syscalls/ptrace10: Add new regression test

New regression test for a kernel commit:

commit bd14406b78e6daa1ea3c1673bda1ffc9efdeead0
Author: Jiri Olsa <[email protected]>
Date:   Mon Aug 27 11:12:25 2018 +0200

    perf/hw_breakpoint: Modify breakpoint even if the new attr has disabled set

Signed-off-by: Cyril Hrubis <[email protected]>
Reviewed-by: Martin Doucha <[email protected]>
CC: Andy Lutomirski <[email protected]>
CC: Peter Zijlstra <[email protected]>
CC: Thomas Gleixner <[email protected]>
CC: Alexandre Chartre <[email protected]>

runtest/syscalls

@@ -998,6 +998,7 @@ ptrace05 ptrace05
 ptrace07 ptrace07
 ptrace08 ptrace08
 ptrace09 ptrace09
+ptrace10 ptrace10
 
 pwrite01 pwrite01
 pwrite02 pwrite02

testcases/kernel/syscalls/ptrace/.gitignore

@@ -5,3 +5,4 @@
 /ptrace07
 /ptrace08
 /ptrace09
+/ptrace10

testcases/kernel/syscalls/ptrace/ptrace10.c

@@ -0,0 +1,86 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2020 Cyril Hrubis <[email protected]>
+ *
+ * After fix for CVE-2018-1000199 (see ptrace08.c) subsequent calls to POKEUSER
+ * for x86 debug registers were ignored silently.
+ *
+ * This is a regression test for commit:
+ *
+ * commit bd14406b78e6daa1ea3c1673bda1ffc9efdeead0
+ * Author: Jiri Olsa <[email protected]>
+ * Date:   Mon Aug 27 11:12:25 2018 +0200
+ *
+ *     perf/hw_breakpoint: Modify breakpoint even if the new attr has disabled set
+ */
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <stddef.h>
+#include <sys/ptrace.h>
+#include <sys/user.h>
+#include <signal.h>
+#include "tst_test.h"
+
+#if defined(__i386__) || defined(__x86_64__)
+
+static pid_t child_pid;
+
+static void child_main(void)
+{
+	raise(SIGSTOP);
+	exit(0);
+}
+
+static void run(void)
+{
+	int status;
+	unsigned long addr;
+
+	child_pid = SAFE_FORK();
+
+	if (!child_pid)
+		child_main();
+
+	if (SAFE_WAITPID(child_pid, &status, WUNTRACED) != child_pid)
+		tst_brk(TBROK, "Received event from unexpected PID");
+
+	SAFE_PTRACE(PTRACE_ATTACH, child_pid, NULL, NULL);
+	SAFE_PTRACE(PTRACE_POKEUSER, child_pid,
+		(void *)offsetof(struct user, u_debugreg[0]), (void *)1);
+	SAFE_PTRACE(PTRACE_POKEUSER, child_pid,
+		(void *)offsetof(struct user, u_debugreg[0]), (void *)2);
+
+	addr = ptrace(PTRACE_PEEKUSER, child_pid,
+	              (void*)offsetof(struct user, u_debugreg[0]), NULL);
+
+	if (addr == 2)
+		tst_res(TPASS, "The rd0 was set on second PTRACE_POKEUSR");
+	else
+		tst_res(TFAIL, "The rd0 wasn't set on second PTRACE_POKEUSER");
+
+	SAFE_PTRACE(PTRACE_DETACH, child_pid, NULL, NULL);
+	SAFE_KILL(child_pid, SIGCONT);
+	child_pid = 0;
+	tst_reap_children();
+}
+
+static void cleanup(void)
+{
+	/* Main process terminated by tst_brk() with child still paused */
+	if (child_pid)
+		SAFE_KILL(child_pid, SIGKILL);
+}
+
+static struct tst_test test = {
+	.test_all = run,
+	.cleanup = cleanup,
+	.forks_child = 1,
+	.tags = (const struct tst_tag[]) {
+		{"linux-git", "bd14406b78e6"},
+		{}
+	}
+};
+#else
+TST_TEST_TCONF("This test is only supported on x86 systems");
+#endif