memory: Optimize gum_memory_write for Linux/Android

gum/backend-linux/gummemory-linux.c

@@ -20,19 +20,26 @@
 
 #if defined (HAVE_I386) && GLIB_SIZEOF_VOID_P == 4
 # define GUM_SYS_PROCESS_VM_READV  347
+# define GUM_SYS_PROCESS_VM_WRITEV 348
 #elif defined (HAVE_I386) && GLIB_SIZEOF_VOID_P == 8
 # define GUM_SYS_PROCESS_VM_READV  310
+# define GUM_SYS_PROCESS_VM_WRITEV 311
 #elif defined (HAVE_ARM)
 # define GUM_SYS_PROCESS_VM_READV  (__NR_SYSCALL_BASE + 376)
+# define GUM_SYS_PROCESS_VM_WRITEV (__NR_SYSCALL_BASE + 377)
 #elif defined (HAVE_ARM64)
 # define GUM_SYS_PROCESS_VM_READV  270
+# define GUM_SYS_PROCESS_VM_WRITEV 271
 #elif defined (HAVE_MIPS)
 # if _MIPS_SIM == _MIPS_SIM_ABI32
 #  define GUM_SYS_PROCESS_VM_READV (__NR_Linux + 345)
+#  define GUM_SYS_PROCESS_VM_WRITEV (__NR_Linux + 346)
 # elif _MIPS_SIM == _MIPS_SIM_ABI64
 #  define GUM_SYS_PROCESS_VM_READV (__NR_Linux + 304)
+#  define GUM_SYS_PROCESS_VM_WRITEV (__NR_Linux + 305)
 # elif _MIPS_SIM == _MIPS_SIM_NABI32
 #  define GUM_SYS_PROCESS_VM_READV (__NR_Linux + 309)
+#  define GUM_SYS_PROCESS_VM_WRITEV (__NR_Linux + 310)
 # else
 #  error Unexpected MIPS ABI
 # endif
@@ -48,6 +55,11 @@ static gssize gum_libc_process_vm_readv (pid_t pid,
     const struct iovec * remote_iov, gulong riovcnt,
     gulong flags);
 
+static gssize gum_libc_process_vm_writev (pid_t pid,
+    const struct iovec * local_iov, gulong liovcnt,
+    const struct iovec * remote_iov, gulong riovcnt,
+    gulong flags);
+
 gboolean
 gum_memory_is_readable (gconstpointer address,
                         gsize len)
@@ -152,11 +164,40 @@ gum_memory_write (gpointer address,
                   gsize len)
 {
   gboolean success = FALSE;
+  static gboolean kernel_feature_likely_enabled = TRUE;
+  gboolean still_pending = TRUE;
+
+  if (kernel_feature_likely_enabled && gum_linux_check_kernel_version (3, 2, 0))
+  {
+    gssize n;
+    struct iovec local_iov = {
+      .iov_base = (void *) bytes,
+      .iov_len = len
+    };
+    struct iovec remote_iov = {
+      .iov_base = address,
+      .iov_len = len
+    };
+
+    n = gum_libc_process_vm_writev (getpid (), &local_iov, 1, &remote_iov, 1, 0);
+    if (n > 0)
+    {
+      success = (n == len);
+    }
 
-  if (gum_memory_is_writable (address, len))
+    if (n == -1 && errno == ENOSYS)
+      kernel_feature_likely_enabled = FALSE;
+    else
+      still_pending = FALSE;
+  }
+
+  if (still_pending)
   {
-    memcpy (address, bytes, len);
-    success = TRUE;
+    if (gum_memory_is_writable (address, len))
+    {
+      memcpy (address, bytes, len);
+      success = TRUE;
+    }
   }
 
   return success;
@@ -320,3 +361,15 @@ gum_libc_process_vm_readv (pid_t pid,
   return syscall (GUM_SYS_PROCESS_VM_READV, pid, local_iov, liovcnt, remote_iov,
       riovcnt, flags);
 }
+
+static gssize
+gum_libc_process_vm_writev (pid_t pid,
+                           const struct iovec * local_iov,
+                           gulong liovcnt,
+                           const struct iovec * remote_iov,
+                           gulong riovcnt,
+                           gulong flags)
+{
+  return syscall (GUM_SYS_PROCESS_VM_WRITEV, pid, local_iov, liovcnt, remote_iov,
+      riovcnt, flags);
+}