plugins: add plugin API to read guest memory

Signed-off-by: Rowan Hart <rowanbhart@gmail.com>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Message-Id: <20240827215329.248434-2-rowanbhart@gmail.com>
[AJB: tweaked cpu_memory_rw_debug call]
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20240916085400.1046925-17-alex.bennee@linaro.org>

include/qemu/qemu-plugin.h

@@ -57,11 +57,19 @@ typedef uint64_t qemu_plugin_id_t;
  * - Remove qemu_plugin_register_vcpu_{tb, insn, mem}_exec_inline.
  *   Those functions are replaced by *_per_vcpu variants, which guarantee
  *   thread-safety for operations.
+ *
+ * version 3:
+ * - modified arguments and return value of qemu_plugin_insn_data to copy
+ *   the data into a user-provided buffer instead of returning a pointer
+ *   to the data.
+ *
+ * version 4:
+ * - added qemu_plugin_read_memory_vaddr
  */
 
 extern QEMU_PLUGIN_EXPORT int qemu_plugin_version;
 
-#define QEMU_PLUGIN_VERSION 3
+#define QEMU_PLUGIN_VERSION 4
 
 /**
  * struct qemu_info_t - system information for plugins
@@ -884,6 +892,28 @@ typedef struct {
 QEMU_PLUGIN_API
 GArray *qemu_plugin_get_registers(void);
 
+/**
+ * qemu_plugin_read_memory_vaddr() - read from memory using a virtual address
+ *
+ * @addr: A virtual address to read from
+ * @data: A byte array to store data into
+ * @len: The number of bytes to read, starting from @addr
+ *
+ * @len bytes of data is read starting at @addr and stored into @data. If @data
+ * is not large enough to hold @len bytes, it will be expanded to the necessary
+ * size, reallocating if necessary. @len must be greater than 0.
+ *
+ * This function does not ensure writes are flushed prior to reading, so
+ * callers should take care when calling this function in plugin callbacks to
+ * avoid attempting to read data which may not yet be written and should use
+ * the memory callback API instead.
+ *
+ * Returns true on success and false on failure.
+ */
+QEMU_PLUGIN_API
+bool qemu_plugin_read_memory_vaddr(uint64_t addr,
+                                   GByteArray *data, size_t len);
+
 /**
  * qemu_plugin_read_register() - read register for current vCPU
  *

plugins/api.c

@@ -560,6 +560,26 @@ GArray *qemu_plugin_get_registers(void)
     return create_register_handles(regs);
 }
 
+bool qemu_plugin_read_memory_vaddr(vaddr addr, GByteArray *data, size_t len)
+{
+    g_assert(current_cpu);
+
+    if (len == 0) {
+        return false;
+    }
+
+    g_byte_array_set_size(data, len);
+
+    int result = cpu_memory_rw_debug(current_cpu, addr, data->data,
+                                     data->len, false);
+
+    if (result < 0) {
+        return false;
+    }
+
+    return true;
+}
+
 int qemu_plugin_read_register(struct qemu_plugin_register *reg, GByteArray *buf)
 {
     g_assert(current_cpu);

plugins/qemu-plugins.symbols

@@ -21,6 +21,7 @@
   qemu_plugin_num_vcpus;
   qemu_plugin_outs;
   qemu_plugin_path_to_binary;
+  qemu_plugin_read_memory_vaddr;
   qemu_plugin_read_register;
   qemu_plugin_register_atexit_cb;
   qemu_plugin_register_flush_cb;