svn commit: r325028 - in head: sys/kern sys/sys tests/sys/kern
John Baldwin
jhb at FreeBSD.org
Fri Oct 27 03:16:20 UTC 2017
Author: jhb
Date: Fri Oct 27 03:16:19 2017
New Revision: 325028
URL: https://svnweb.freebsd.org/changeset/base/325028
Log:
Discard the correct thread event reported for a ptrace stop.
When multiple threads wish to report a tracing event to a debugger,
both threads call ptracestop() and one thread will win the race to be
the reporting thread (p->p_xthread). The debugger uses PT_LWPINFO
with the process ID to determine which thread / LWP is reporting an
event and the details of that event. This event is cleared as a side
effect of the subsequent ptrace event that resumed the process
(PT_CONTINUE, PT_STEP, etc.). However, ptrace() was clearing the
event identified by the LWP ID passed to the resume request even if
that wasn't the 'p_xthread'. This could result in clearing an event
that had not yet been observed by the debugger and leaving the
existing event for 'p_thread' pending so that it was reported a second
time.
Specifically, if the debugger stopped due to a software breakpoint in
one thread, but then switched to another thread that was used to
resume (e.g. if the user switched to a different thread and issued a
step), the resume request (PT_STEP) cleared a pending event (if any)
for the thread being stepped. However, the process immediately
stopped and the first thread reported it's breakpoint event a second
time. The debugger decremented the PC for "both" breakpoint events
which resulted in the PC now pointing into the middle of an
instruction (on x86) and a SIGILL fault when the process was resumed a
second time.
To fix, always clear the pending event for 'p_xthread' when resuming a
process. ptrace() still honors the requested LWP ID when enabling
single-stepping (PT_STEP) or setting a different PC (PT_CONTINUE).
Reported by: GDB testsuite (gdb.threads/continue-pending-status.exp)
Reviewed by: kib
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D12794
Modified:
head/sys/kern/sys_process.c
head/sys/sys/param.h
head/tests/sys/kern/ptrace_test.c
Modified: head/sys/kern/sys_process.c
==============================================================================
--- head/sys/kern/sys_process.c Thu Oct 26 22:53:55 2017 (r325027)
+++ head/sys/kern/sys_process.c Fri Oct 27 03:16:19 2017 (r325028)
@@ -1129,6 +1129,13 @@ kern_ptrace(struct thread *td, int req, pid_t pid, voi
}
sendsig:
+ /*
+ * Clear the pending event for the thread that just
+ * reported its event (p_xthread). This may not be
+ * the thread passed to PT_CONTINUE, PT_STEP, etc. if
+ * the debugger is resuming a different thread.
+ */
+ td2 = p->p_xthread;
if (proctree_locked) {
sx_xunlock(&proctree_lock);
proctree_locked = 0;
Modified: head/sys/sys/param.h
==============================================================================
--- head/sys/sys/param.h Thu Oct 26 22:53:55 2017 (r325027)
+++ head/sys/sys/param.h Fri Oct 27 03:16:19 2017 (r325028)
@@ -58,7 +58,7 @@
* in the range 5 to 9.
*/
#undef __FreeBSD_version
-#define __FreeBSD_version 1200051 /* Master, propagated to newvers */
+#define __FreeBSD_version 1200052 /* Master, propagated to newvers */
/*
* __FreeBSD_kernel__ indicates that this system uses the kernel of FreeBSD,
Modified: head/tests/sys/kern/ptrace_test.c
==============================================================================
--- head/tests/sys/kern/ptrace_test.c Thu Oct 26 22:53:55 2017 (r325027)
+++ head/tests/sys/kern/ptrace_test.c Fri Oct 27 03:16:19 2017 (r325028)
@@ -3463,6 +3463,174 @@ ATF_TC_BODY(ptrace__PT_STEP_with_signal, tc)
ATF_REQUIRE(errno == ECHILD);
}
+#if defined(__amd64__) || defined(__i386__)
+/*
+ * Only x86 both define breakpoint() and have a PC after breakpoint so
+ * that restarting doesn't retrigger the breakpoint.
+ */
+static void *
+continue_thread(void *arg)
+{
+ breakpoint();
+ return (NULL);
+}
+
+static __dead2 void
+continue_thread_main(void)
+{
+ pthread_t threads[2];
+
+ CHILD_REQUIRE(pthread_create(&threads[0], NULL, continue_thread,
+ NULL) == 0);
+ CHILD_REQUIRE(pthread_create(&threads[1], NULL, continue_thread,
+ NULL) == 0);
+ CHILD_REQUIRE(pthread_join(threads[0], NULL) == 0);
+ CHILD_REQUIRE(pthread_join(threads[1], NULL) == 0);
+ exit(1);
+}
+
+/*
+ * Ensure that PT_CONTINUE clears the status of the thread that
+ * triggered the stop even if a different thread's LWP was passed to
+ * PT_CONTINUE.
+ */
+ATF_TC_WITHOUT_HEAD(ptrace__PT_CONTINUE_different_thread);
+ATF_TC_BODY(ptrace__PT_CONTINUE_different_thread, tc)
+{
+ struct ptrace_lwpinfo pl;
+ pid_t fpid, wpid;
+ lwpid_t lwps[2];
+ bool hit_break[2];
+ int i, j, status;
+
+ ATF_REQUIRE((fpid = fork()) != -1);
+ if (fpid == 0) {
+ trace_me();
+ continue_thread_main();
+ }
+
+ /* The first wait() should report the stop from SIGSTOP. */
+ wpid = waitpid(fpid, &status, 0);
+ ATF_REQUIRE(wpid == fpid);
+ ATF_REQUIRE(WIFSTOPPED(status));
+ ATF_REQUIRE(WSTOPSIG(status) == SIGSTOP);
+
+ ATF_REQUIRE(ptrace(PT_LWPINFO, wpid, (caddr_t)&pl,
+ sizeof(pl)) != -1);
+
+ ATF_REQUIRE(ptrace(PT_LWP_EVENTS, wpid, NULL, 1) == 0);
+
+ /* Continue the child ignoring the SIGSTOP. */
+ ATF_REQUIRE(ptrace(PT_CONTINUE, fpid, (caddr_t)1, 0) == 0);
+
+ /* One of the new threads should report it's birth. */
+ wpid = waitpid(fpid, &status, 0);
+ ATF_REQUIRE(wpid == fpid);
+ ATF_REQUIRE(WIFSTOPPED(status));
+ ATF_REQUIRE(WSTOPSIG(status) == SIGTRAP);
+
+ ATF_REQUIRE(ptrace(PT_LWPINFO, wpid, (caddr_t)&pl, sizeof(pl)) != -1);
+ ATF_REQUIRE((pl.pl_flags & (PL_FLAG_BORN | PL_FLAG_SCX)) ==
+ (PL_FLAG_BORN | PL_FLAG_SCX));
+ lwps[0] = pl.pl_lwpid;
+
+ /*
+ * Suspend this thread to ensure both threads are alive before
+ * hitting the breakpoint.
+ */
+ ATF_REQUIRE(ptrace(PT_SUSPEND, lwps[0], NULL, 0) != -1);
+
+ ATF_REQUIRE(ptrace(PT_CONTINUE, fpid, (caddr_t)1, 0) == 0);
+
+ /* Second thread should report it's birth. */
+ wpid = waitpid(fpid, &status, 0);
+ ATF_REQUIRE(wpid == fpid);
+ ATF_REQUIRE(WIFSTOPPED(status));
+ ATF_REQUIRE(WSTOPSIG(status) == SIGTRAP);
+
+ ATF_REQUIRE(ptrace(PT_LWPINFO, wpid, (caddr_t)&pl, sizeof(pl)) != -1);
+ ATF_REQUIRE((pl.pl_flags & (PL_FLAG_BORN | PL_FLAG_SCX)) ==
+ (PL_FLAG_BORN | PL_FLAG_SCX));
+ ATF_REQUIRE(pl.pl_lwpid != lwps[0]);
+ lwps[1] = pl.pl_lwpid;
+
+ /* Resume both threads waiting for breakpoint events. */
+ hit_break[0] = hit_break[1] = false;
+ ATF_REQUIRE(ptrace(PT_RESUME, lwps[0], NULL, 0) != -1);
+ ATF_REQUIRE(ptrace(PT_CONTINUE, fpid, (caddr_t)1, 0) == 0);
+
+ /* One thread should report a breakpoint. */
+ wpid = waitpid(fpid, &status, 0);
+ ATF_REQUIRE(wpid == fpid);
+ ATF_REQUIRE(WIFSTOPPED(status));
+ ATF_REQUIRE(WSTOPSIG(status) == SIGTRAP);
+
+ ATF_REQUIRE(ptrace(PT_LWPINFO, wpid, (caddr_t)&pl, sizeof(pl)) != -1);
+ ATF_REQUIRE((pl.pl_flags & PL_FLAG_SI) != 0);
+ ATF_REQUIRE(pl.pl_siginfo.si_signo == SIGTRAP &&
+ pl.pl_siginfo.si_code == TRAP_BRKPT);
+ if (pl.pl_lwpid == lwps[0])
+ i = 0;
+ else
+ i = 1;
+ hit_break[i] = true;
+
+ /*
+ * Resume both threads but pass the other thread's LWPID to
+ * PT_CONTINUE.
+ */
+ ATF_REQUIRE(ptrace(PT_CONTINUE, lwps[i ^ 1], (caddr_t)1, 0) == 0);
+
+ /*
+ * Will now get two thread exit events and one more breakpoint
+ * event.
+ */
+ for (j = 0; j < 3; j++) {
+ wpid = waitpid(fpid, &status, 0);
+ ATF_REQUIRE(wpid == fpid);
+ ATF_REQUIRE(WIFSTOPPED(status));
+ ATF_REQUIRE(WSTOPSIG(status) == SIGTRAP);
+
+ ATF_REQUIRE(ptrace(PT_LWPINFO, wpid, (caddr_t)&pl,
+ sizeof(pl)) != -1);
+
+ if (pl.pl_lwpid == lwps[0])
+ i = 0;
+ else
+ i = 1;
+
+ ATF_REQUIRE_MSG(lwps[i] != 0, "event for exited thread");
+ if (pl.pl_flags & PL_FLAG_EXITED) {
+ ATF_REQUIRE_MSG(hit_break[i],
+ "exited thread did not report breakpoint");
+ lwps[i] = 0;
+ } else {
+ ATF_REQUIRE((pl.pl_flags & PL_FLAG_SI) != 0);
+ ATF_REQUIRE(pl.pl_siginfo.si_signo == SIGTRAP &&
+ pl.pl_siginfo.si_code == TRAP_BRKPT);
+ ATF_REQUIRE_MSG(!hit_break[i],
+ "double breakpoint event");
+ hit_break[i] = true;
+ }
+
+ ATF_REQUIRE(ptrace(PT_CONTINUE, fpid, (caddr_t)1, 0) == 0);
+ }
+
+ /* Both threads should have exited. */
+ ATF_REQUIRE(lwps[0] == 0);
+ ATF_REQUIRE(lwps[1] == 0);
+
+ /* The last event should be for the child process's exit. */
+ wpid = waitpid(fpid, &status, 0);
+ ATF_REQUIRE(WIFEXITED(status));
+ ATF_REQUIRE(WEXITSTATUS(status) == 1);
+
+ wpid = wait(&status);
+ ATF_REQUIRE(wpid == -1);
+ ATF_REQUIRE(errno == ECHILD);
+}
+#endif
+
ATF_TP_ADD_TCS(tp)
{
@@ -3515,6 +3683,9 @@ ATF_TP_ADD_TCS(tp)
ATF_TP_ADD_TC(tp, ptrace__event_mask_sigkill_discard);
ATF_TP_ADD_TC(tp, ptrace__PT_ATTACH_with_SBDRY_thread);
ATF_TP_ADD_TC(tp, ptrace__PT_STEP_with_signal);
+#if defined(__amd64__) || defined(__i386__)
+ ATF_TP_ADD_TC(tp, ptrace__PT_CONTINUE_different_thread);
+#endif
return (atf_no_error());
}
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