Patchwork [v2,PR,gdb/21870] aarch64: Leftover uncleared debug registers

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Submitter Weimin Pan
Date July 3, 2018, 12:07 a.m.
Message ID <1530576444-24656-1-git-send-email-weimin.pan@oracle.com>
Download mbox | patch
Permalink /patch/28206/
State New
Headers show

Comments

Weimin Pan - July 3, 2018, 12:07 a.m.
At issue here is that ptrace() does not validate either address or size 
when setting a hardware watchpoint/breakpoint. As a result, watchpoints 
were set at address 0, the initial value of aarch64_debug_reg_state in 
aarch64_process_info, and DR_CONTROL_LENGTH (dreg_state.dbg_regs[i].ctrl) 
got changed to a non-zero default value, when the PTRACE_SETREGSET request 
was made in aarch64_linux_set_debug_regs(), in preparation for resuming 
the thread.

I sent out a patch upstream for review last year. Yao Qi commented that
he needed to take a look at ptrace implementation to better understand
why this was happening. Unfortunately he didn't get a chance to do so.

This is a revised patch which calls ptrace only if any debug register
has changed, either address or control containing a non-zero value,
in aarch64_linux_set_debug_regs() and is similar to what x86 does - 
x86_linux_update_debug_registers() checks if a debug register has 
non-zero reference count before setting it.

Tested on aarch64-linux-gnu. No regressions.
---
 gdb/ChangeLog                                     |   6 +
 gdb/nat/aarch64-linux-hw-point.c                  |   7 +
 gdb/testsuite/ChangeLog                           |  20 ++-
 gdb/testsuite/gdb.arch/aarch64-dbreg-contents.c   | 179 ++++++++++++++++++++++
 gdb/testsuite/gdb.arch/aarch64-dbreg-contents.exp |  40 +++++
 5 files changed, 244 insertions(+), 8 deletions(-)
 create mode 100644 gdb/testsuite/gdb.arch/aarch64-dbreg-contents.c
 create mode 100644 gdb/testsuite/gdb.arch/aarch64-dbreg-contents.exp

Patch

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 7b108bf..d5bf15f 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,9 @@ 
+2018-06-27  Weimin Pan  <weimin.pan@oracle.com>
+
+	PR gdb/21870
+	* nat/aarch64-linux-hw-point.c (aarch64_linux_set_debug_regs):
+	Validate debug register contents before calling ptrace.
+
 2018-06-18  Tom Tromey  <tom@tromey.com>
 
 	* solib-aix.c (solib_aix_get_section_offsets): Return
diff --git a/gdb/nat/aarch64-linux-hw-point.c b/gdb/nat/aarch64-linux-hw-point.c
index a3931ea..41ac304 100644
--- a/gdb/nat/aarch64-linux-hw-point.c
+++ b/gdb/nat/aarch64-linux-hw-point.c
@@ -694,11 +694,18 @@  aarch64_linux_set_debug_regs (struct aarch64_debug_reg_state *state,
   iov.iov_len = (offsetof (struct user_hwdebug_state, dbg_regs)
 		 + count * sizeof (regs.dbg_regs[0]));
 
+  int changed_regs = 0;
   for (i = 0; i < count; i++)
     {
       regs.dbg_regs[i].addr = addr[i];
       regs.dbg_regs[i].ctrl = ctrl[i];
+      /* Check to see if any of these debug registers contains valid data,
+         e.g. non-zero, before calling ptrace.  See PR gdb/21870.  */
+      if (ctrl[i] || addr[i])
+        changed_regs++;
     }
+  if (changed_regs == 0)
+    return;
 
   if (ptrace (PTRACE_SETREGSET, tid,
 	      watchpoint ? NT_ARM_HW_WATCH : NT_ARM_HW_BREAK,
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index a812061..0ce2d34 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,4 +1,9 @@ 
+2018-06-27  Weimin Pan  <weimin.pan@oracle.com>
+
+	PR gdb/21870
+	* gdb.arch/aarch64-dbreg-contents.c: New file.
+	* gdb.arch/aarch64-dbreg-contents.exp: New file.
+
 2018-06-18  Tom de Vries  <tdevries@suse.de>
 
 	* gdb.ada/bp_inlined_func.exp: Allow 5 breakpoint locations.
 
diff --git a/gdb/testsuite/gdb.arch/aarch64-dbreg-contents.c b/gdb/testsuite/gdb.arch/aarch64-dbreg-contents.c
new file mode 100644
index 0000000..85d4a03
--- /dev/null
+++ b/gdb/testsuite/gdb.arch/aarch64-dbreg-contents.c
@@ -0,0 +1,179 @@ 
+/* Test case for setting a memory-write unaligned watchpoint on aarch64.
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely.  */
+
+#define _GNU_SOURCE 1
+#ifdef __ia64__
+#define ia64_fpreg ia64_fpreg_DISABLE
+#define pt_all_user_regs pt_all_user_regs_DISABLE
+#endif  /* __ia64__ */
+#include <sys/ptrace.h>
+#ifdef __ia64__
+#undef ia64_fpreg
+#undef pt_all_user_regs
+#endif  /* __ia64__ */
+#include <linux/ptrace.h>
+#include <sys/types.h>
+#include <sys/user.h>
+#if defined __i386__ || defined __x86_64__
+#include <sys/debugreg.h>
+#endif
+
+#include <assert.h>
+#include <unistd.h>
+#include <sys/wait.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <stddef.h>
+#include <errno.h>
+#include <sys/uio.h>
+#include <elf.h>
+#include <error.h>
+
+static __attribute__((unused)) pid_t child;
+
+static __attribute__((unused)) void
+cleanup (void)
+{
+  if (child > 0)
+    kill (child, SIGKILL);
+  child = 0;
+}
+
+static __attribute__((unused)) void
+handler_fail (int signo)
+{
+  cleanup ();
+  signal (signo, SIG_DFL);
+  raise (signo);
+}
+
+#ifdef __aarch64__
+
+#define SET_WATCHPOINT set_watchpoint
+
+/* Macros to extract fields from the hardware debug information word.  */
+#define AARCH64_DEBUG_NUM_SLOTS(x) ((x) & 0xff)
+#define AARCH64_DEBUG_ARCH(x) (((x) >> 8) & 0xff)
+/* Macro for the expected version of the ARMv8-A debug architecture.  */
+#define AARCH64_DEBUG_ARCH_V8 0x6
+#define DR_CONTROL_ENABLED(ctrl)        (((ctrl) & 0x1) == 1)
+#define DR_CONTROL_LENGTH(ctrl)         (((ctrl) >> 5) & 0xff)
+
+static void
+set_watchpoint (pid_t pid, volatile void *addr, unsigned len_mask)
+{
+  struct user_hwdebug_state dreg_state;
+  struct iovec iov;
+  long l;
+
+  assert (len_mask >= 0x01);
+  assert (len_mask <= 0xff);
+
+  iov.iov_base = &dreg_state;
+  iov.iov_len = sizeof (dreg_state);
+  errno = 0;
+  l = ptrace (PTRACE_GETREGSET, pid, NT_ARM_HW_WATCH, &iov);
+  assert (l == 0);
+  assert (AARCH64_DEBUG_ARCH (dreg_state.dbg_info) == AARCH64_DEBUG_ARCH_V8);
+  assert (AARCH64_DEBUG_NUM_SLOTS (dreg_state.dbg_info) >= 1);
+
+  assert (!DR_CONTROL_ENABLED (dreg_state.dbg_regs[0].ctrl));
+  dreg_state.dbg_regs[0].ctrl |= 1;
+  assert ( DR_CONTROL_ENABLED (dreg_state.dbg_regs[0].ctrl));
+
+  assert (DR_CONTROL_LENGTH (dreg_state.dbg_regs[0].ctrl) == 0);
+  dreg_state.dbg_regs[0].ctrl |= len_mask << 5;
+  assert (DR_CONTROL_LENGTH (dreg_state.dbg_regs[0].ctrl) == len_mask);
+
+  dreg_state.dbg_regs[0].ctrl |= 2 << 3; // write
+  dreg_state.dbg_regs[0].ctrl |= 2 << 1; // GDB: ???: enabled at el0
+  //printf("ctrl=0x%x\n",dreg_state.dbg_regs[0].ctrl);
+  dreg_state.dbg_regs[0].addr = (uintptr_t) addr;
+
+  iov.iov_base = &dreg_state;
+  iov.iov_len = (offsetof (struct user_hwdebug_state, dbg_regs)
+                 + sizeof (dreg_state.dbg_regs[0]));
+  errno = 0;
+  l = ptrace (PTRACE_SETREGSET, pid, NT_ARM_HW_WATCH, &iov);
+  if (errno != 0)
+    error (1, errno, "PTRACE_SETREGSET: NT_ARM_HW_WATCH");
+  assert (l == 0);
+}
+
+#endif
+
+#ifndef SET_WATCHPOINT
+
+int
+main (void)
+{
+  return 77;
+}
+#else
+
+static volatile long long check;
+
+int
+main (void)
+{
+  pid_t got_pid;
+  int i, status;
+  long l;
+
+  atexit (cleanup);
+  signal (SIGABRT, handler_fail);
+  signal (SIGINT, handler_fail);
+
+  child = fork ();
+  assert (child >= 0);
+  if (child == 0)
+    {
+      l = ptrace (PTRACE_TRACEME, 0, NULL, NULL);
+      assert (l == 0);
+      i = raise (SIGUSR1);
+      assert (i == 0);
+      check = -1;
+      i = raise (SIGUSR2);
+      /* NOTREACHED */
+      assert (0);
+    }
+
+  got_pid = waitpid (child, &status, 0);
+  assert (got_pid == child);
+  assert (WIFSTOPPED (status));
+  assert (WSTOPSIG (status) == SIGUSR1);
+
+  // PASS:
+  //SET_WATCHPOINT (child, &check, 0xff);
+  // FAIL:
+  SET_WATCHPOINT (child, &check, 0x02);
+
+  errno = 0;
+  l = ptrace (PTRACE_CONT, child, 0l, 0l);
+  assert_perror (errno);
+  assert (l == 0);
+
+  got_pid = waitpid (child, &status, 0);
+  assert (got_pid == child);
+  assert (WIFSTOPPED (status));
+  if (WSTOPSIG (status) == SIGUSR2)
+    {
+      /* We missed the watchpoint - unsupported by hardware?  */
+      cleanup ();
+      return 2;
+    }
+  assert (WSTOPSIG (status) == SIGTRAP);
+
+  cleanup ();
+  return 0;
+}
+
+#endif
+
diff --git a/gdb/testsuite/gdb.arch/aarch64-dbreg-contents.exp b/gdb/testsuite/gdb.arch/aarch64-dbreg-contents.exp
new file mode 100644
index 0000000..6aa23b0
--- /dev/null
+++ b/gdb/testsuite/gdb.arch/aarch64-dbreg-contents.exp
@@ -0,0 +1,40 @@ 
+# Copyright 2018 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+# Make sure that the inferior doesn't assert and exits successfully.
+
+if {![is_aarch64_target]} {
+    verbose "Skipping ${gdb_test_file_name}."
+    return
+}
+
+standard_testfile .c
+
+if { [gdb_compile ${srcdir}/${subdir}/${srcfile} ${binfile} executable {debug}] != "" } {
+     untested "failed to compile"
+     return -1
+}
+
+clean_restart $testfile
+
+set test "run to exit"
+gdb_test_multiple "run" "$test" {
+    -re "exited with code 01.*$gdb_prompt $" {
+        pass "$test"
+    }
+    -re "exited normally.*$gdb_prompt $" {
+        pass "$test"
+    }
+}