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

[patchbot@xxxxxxx]

commit e42e4d8c3e2c391e8ce990e0a2c76d6e9a17aad6
Author:     Matthew Barnes <matthew.barnes@xxxxxxxxx>
AuthorDate: Fri Jul 5 16:05:07 2024 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Mon Jul 22 10:50:03 2024 +0100

    tools/misc: xen-hvmcrash: Inject #DF instead of overwriting RIP
    
    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>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 tools/misc/Makefile       |  2 +-
 tools/misc/xen-hvmcrash.c | 87 +++++++++++++----------------------------------
 2 files changed, 24 insertions(+), 65 deletions(-)

diff --git a/tools/misc/Makefile b/tools/misc/Makefile
index 66d0d6b090..c26e544e83 100644
--- a/tools/misc/Makefile
+++ b/tools/misc/Makefile
@@ -81,7 +81,7 @@ xen-hvmctx: xen-hvmctx.o
        $(CC) $(LDFLAGS) -o $@ $< $(LDLIBS_libxenctrl) $(APPEND_LDFLAGS)
 
 xen-hvmcrash: xen-hvmcrash.o
-       $(CC) $(LDFLAGS) -o $@ $< $(LDLIBS_libxenctrl) $(APPEND_LDFLAGS)
+       $(CC) $(LDFLAGS) -o $@ $< $(LDLIBS_libxenctrl) 
$(LDLIBS_libxendevicemodel) $(APPEND_LDFLAGS)
 
 xen-memshare: xen-memshare.o
        $(CC) $(LDFLAGS) -o $@ $< $(LDLIBS_libxenctrl) $(APPEND_LDFLAGS)
diff --git a/tools/misc/xen-hvmcrash.c b/tools/misc/xen-hvmcrash.c
index 1d058fa40a..5ae5bedb2b 100644
--- a/tools/misc/xen-hvmcrash.c
+++ b/tools/misc/xen-hvmcrash.c
@@ -1,7 +1,7 @@
 /* 
  * xen-hvmcrash.c
  *
- * Attempt to crash an HVM guest by overwriting RIP/EIP with a bogus value
+ * Attempt to crash an HVM guest by injecting #DF to every vcpu
  * 
  * Copyright (c) 2010 Citrix Systems, Inc.
  *
@@ -24,36 +24,25 @@
  * DEALINGS IN THE SOFTWARE.
  */
 
-#include <inttypes.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <stddef.h>
-#include <stdint.h>
-#include <unistd.h>
 #include <string.h>
 #include <errno.h>
-#include <limits.h>
-
-#include <sys/types.h>
-#include <sys/stat.h>
-#include <arpa/inet.h>
 
 #include <xenctrl.h>
-#include <xen/xen.h>
-#include <xen/domctl.h>
-#include <xen/hvm/save.h>
+#include <xendevicemodel.h>
+
+#include <xen/asm/x86-defns.h>
 
 int
 main(int argc, char **argv)
 {
     int domid;
     xc_interface *xch;
+    xendevicemodel_handle *dmod;
     xc_domaininfo_t dominfo;
-    int ret;
-    uint32_t len;
-    uint8_t *buf;
-    uint32_t off;
-    struct hvm_save_descriptor *descriptor;
+    int vcpu_id, ret;
+    bool injected = false;
 
     if (argc != 2 || !argv[1] || (domid = atoi(argv[1])) < 0) {
         fprintf(stderr, "usage: %s <domid>\n", argv[0]);
@@ -83,59 +72,29 @@ main(int argc, char **argv)
         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;
+    dmod = xc_interface_dmod_handle(xch);
+
+    for (vcpu_id = 0; vcpu_id <= dominfo.max_vcpu_id; vcpu_id++) {
+        printf("Injecting #DF to vcpu ID #%d...\n", vcpu_id);
+        ret = xendevicemodel_inject_event(dmod, domid, vcpu_id,
+                                X86_EXC_DF,
+                                XEN_DMOP_EVENT_hw_exc, 0, 0, 0);
+        if (ret < 0) {
+            fprintf(stderr, "Could not inject #DF to vcpu ID #%d: %s\n",
+                    vcpu_id, strerror(errno));
+            continue;
         }
-
-        off += descriptor->length;
+        injected = true;
     }
 
-    ret = xc_domain_hvm_setcontext(xch, domid, buf, len);
+    ret = xc_domain_unpause(xch, domid);
     if (ret < 0) {
-        perror("xc_domain_hvm_setcontext");
+        perror("xc_domain_unpause");
         exit(1);
     }
 
-    ret = xc_domain_unpause(xch, domid);
-    if (ret < 0) {
-        perror("xc_domain_unpause");
+    if (!injected) {
+        fprintf(stderr, "Could not inject #DF to any vcpu!\n");
         exit(1);
     }
 
--
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