[RFC PATCH 2/2] riscv: selftests: Add a ptrace test to check a0 of restarted syscall

[zhouquan at iscas.ac.cn]

From: Quan Zhou <zhouquan at iscas.ac.cn>

This test creates two processes: a tracer and a tracee. The tracer actively
sends a SIGUSR1 signal in user mode to interrupt the read syscall being
executed by the tracee. We will reset a0/orig_a0 and then observe the value
of a0 held by the restarted read syscall.

Compared to the test program, a more common scenario is the use of the
exece syscall, which sends a signal in the kernel path to restart
the syscall.

Signed-off-by: Quan Zhou <zhouquan at iscas.ac.cn>
---
 tools/testing/selftests/riscv/Makefile        |   2 +-
 tools/testing/selftests/riscv/abi/.gitignore  |   1 +
 tools/testing/selftests/riscv/abi/Makefile    |  12 ++
 .../riscv/abi/ptrace_restart_syscall.c        | 148 ++++++++++++++++++
 4 files changed, 162 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/riscv/abi/.gitignore
 create mode 100644 tools/testing/selftests/riscv/abi/Makefile
 create mode 100644 tools/testing/selftests/riscv/abi/ptrace_restart_syscall.c

diff --git a/tools/testing/selftests/riscv/Makefile b/tools/testing/selftests/riscv/Makefile
index 7ce03d832b64..98541dc2f164 100644
--- a/tools/testing/selftests/riscv/Makefile
+++ b/tools/testing/selftests/riscv/Makefile
@@ -5,7 +5,7 @@
 ARCH ?= $(shell uname -m 2>/dev/null || echo not)
 
 ifneq (,$(filter $(ARCH),riscv))
-RISCV_SUBTARGETS ?= hwprobe vector mm sigreturn
+RISCV_SUBTARGETS ?= hwprobe vector mm sigreturn abi
 else
 RISCV_SUBTARGETS :=
 endif
diff --git a/tools/testing/selftests/riscv/abi/.gitignore b/tools/testing/selftests/riscv/abi/.gitignore
new file mode 100644
index 000000000000..e1e00ffb9db9
--- /dev/null
+++ b/tools/testing/selftests/riscv/abi/.gitignore
@@ -0,0 +1 @@
+abi
diff --git a/tools/testing/selftests/riscv/abi/Makefile b/tools/testing/selftests/riscv/abi/Makefile
new file mode 100644
index 000000000000..634fa7de74e6
--- /dev/null
+++ b/tools/testing/selftests/riscv/abi/Makefile
@@ -0,0 +1,12 @@
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (C) 2021 ARM Limited
+# Originally tools/testing/arm64/abi/Makefile
+
+CFLAGS += -I$(top_srcdir)/tools/include
+
+TEST_GEN_PROGS := ptrace_restart_syscall
+
+include ../../lib.mk
+
+$(OUTPUT)/ptrace_restart_syscall: ptrace_restart_syscall.c
+	$(CC) -static -o$@ $(CFLAGS) $(LDFLAGS) $^
diff --git a/tools/testing/selftests/riscv/abi/ptrace_restart_syscall.c b/tools/testing/selftests/riscv/abi/ptrace_restart_syscall.c
new file mode 100644
index 000000000000..3e25548cb95e
--- /dev/null
+++ b/tools/testing/selftests/riscv/abi/ptrace_restart_syscall.c
@@ -0,0 +1,148 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <signal.h>
+#include <errno.h>
+#include <sys/types.h>
+#include <sys/ptrace.h>
+#include <sys/stat.h>
+#include <sys/user.h>
+#include <sys/wait.h>
+#include <sys/uio.h>
+#include <linux/elf.h>
+#include <linux/unistd.h>
+#include <asm/ptrace.h>
+
+#include "../../kselftest_harness.h"
+
+#define ORIG_A0_AFTER_MODIFIED  0x5
+#define MODIFY_A0               0x01
+#define MODIFY_ORIG_A0          0x02
+
+#define perr_and_exit(fmt, ...) do {			\
+	char buf[256];					\
+	snprintf(buf, sizeof(buf), "%s:%d: " fmt ": %m\n",	\
+			__func__, __LINE__, ##__VA_ARGS__);	\
+	perror(buf);						\
+	exit(-1);						\
+} while (0)
+
+static inline void resume_and_wait_tracee(pid_t pid, int flag)
+{
+	int status;
+
+	if (ptrace(flag, pid, 0, 0))
+		perr_and_exit("failed to resume the tracee %d", pid);
+
+	if (waitpid(pid, &status, 0) != pid)
+		perr_and_exit("failed to wait for the tracee %d", pid);
+}
+
+static void ptrace_restart_syscall(int opt, int *result)
+{
+	int status;
+	int p[2], fd_zero;
+	pid_t pid;
+
+	struct user_regs_struct regs;
+	struct iovec iov = {
+		.iov_base = &regs,
+		.iov_len = sizeof(regs),
+	};
+
+	if (pipe(p))
+		perr_and_exit("failed to create a pipe");
+
+	fd_zero = open("/dev/zero", O_RDONLY);
+	if (fd_zero < 0)
+		perr_and_exit("failed to open /dev/zero");
+
+	pid = fork();
+	if (pid == 0) {
+		char c;
+
+		/* Mark oneself being traced */
+		if (ptrace(PTRACE_TRACEME, 0, 0, 0))
+			perr_and_exit("failed to request for tracer to trace me");
+
+		kill(getpid(), SIGSTOP);
+
+		if (read(p[0], &c, 1) != 1)
+			exit(1);
+
+		exit(0);
+	} else if (pid < 0)
+		exit(1);
+
+	if (waitpid(pid, &status, 0) != pid)
+		perr_and_exit("failed to wait for the tracee %d\n", pid);
+
+	/* Resume the tracee until the next syscall */
+	resume_and_wait_tracee(pid, PTRACE_SYSCALL);
+
+	/* Deliver a signal to interrupt the syscall */
+	kill(pid, SIGUSR1);
+
+	/* The tracee stops at syscall exit */
+	resume_and_wait_tracee(pid, PTRACE_SYSCALL);
+
+	/* Check tracee orig_a0 before syscall restart */
+	if (ptrace(PTRACE_GETREGSET, pid, NT_PRSTATUS, &iov))
+		perr_and_exit("failed to get tracee registers");
+	if (regs.orig_a0 != p[0])
+		perr_and_exit("unexpected a0");
+
+	/* Modify a0/orig_a0 for the restarted syscall */
+	switch (opt) {
+	case MODIFY_A0:
+		regs.a0 = fd_zero;
+		break;
+	case MODIFY_ORIG_A0:
+		regs.orig_a0 = fd_zero;
+		break;
+	}
+
+	if (ptrace(PTRACE_SETREGSET, pid, NT_PRSTATUS, &iov))
+		perr_and_exit("failed to set tracee registers");
+
+	/* Ignore SIGUSR1 signal */
+	resume_and_wait_tracee(pid, PTRACE_SYSCALL);
+
+	/* Stop at the entry point of the restarted syscall */
+	resume_and_wait_tracee(pid, PTRACE_SYSCALL);
+
+	/* Now, check regs.a0 of the restarted syscall */
+	if (ptrace(PTRACE_GETREGSET, pid, NT_PRSTATUS, &iov))
+		perr_and_exit("failed to get tracee registers");
+	*result = regs.a0;
+
+	/* Resume the tracee */
+	ptrace(PTRACE_CONT, pid, 0, 0);
+	if (waitpid(pid, &status, 0) != pid)
+		perr_and_exit("failed to wait for the tracee");
+}
+
+TEST(ptrace_modify_a0)
+{
+	int result;
+
+	ptrace_restart_syscall(MODIFY_A0, &result);
+
+	/* The tracer's modification of a0 cannot affect the restarted tracee */
+	EXPECT_NE(ORIG_A0_AFTER_MODIFIED, result);
+}
+
+TEST(ptrace_modify_orig_a0)
+{
+	int result;
+
+	ptrace_restart_syscall(MODIFY_ORIG_A0, &result);
+
+	/* The tracer must modify orig_a0 to actually change the tracee's a0 */
+	EXPECT_EQ(ORIG_A0_AFTER_MODIFIED, result);
+}
+
+TEST_HARNESS_MAIN
-- 
2.34.1