gdb, gdbarch: Introduce gdbarch method to get the shadow stack pointer.

This patch is required by the following commit
"gdb: Enable displaced stepping with shadow stack on amd64 linux."

Reviewed-By: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
Approved-By: Luis Machado <luis.machado@arm.com>
Approved-By: Andrew Burgess <aburgess@redhat.com>

diff --git a/gdb/arch-utils.c b/gdb/arch-utils.c
index 96fb2c4836e54cb4fb659d374d4420a34ab26e38..f2af80e70405d27d9efbb67ac79115179ff681a1 100644 (file)
--- a/gdb/arch-utils.c
+++ b/gdb/arch-utils.c
@@ -1218,6 +1218,16 @@ default_gdbarch_return_value
                                readbuf, writebuf);
 }
 
+/* See arch-utils.h.  */
+
+std::optional<CORE_ADDR>
+default_get_shadow_stack_pointer (gdbarch *gdbarch, regcache *regcache,
+                                 bool &shadow_stack_enabled)
+{
+  shadow_stack_enabled = false;
+  return {};
+}
+
 obstack *gdbarch_obstack (gdbarch *arch)
 {
   return &arch->obstack;

diff --git a/gdb/arch-utils.h b/gdb/arch-utils.h
index 1509cb7441e6f41a539327651353a1967b9440ac..14a84b747332b5885dbb201d4eeedc4d24c23e88 100644 (file)
--- a/gdb/arch-utils.h
+++ b/gdb/arch-utils.h
@@ -414,4 +414,9 @@ extern enum return_value_convention default_gdbarch_return_value
       struct regcache *regcache, struct value **read_value,
       const gdb_byte *writebuf);
 
+/* Default implementation of gdbarch default_get_shadow_stack_pointer
+   method.  */
+extern std::optional<CORE_ADDR> default_get_shadow_stack_pointer
+  (gdbarch *gdbarch, regcache *regcache, bool &shadow_stack_enabled);
+
 #endif /* GDB_ARCH_UTILS_H */

diff --git a/gdb/gdbarch-gen.c b/gdb/gdbarch-gen.c
index a77f9b7d26599c832dc9d6110f7a4ef7250c30b0..09bb4804c432917568d2dc38ccb2e44e18cdf0bb 100644 (file)
--- a/gdb/gdbarch-gen.c
+++ b/gdb/gdbarch-gen.c
@@ -262,6 +262,7 @@ struct gdbarch
   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;
+  gdbarch_get_shadow_stack_pointer_ftype *get_shadow_stack_pointer = default_get_shadow_stack_pointer;
 };
 
 /* Create a new ``struct gdbarch'' based on information provided by
@@ -535,6 +536,7 @@ verify_gdbarch (struct gdbarch *gdbarch)
   /* 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.  */
+  /* Skip verify of get_shadow_stack_pointer, invalid_p == 0.  */
   if (!log.empty ())
     internal_error (_("verify_gdbarch: the following are invalid ...%s"),
                    log.c_str ());
@@ -1409,6 +1411,9 @@ gdbarch_dump (struct gdbarch *gdbarch, struct ui_file *file)
   gdb_printf (file,
              "gdbarch_dump: shadow_stack_push = <%s>\n",
              host_address_to_string (gdbarch->shadow_stack_push));
+  gdb_printf (file,
+             "gdbarch_dump: get_shadow_stack_pointer = <%s>\n",
+             host_address_to_string (gdbarch->get_shadow_stack_pointer));
   if (gdbarch->dump_tdep != NULL)
     gdbarch->dump_tdep (gdbarch, file);
 }
@@ -5561,3 +5566,20 @@ set_gdbarch_shadow_stack_push (struct gdbarch *gdbarch,
 {
   gdbarch->shadow_stack_push = shadow_stack_push;
 }
+
+std::optional<CORE_ADDR>
+gdbarch_get_shadow_stack_pointer (struct gdbarch *gdbarch, regcache *regcache, bool &shadow_stack_enabled)
+{
+  gdb_assert (gdbarch != NULL);
+  gdb_assert (gdbarch->get_shadow_stack_pointer != NULL);
+  if (gdbarch_debug >= 2)
+    gdb_printf (gdb_stdlog, "gdbarch_get_shadow_stack_pointer called\n");
+  return gdbarch->get_shadow_stack_pointer (gdbarch, regcache, shadow_stack_enabled);
+}
+
+void
+set_gdbarch_get_shadow_stack_pointer (struct gdbarch *gdbarch,
+                                     gdbarch_get_shadow_stack_pointer_ftype get_shadow_stack_pointer)
+{
+  gdbarch->get_shadow_stack_pointer = get_shadow_stack_pointer;
+}

diff --git a/gdb/gdbarch-gen.h b/gdb/gdbarch-gen.h
index 701e9f099b1eb7848ac270f7b77c0fd04b5a55eb..7171c42fb63e7ee035091fc9961deb2a4f80407e 100644 (file)
--- a/gdb/gdbarch-gen.h
+++ b/gdb/gdbarch-gen.h
@@ -1794,7 +1794,8 @@ extern void set_gdbarch_core_parse_exec_context (struct gdbarch *gdbarch, gdbarc
    technologies.  For example, the Intel Control-Flow Enforcement Technology
    (Intel CET) on x86 provides a shadow stack and indirect branch tracking.
    To enable shadow stack support for inferior calls the shadow_stack_push
-   gdbarch hook has to be provided.
+   gdbarch hook has to be provided.  The get_shadow_stack_pointer gdbarch
+   hook has to be provided to enable displaced stepping.
 
    Push NEW_ADDR to the shadow stack and update the shadow stack pointer. */
 
@@ -1803,3 +1804,16 @@ 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);
+
+/* If possible, return the shadow stack pointer.  If the shadow stack
+   feature is enabled then set SHADOW_STACK_ENABLED to true, otherwise
+   set SHADOW_STACK_ENABLED to false.  This hook has to be provided to enable
+   displaced stepping for shadow stack enabled programs.
+   On some architectures, the shadow stack pointer is available even if the
+   feature is disabled.  So dependent on the target, an implementation of
+   this function may return a valid shadow stack pointer, but set
+   SHADOW_STACK_ENABLED to false. */
+
+typedef std::optional<CORE_ADDR> (gdbarch_get_shadow_stack_pointer_ftype) (struct gdbarch *gdbarch, regcache *regcache, bool &shadow_stack_enabled);
+extern std::optional<CORE_ADDR> gdbarch_get_shadow_stack_pointer (struct gdbarch *gdbarch, regcache *regcache, bool &shadow_stack_enabled);
+extern void set_gdbarch_get_shadow_stack_pointer (struct gdbarch *gdbarch, gdbarch_get_shadow_stack_pointer_ftype *get_shadow_stack_pointer);

diff --git a/gdb/gdbarch_components.py b/gdb/gdbarch_components.py
index 3ae79e44c1e357c07b364656512f7cf959d6749b..f933a09c0fa64d05dca5bdebac0f889a87add0f2 100644 (file)
--- a/gdb/gdbarch_components.py
+++ b/gdb/gdbarch_components.py
@@ -2838,7 +2838,8 @@ 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 shadow stack support for inferior calls the shadow_stack_push
-gdbarch hook has to be provided.
+gdbarch hook has to be provided.  The get_shadow_stack_pointer gdbarch
+hook has to be provided to enable displaced stepping.
 
 Push NEW_ADDR to the shadow stack and update the shadow stack pointer.
 """,
@@ -2847,3 +2848,21 @@ Push NEW_ADDR to the shadow stack and update the shadow stack pointer.
     params=[("CORE_ADDR", "new_addr"), ("regcache *", "regcache")],
     predicate=True,
 )
+
+Method(
+    comment="""
+If possible, return the shadow stack pointer.  If the shadow stack
+feature is enabled then set SHADOW_STACK_ENABLED to true, otherwise
+set SHADOW_STACK_ENABLED to false.  This hook has to be provided to enable
+displaced stepping for shadow stack enabled programs.
+On some architectures, the shadow stack pointer is available even if the
+feature is disabled.  So dependent on the target, an implementation of
+this function may return a valid shadow stack pointer, but set
+SHADOW_STACK_ENABLED to false.
+""",
+    type="std::optional<CORE_ADDR>",
+    name="get_shadow_stack_pointer",
+    params=[("regcache *", "regcache"), ("bool &", "shadow_stack_enabled")],
+    predefault="default_get_shadow_stack_pointer",
+    invalid=False,
+)