[XEN PATCH] tools/misc: xen-hvmcrash: Inject #DF instead of overwriting RIP

[Matthew Barnes <matthew.barnes@xxxxxxxxx>]

xen-hvmcrash would previously save records, overwrite the instruction
pointer with a bogus value, and then restore them to crash a domain
just enough to cause the guest OS to memdump.

This approach is found to be unreliable when tested on a guest running
Windows 10 x64, with some executions doing nothing at all.

Another approach would be to trigger NMIs. This approach is found to be
unreliable when tested on Linux (Ubuntu 22.04), as Linux will ignore
NMIs if it is not configured to handle such.

Injecting a double fault abort to all vCPUs is found to be more
reliable at crashing and invoking memdumps from Windows and Linux
domains.

This patch modifies the xen-hvmcrash tool to inject #DF to all vCPUs
belonging to the specified domain, instead of overwriting RIP.

Signed-off-by: Matthew Barnes <matthew.barnes@xxxxxxxxx>
---
 tools/misc/xen-hvmcrash.c | 77 +++++++--------------------------------
 1 file changed, 13 insertions(+), 64 deletions(-)

diff --git a/tools/misc/xen-hvmcrash.c b/tools/misc/xen-hvmcrash.c
index 1d058fa40a47..8ef1beb388f8 100644
--- a/tools/misc/xen-hvmcrash.c
+++ b/tools/misc/xen-hvmcrash.c
@@ -38,22 +38,21 @@
 #include <sys/stat.h>
 #include <arpa/inet.h>
 
+#define XC_WANT_COMPAT_DEVICEMODEL_API
 #include <xenctrl.h>
 #include <xen/xen.h>
 #include <xen/domctl.h>
 #include <xen/hvm/save.h>
 
+#define X86_ABORT_DF 8
+
 int
 main(int argc, char **argv)
 {
     int domid;
     xc_interface *xch;
     xc_domaininfo_t dominfo;
-    int ret;
-    uint32_t len;
-    uint8_t *buf;
-    uint32_t off;
-    struct hvm_save_descriptor *descriptor;
+    int vcpu_id, ret;
 
     if (argc != 2 || !argv[1] || (domid = atoi(argv[1])) < 0) {
         fprintf(stderr, "usage: %s <domid>\n", argv[0]);
@@ -77,66 +76,16 @@ main(int argc, char **argv)
         exit(1);
     }
 
-    ret = xc_domain_pause(xch, domid);
-    if (ret < 0) {
-        perror("xc_domain_pause");
-        exit(-1);
-    }
-
-    /*
-     * Calling with zero buffer length should return the buffer length
-     * required.
-     */
-    ret = xc_domain_hvm_getcontext(xch, domid, 0, 0);
-    if (ret < 0) {
-        perror("xc_domain_hvm_getcontext");
-        exit(1);
-    }
-    
-    len = ret;
-    buf = malloc(len);
-    if (buf == NULL) {
-        perror("malloc");
-        exit(1);
-    }
-
-    ret = xc_domain_hvm_getcontext(xch, domid, buf, len);
-    if (ret < 0) {
-        perror("xc_domain_hvm_getcontext");
-        exit(1);
-    }
-
-    off = 0;
-
-    while (off < len) {
-        descriptor = (struct hvm_save_descriptor *)(buf + off);
-
-        off += sizeof (struct hvm_save_descriptor);
-
-        if (descriptor->typecode == HVM_SAVE_CODE(CPU)) {
-            HVM_SAVE_TYPE(CPU) *cpu;
-
-            /* Overwrite EIP/RIP with some recognisable but bogus value */
-            cpu = (HVM_SAVE_TYPE(CPU) *)(buf + off);
-            printf("CPU[%d]: RIP = %" PRIx64 "\n", descriptor->instance, 
cpu->rip);
-            cpu->rip = 0xf001;
-        } else if (descriptor->typecode == HVM_SAVE_CODE(END)) {
-            break;
+    for (vcpu_id = 0; vcpu_id <= dominfo.max_vcpu_id; vcpu_id++) {
+        printf("Injecting #DF to vcpu ID #%d...\n", vcpu_id);
+        ret = xc_hvm_inject_trap(xch, domid, vcpu_id,
+                                X86_ABORT_DF,
+                                XEN_DMOP_EVENT_hw_exc, 0,
+                                NULL, NULL);
+        if (ret < 0) {
+            fprintf(stderr, "Could not inject #DF to vcpu ID #%d\n", vcpu_id);
+            perror("xc_hvm_inject_trap");
         }
-
-        off += descriptor->length;
-    }
-
-    ret = xc_domain_hvm_setcontext(xch, domid, buf, len);
-    if (ret < 0) {
-        perror("xc_domain_hvm_setcontext");
-        exit(1);
-    }
-
-    ret = xc_domain_unpause(xch, domid);
-    if (ret < 0) {
-        perror("xc_domain_unpause");
-        exit(1);
     }
 
     return 0;
-- 
2.34.1