Add example xen-detect.c code for detecting application execution in

Xen PV or HVM contexts, using the Xen CPUID extensions.
Signed-off-by: Keir Fraser <keir@xensource.com>

1 files changed, 107 insertions, 0 deletions

diff --git a/tools/misc/xen-detect.c b/tools/misc/xen-detect.c
new file mode 100644
index 0000000000..6ac23f4453
--- /dev/null
+++ b/tools/misc/xen-detect.c
@@ -0,0 +1,107 @@
+/******************************************************************************
+ * xen_detect.c
+ * 
+ * Simple GNU C / POSIX application to detect execution on Xen VMM platform.
+ * 
+ * Copyright (c) 2007, XenSource Inc.
+ * 
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+static int pv_context;
+
+static void cpuid(uint32_t idx,
+                  uint32_t *eax,
+                  uint32_t *ebx,
+                  uint32_t *ecx,
+                  uint32_t *edx)
+{
+    asm volatile (
+        "test %1,%1 ; jz 1f ; ud2a ; .ascii \"xen\" ; 1: cpuid"
+        : "=a" (*eax), "=b" (*ebx), "=c" (*ecx), "=d" (*edx)
+        : "0" (idx), "1" (pv_context) );
+}
+
+static int check_for_xen(void)
+{
+    uint32_t eax, ebx, ecx, edx;
+    char signature[13];
+
+    cpuid(0x40000000, &eax, &ebx, &ecx, &edx);
+    *(uint32_t *)(signature + 0) = ebx;
+    *(uint32_t *)(signature + 4) = ecx;
+    *(uint32_t *)(signature + 8) = edx;
+    signature[12] = '\0';
+
+    if ( strcmp("XenVMMXenVMM", signature) || (eax < 0x40000002) )
+        return 0;
+
+    cpuid(0x40000001, &eax, &ebx, &ecx, &edx);
+    printf("Running in %s context on Xen v%d.%d.\n",
+           pv_context ? "PV" : "HVM", (uint16_t)(eax >> 16), (uint16_t)eax);
+    return 1;
+}
+
+int main(void)
+{
+    pid_t pid;
+    int status;
+    uint32_t dummy;
+
+    /* Check for execution in HVM context. */
+    if ( check_for_xen() )
+        return 0;
+
+    /* Now we check for execution in PV context. */
+    pv_context = 1;
+
+    /*
+     * Fork a child to test the paravirtualised CPUID instruction.
+     * If executed outside Xen PV context, the extended opcode will fault.
+     */
+    pid = fork();
+    switch ( pid )
+    {
+    case 0:
+        /* Child: test paravirtualised CPUID opcode and then exit cleanly. */
+        cpuid(0x40000000, &dummy, &dummy, &dummy, &dummy);
+        exit(0);
+    case -1:
+        fprintf(stderr, "Fork failed.\n");
+        return 0;
+    }
+
+    /*
+     * Parent waits for child to terminate and checks for clean exit.
+     * Only if the exit is clean is it safe for us to try the extended CPUID.
+     */
+    waitpid(pid, &status, 0);
+    if ( WIFEXITED(status) && check_for_xen() )
+        return 0;
+
+    printf("Not running on Xen.\n");
+    return 0;
+}