selftest, ptrace: Add selftest for syscall user dispatch config api

Validate that the following new ptrace requests work as expected

 * PTRACE_GET_SYSCALL_USER_DISPATCH_CONFIG
   returns the contents of task->syscall_dispatch

 * PTRACE_SET_SYSCALL_USER_DISPATCH_CONFIG
   sets the contents of task->syscall_dispatch
Signed-off-by: Gregory Price <gregory.price@memverge.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20230407171834.3558-5-gregory.price@memverge.com

tools/testing/selftests/ptrace/.gitignore

 # SPDX-License-Identifier: GPL-2.0-only
 get_syscall_info
+get_set_sud
 peeksiginfo
 vmaccess

tools/testing/selftests/ptrace/Makefile

 # SPDX-License-Identifier: GPL-2.0-only
 CFLAGS += -std=c99 -pthread -Wall $(KHDR_INCLUDES)
 
-TEST_GEN_PROGS := get_syscall_info peeksiginfo vmaccess
+TEST_GEN_PROGS := get_syscall_info peeksiginfo vmaccess get_set_sud
 
 include ../lib.mk

tools/testing/selftests/ptrace/get_set_sud.c

+// SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
+#include "../kselftest_harness.h"
+#include <stdio.h>
+#include <string.h>
+#include <errno.h>
+#include <sys/wait.h>
+#include <sys/syscall.h>
+#include <sys/prctl.h>
+
+#include "linux/ptrace.h"
+
+static int sys_ptrace(int request, pid_t pid, void *addr, void *data)
+{
+	return syscall(SYS_ptrace, request, pid, addr, data);
+}
+
+TEST(get_set_sud)
+{
+	struct ptrace_sud_config config;
+	pid_t child;
+	int ret = 0;
+	int status;
+
+	child = fork();
+	ASSERT_GE(child, 0);
+	if (child == 0) {
+		ASSERT_EQ(0, sys_ptrace(PTRACE_TRACEME, 0, 0, 0)) {
+			TH_LOG("PTRACE_TRACEME: %m");
+		}
+		kill(getpid(), SIGSTOP);
+		_exit(1);
+	}
+
+	waitpid(child, &status, 0);
+
+	memset(&config, 0xff, sizeof(config));
+	config.mode = PR_SYS_DISPATCH_ON;
+
+	ret = sys_ptrace(PTRACE_GET_SYSCALL_USER_DISPATCH_CONFIG, child,
+			 (void *)sizeof(config), &config);
+
+	ASSERT_EQ(ret, 0);
+	ASSERT_EQ(config.mode, PR_SYS_DISPATCH_OFF);
+	ASSERT_EQ(config.selector, 0);
+	ASSERT_EQ(config.offset, 0);
+	ASSERT_EQ(config.len, 0);
+
+	config.mode = PR_SYS_DISPATCH_ON;
+	config.selector = 0;
+	config.offset = 0x400000;
+	config.len = 0x1000;
+
+	ret = sys_ptrace(PTRACE_SET_SYSCALL_USER_DISPATCH_CONFIG, child,
+			 (void *)sizeof(config), &config);
+
+	ASSERT_EQ(ret, 0);
+
+	memset(&config, 1, sizeof(config));
+	ret = sys_ptrace(PTRACE_GET_SYSCALL_USER_DISPATCH_CONFIG, child,
+			 (void *)sizeof(config), &config);
+
+	ASSERT_EQ(ret, 0);
+	ASSERT_EQ(config.mode, PR_SYS_DISPATCH_ON);
+	ASSERT_EQ(config.selector, 0);
+	ASSERT_EQ(config.offset, 0x400000);
+	ASSERT_EQ(config.len, 0x1000);
+
+	kill(child, SIGKILL);
+}
+
+TEST_HARNESS_MAIN