem_access;
         struct vm_event_write_ctrlreg         write_ctrlreg;
         struct vm_event_mov_to_msr            mov_to_msr;
+        struct vm_event_singlestep            singlestep;
         struct vm_event_debug                 software_breakpoint;
-        struct vm_event_debug                 singlestep;
+        struct vm_event_debug                 debug_exception;
     } u;
 
     union {