[PATCH] fbsd nat: Disable address space randomization when requested.

[John Baldwin]

Use procctl(2) with PROC_ASLR_CTL to disable address space
randomization in the current gdb process before forking a child
process for a new inferior when address space randomization is
disabled.

gdb/ChangeLog:

	* configure.ac: Check for <sys/procctl.h>.
	* config.in, configure: Regenerate.
	* fbsd-nat.c: Include <sys/procctl.h> if present.
	[PROC_ASLR_CTL] (maybe_disable_address_space_randomization): New.
	(fbsd_nat_target::create_inferior)
	(fbsd_nat_target::supports_disable_randomization): New.
	* fbsd-nat.h (fbsd_nat_target::create_inferior)
	(fbsd_nat_target::supports_disable_randomization): New.
---
 gdb/ChangeLog    | 11 +++++++
 gdb/config.in    |  3 ++
 gdb/configure    |  2 +-
 gdb/configure.ac |  2 +-
 gdb/fbsd-nat.c   | 74 ++++++++++++++++++++++++++++++++++++++++++++++++
 gdb/fbsd-nat.h   |  5 ++++
 6 files changed, 95 insertions(+), 2 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 799d6a7670..e5497740b1 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,14 @@
+2021-06-12  John Baldwin  <jhb@FreeBSD.org>
+
+	* configure.ac: Check for <sys/procctl.h>.
+	* config.in, configure: Regenerate.
+	* fbsd-nat.c: Include <sys/procctl.h> if present.
+	[PROC_ASLR_CTL] (maybe_disable_address_space_randomization): New.
+	(fbsd_nat_target::create_inferior)
+	(fbsd_nat_target::supports_disable_randomization): New.
+	* fbsd-nat.h (fbsd_nat_target::create_inferior)
+	(fbsd_nat_target::supports_disable_randomization): New.
+
 2021-06-12  John Baldwin  <jhb@FreeBSD.org>
 
 	* remote.c (remote_new_objfile): Fix indentation.
diff --git a/gdb/config.in b/gdb/config.in
index 99c924f9ba..9342604ac4 100644
--- a/gdb/config.in
+++ b/gdb/config.in
@@ -486,6 +486,9 @@
 /* Define to 1 if you have the <sys/poll.h> header file. */
 #undef HAVE_SYS_POLL_H
 
+/* Define to 1 if you have the <sys/procctl.h> header file. */
+#undef HAVE_SYS_PROCCTL_H
+
 /* Define to 1 if you have the <sys/procfs.h> header file. */
 #undef HAVE_SYS_PROCFS_H
 
diff --git a/gdb/configure b/gdb/configure
index 3d3977b26a..c6b5906d9e 100755
--- a/gdb/configure
+++ b/gdb/configure
@@ -12260,7 +12260,7 @@ fi
 for ac_header in nlist.h machine/reg.h \
                   thread_db.h \
 		  sys/file.h sys/filio.h sys/ioctl.h sys/param.h \
-		  sys/resource.h sys/ptrace.h ptrace.h \
+		  sys/procctl.h sys/resource.h sys/ptrace.h ptrace.h \
 		  sys/reg.h sys/debugreg.h \
 		  termios.h elf_hp.h
 do :
diff --git a/gdb/configure.ac b/gdb/configure.ac
index df340ffa82..68cf84d6ca 100644
--- a/gdb/configure.ac
+++ b/gdb/configure.ac
@@ -1298,7 +1298,7 @@ AC_HEADER_STDC
 AC_CHECK_HEADERS([nlist.h machine/reg.h \
                   thread_db.h \
 		  sys/file.h sys/filio.h sys/ioctl.h sys/param.h \
-		  sys/resource.h sys/ptrace.h ptrace.h \
+		  sys/procctl.h sys/resource.h sys/ptrace.h ptrace.h \
 		  sys/reg.h sys/debugreg.h \
 		  termios.h elf_hp.h])
 AC_CHECK_HEADERS(sys/user.h, [], [],
diff --git a/gdb/fbsd-nat.c b/gdb/fbsd-nat.c
index 581c04d5f8..e1e88ed9a2 100644
--- a/gdb/fbsd-nat.c
+++ b/gdb/fbsd-nat.c
@@ -29,6 +29,9 @@
 #include "gdbsupport/gdb_wait.h"
 #include "inf-ptrace.h"
 #include <sys/types.h>
+#ifdef HAVE_SYS_PROCCTL_H
+#include <sys/procctl.h>
+#endif
 #include <sys/procfs.h>
 #include <sys/ptrace.h>
 #include <sys/signal.h>
@@ -1401,6 +1404,67 @@ fbsd_nat_target::supports_stopped_by_sw_breakpoint ()
 }
 #endif
 
+#ifdef PROC_ASLR_CTL
+class maybe_disable_address_space_randomization
+{
+public:
+  maybe_disable_address_space_randomization(bool disable_randomization)
+    : m_aslr_ctl_set (false), m_aslr_ctl(0)
+  {
+    if (disable_randomization)
+      {
+	if (procctl (P_PID, getpid (), PROC_ASLR_STATUS, &m_aslr_ctl) == -1)
+	  {
+	    warning (_("Failed to fetch current address space randomization status: %s"),
+		     safe_strerror (errno));
+	    return;
+	  }
+
+	m_aslr_ctl &= ~PROC_ASLR_ACTIVE;
+	if (m_aslr_ctl == PROC_ASLR_FORCE_DISABLE)
+	  return;
+
+	int ctl = PROC_ASLR_FORCE_DISABLE;
+	if (procctl (P_PID, getpid (), PROC_ASLR_CTL, &ctl) == -1)
+	  {
+	    warning (_("Error disabling address space randomization: %s"),
+		     safe_strerror (errno));
+	    return;
+	  }
+
+	m_aslr_ctl_set = true;
+      }
+  }
+
+  ~maybe_disable_address_space_randomization()
+  {
+    if (m_aslr_ctl_set)
+      {
+	if (procctl (P_PID, getpid (), PROC_ASLR_CTL, &m_aslr_ctl) == -1)
+	  warning (_("Error restoring address space randomization: %s"),
+		   safe_strerror (errno));
+      }
+  }
+
+private:
+  bool m_aslr_ctl_set;
+  int m_aslr_ctl;
+};
+#endif
+
+void
+fbsd_nat_target::create_inferior (const char *exec_file,
+				  const std::string &allargs,
+				  char **env, int from_tty)
+{
+#ifdef PROC_ASLR_CTL
+  maybe_disable_address_space_randomization restore_aslr_ctl
+    (disable_randomization);
+#endif
+
+  inf_ptrace_target::create_inferior (exec_file, allargs, env, from_tty);
+}
+
 #ifdef TDP_RFPPWAIT
 /* Target hook for follow_fork.  On entry and at return inferior_ptid is
    the ptid of the followed inferior.  */
@@ -1526,6 +1590,16 @@ fbsd_nat_target::supports_multi_process ()
   return true;
 }
 
+bool
+fbsd_nat_target::supports_disable_randomization ()
+{
+#ifdef PROC_ASLR_CTL
+  return true;
+#else
+  return false;
+#endif
+}
+
 void _initialize_fbsd_nat ();
 void
 _initialize_fbsd_nat ()
diff --git a/gdb/fbsd-nat.h b/gdb/fbsd-nat.h
index 772655d320..1fdb939935 100644
--- a/gdb/fbsd-nat.h
+++ b/gdb/fbsd-nat.h
@@ -67,6 +67,9 @@ class fbsd_nat_target : public inf_ptrace_target
   thread_control_capabilities get_thread_control_capabilities () override
   { return tc_schedlock; }
 
+  void create_inferior (const char *, const std::string &,
+			char **, int) override;
+
   void resume (ptid_t, int, enum gdb_signal) override;
 
   ptid_t wait (ptid_t, struct target_waitstatus *, target_wait_flags) override;
@@ -98,6 +101,8 @@ class fbsd_nat_target : public inf_ptrace_target
 #endif
 
   bool supports_multi_process () override;
+
+  bool supports_disable_randomization () override;
 };
 
 #endif /* fbsd-nat.h */
-- 
2.31.1