gdb, gdbarch: Enable inferior calls for shadow stack support.

Inferior calls in GDB reset the current PC to the beginning of the function
that is called.  As no call instruction is executed the new return address
needs to be pushed to the shadow stack and the shadow stack pointer needs
to be updated.

This commit adds a new gdbarch method to push an address on the shadow
stack.  The method is used to adapt the function 'call_function_by_hand_dummy'
for inferior call shadow stack support.

Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org>

gdb/gdbarch-gen.c

@@ -262,6 +262,7 @@ struct gdbarch
   gdbarch_read_core_file_mappings_ftype *read_core_file_mappings = default_read_core_file_mappings;
   gdbarch_use_target_description_from_corefile_notes_ftype *use_target_description_from_corefile_notes = default_use_target_description_from_corefile_notes;
   gdbarch_core_parse_exec_context_ftype *core_parse_exec_context = default_core_parse_exec_context;
+  gdbarch_shadow_stack_push_ftype *shadow_stack_push = nullptr;
 };
 
 /* Create a new ``struct gdbarch'' based on information provided by
@@ -535,6 +536,7 @@ verify_gdbarch (struct gdbarch *gdbarch)
   /* Skip verify of read_core_file_mappings, invalid_p == 0.  */
   /* Skip verify of use_target_description_from_corefile_notes, invalid_p == 0.  */
   /* Skip verify of core_parse_exec_context, invalid_p == 0.  */
+  /* Skip verify of shadow_stack_push, has predicate.  */
   if (!log.empty ())
     internal_error (_("verify_gdbarch: the following are invalid ...%s"),
 		    log.c_str ());
@@ -1406,6 +1408,12 @@ gdbarch_dump (struct gdbarch *gdbarch, struct ui_file *file)
   gdb_printf (file,
 	      "gdbarch_dump: core_parse_exec_context = <%s>\n",
 	      host_address_to_string (gdbarch->core_parse_exec_context));
+  gdb_printf (file,
+	      "gdbarch_dump: gdbarch_shadow_stack_push_p() = %d\n",
+	      gdbarch_shadow_stack_push_p (gdbarch));
+  gdb_printf (file,
+	      "gdbarch_dump: shadow_stack_push = <%s>\n",
+	      host_address_to_string (gdbarch->shadow_stack_push));
   if (gdbarch->dump_tdep != NULL)
     gdbarch->dump_tdep (gdbarch, file);
 }
@@ -5551,3 +5559,27 @@ set_gdbarch_core_parse_exec_context (struct gdbarch *gdbarch,
 {
   gdbarch->core_parse_exec_context = core_parse_exec_context;
 }
+
+bool
+gdbarch_shadow_stack_push_p (struct gdbarch *gdbarch)
+{
+  gdb_assert (gdbarch != NULL);
+  return gdbarch->shadow_stack_push != NULL;
+}
+
+void
+gdbarch_shadow_stack_push (struct gdbarch *gdbarch, CORE_ADDR new_addr, regcache *regcache)
+{
+  gdb_assert (gdbarch != NULL);
+  gdb_assert (gdbarch->shadow_stack_push != NULL);
+  if (gdbarch_debug >= 2)
+    gdb_printf (gdb_stdlog, "gdbarch_shadow_stack_push called\n");
+  gdbarch->shadow_stack_push (gdbarch, new_addr, regcache);
+}
+
+void
+set_gdbarch_shadow_stack_push (struct gdbarch *gdbarch,
+			       gdbarch_shadow_stack_push_ftype shadow_stack_push)
+{
+  gdbarch->shadow_stack_push = shadow_stack_push;
+}

gdb/gdbarch-gen.h

@@ -1801,3 +1801,17 @@ extern void set_gdbarch_use_target_description_from_corefile_notes (struct gdbar
 typedef core_file_exec_context (gdbarch_core_parse_exec_context_ftype) (struct gdbarch *gdbarch, bfd *cbfd);
 extern core_file_exec_context gdbarch_core_parse_exec_context (struct gdbarch *gdbarch, bfd *cbfd);
 extern void set_gdbarch_core_parse_exec_context (struct gdbarch *gdbarch, gdbarch_core_parse_exec_context_ftype *core_parse_exec_context);
+
+/* Some targets support special hardware-assisted control-flow protection
+   technologies.  For example, the Intel Control-Flow Enforcement Technology
+   (Intel CET) on x86 provides a shadow stack and indirect branch tracking.
+   To enable inferior calls the function shadow_stack_push has to be provided.
+
+   Push the address NEW_ADDR on the shadow stack and update the shadow stack
+   pointer. */
+
+extern bool gdbarch_shadow_stack_push_p (struct gdbarch *gdbarch);
+
+typedef void (gdbarch_shadow_stack_push_ftype) (struct gdbarch *gdbarch, CORE_ADDR new_addr, regcache *regcache);
+extern void gdbarch_shadow_stack_push (struct gdbarch *gdbarch, CORE_ADDR new_addr, regcache *regcache);
+extern void set_gdbarch_shadow_stack_push (struct gdbarch *gdbarch, gdbarch_shadow_stack_push_ftype *shadow_stack_push);

gdb/gdbarch_components.py

@@ -2848,3 +2848,19 @@ which all assume current_inferior() is the one to read from.
     predefault="default_core_parse_exec_context",
     invalid=False,
 )
+
+Method(
+    comment="""
+Some targets support special hardware-assisted control-flow protection
+technologies.  For example, the Intel Control-Flow Enforcement Technology
+(Intel CET) on x86 provides a shadow stack and indirect branch tracking.
+To enable inferior calls the function shadow_stack_push has to be provided.
+
+Push the address NEW_ADDR on the shadow stack and update the shadow stack
+pointer.
+""",
+    type="void",
+    name="shadow_stack_push",
+    params=[("CORE_ADDR", "new_addr"), ("regcache *", "regcache")],
+    predicate=True,
+)

gdb/infcall.c

@@ -1448,10 +1448,16 @@ call_function_by_hand_dummy (struct value *function,
   /* Create the dummy stack frame.  Pass in the call dummy address as,
      presumably, the ABI code knows where, in the call dummy, the
      return address should be pointed.  */
-  sp = gdbarch_push_dummy_call (gdbarch, function,
-				get_thread_regcache (inferior_thread ()),
-				bp_addr, args.size (), args.data (),
-				sp, return_method, struct_addr);
+  regcache *regcache = get_thread_regcache (inferior_thread ());
+  sp = gdbarch_push_dummy_call (gdbarch, function, regcache, bp_addr,
+				args.size (), args.data (), sp,
+				return_method, struct_addr);
+
+  /* Push the return address of the inferior (bp_addr) on the shadow stack
+     and update the shadow stack pointer.  As we don't execute a call
+     instruction to start the inferior we need to handle this manually.  */
+  if (gdbarch_shadow_stack_push_p (gdbarch))
+    gdbarch_shadow_stack_push (gdbarch, bp_addr, regcache);
 
   /* Set up a frame ID for the dummy frame so we can pass it to
      set_momentary_breakpoint.  We need to give the breakpoint a frame