[PATCH v4 2/2] riscv: selftests: Add a ptrace test to verify syscall parameter modification

[Celeste Liu <uwu@coelacanthus.name>]

This test checks that orig_a0 allows a syscall argument to be modified,
and that changing a0 does not change the syscall argument.

Co-developed-by: Quan Zhou <zhouquan@iscas.ac.cn>
Signed-off-by: Quan Zhou <zhouquan@iscas.ac.cn>
Co-developed-by: Charlie Jenkins <charlie@rivosinc.com>
Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
Reviewed-by: Björn Töpel <bjorn@rivosinc.com>
Signed-off-by: Celeste Liu <uwu@coelacanthus.name>
---
 tools/testing/selftests/riscv/abi/.gitignore |   1 +
 tools/testing/selftests/riscv/abi/Makefile   |   5 +-
 tools/testing/selftests/riscv/abi/ptrace.c   | 151 +++++++++++++++++++++++++++
 3 files changed, 156 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/riscv/abi/.gitignore b/tools/testing/selftests/riscv/abi/.gitignore
index b38358f91c4d2240ae64892871d9ca98bda1ae58..378c605919a3b3d58eec2701eb7af430cfe315d6 100644
--- a/tools/testing/selftests/riscv/abi/.gitignore
+++ b/tools/testing/selftests/riscv/abi/.gitignore
@@ -1 +1,2 @@
 pointer_masking
+ptrace
diff --git a/tools/testing/selftests/riscv/abi/Makefile b/tools/testing/selftests/riscv/abi/Makefile
index ed82ff9c664e7eb3f760cbab81fb957ff72579c5..3f74d059dfdcbce4d45d8ff618781ccea1419061 100644
--- a/tools/testing/selftests/riscv/abi/Makefile
+++ b/tools/testing/selftests/riscv/abi/Makefile
@@ -2,9 +2,12 @@
 
 CFLAGS += -I$(top_srcdir)/tools/include
 
-TEST_GEN_PROGS := pointer_masking
+TEST_GEN_PROGS := pointer_masking ptrace
 
 include ../../lib.mk
 
 $(OUTPUT)/pointer_masking: pointer_masking.c
 	$(CC) -static -o$@ $(CFLAGS) $(LDFLAGS) $^
+
+$(OUTPUT)/ptrace: ptrace.c
+	$(CC) -static -o$@ $(CFLAGS) $(LDFLAGS) $^
diff --git a/tools/testing/selftests/riscv/abi/ptrace.c b/tools/testing/selftests/riscv/abi/ptrace.c
new file mode 100644
index 0000000000000000000000000000000000000000..023695352215bb5de3f91c1a6f5ea3b4f9373ff9
--- /dev/null
+++ b/tools/testing/selftests/riscv/abi/ptrace.c
@@ -0,0 +1,151 @@
+// 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 <linux/ptrace.h>
+#include <asm/ptrace.h>
+
+#include "../../kselftest_harness.h"
+
+#define ORIG_A0_MODIFY      0x01
+#define A0_MODIFY           0x02
+#define A0_OLD              0x03
+#define A0_NEW              0x04
+
+struct a0_regs {
+	__s64 orig_a0;
+	__u64 a0;
+};
+
+#define perr_and_exit(fmt, ...)						\
+	({								\
+		char buf[256];						\
+		snprintf(buf, sizeof(buf), "%s:%d:" fmt ": %m\n",	\
+			__func__, __LINE__, ##__VA_ARGS__);		\
+		ksft_exit_fail_perror(buf);				\
+	})
+
+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\n", pid);
+
+	if (waitpid(pid, &status, 0) != pid)
+		perr_and_exit("failed to wait for the tracee %d\n", pid);
+}
+
+static void ptrace_test(int opt, struct a0_regs *result)
+{
+	int status;
+	pid_t pid;
+	struct user_regs_struct regs;
+	struct iovec iov = {
+		.iov_base = &regs,
+		.iov_len = sizeof(regs),
+	};
+
+	unsigned long orig_a0;
+	struct iovec a0_iov = {
+		.iov_base = &orig_a0,
+		.iov_len = sizeof(orig_a0),
+	};
+	struct ptrace_syscall_info syscall_info_entry, syscall_info_exit;
+
+	pid = fork();
+	if (pid == 0) {
+		/* Mark oneself being traced */
+		long val = ptrace(PTRACE_TRACEME, 0, 0, 0);
+
+		if (val)
+			perr_and_exit("failed to request for tracer to trace me: %ld\n", val);
+
+		kill(getpid(), SIGSTOP);
+
+		/* Perform exit syscall that will be intercepted */
+		exit(A0_OLD);
+	}
+
+	if (pid < 0)
+		ksft_exit_fail_perror("failed to fork");
+
+	if (waitpid(pid, &status, 0) != pid)
+		perr_and_exit("failed to wait for the tracee %d\n", pid);
+
+	/* Stop at the entry point of the syscall */
+	resume_and_wait_tracee(pid, PTRACE_SYSCALL);
+
+	/* Check tracee regs before the syscall */
+	if (ptrace(PTRACE_GETREGSET, pid, NT_PRSTATUS, &iov))
+		perr_and_exit("failed to get tracee registers\n");
+	if (ptrace(PTRACE_GETREGSET, pid, NT_RISCV_ORIG_A0, &a0_iov))
+		perr_and_exit("failed to get tracee registers\n");
+	if (orig_a0 != A0_OLD)
+		perr_and_exit("unexpected orig_a0: 0x%lx\n", orig_a0);
+
+	/* Modify a0/orig_a0 for the syscall */
+	switch (opt) {
+	case A0_MODIFY:
+		regs.a0 = A0_NEW;
+		break;
+	case ORIG_A0_MODIFY:
+		orig_a0 = A0_NEW;
+		break;
+	}
+
+	if (ptrace(PTRACE_SETREGSET, pid, NT_PRSTATUS, &iov))
+		perr_and_exit("failed to set tracee registers\n");
+	if (ptrace(PTRACE_SETREGSET, pid, NT_RISCV_ORIG_A0, &a0_iov))
+		perr_and_exit("failed to set tracee registers\n");
+
+	if (ptrace(PTRACE_GET_SYSCALL_INFO, pid, PTRACE_SYSCALL_INFO_ENTRY, &syscall_info_entry))
+		perr_and_exit("failed to get syscall info of entry\n");
+	result->orig_a0 = syscall_info_entry->entry.args[0];
+	if (ptrace(PTRACE_GET_SYSCALL_INFO, pid, PTRACE_SYSCALL_INFO_EXIT, &syscall_info_exit))
+		perr_and_exit("failed to get syscall info of exit\n");
+	result->a0 = syscall_info_exit->exit.rval;
+
+	/* Resume the tracee */
+	ptrace(PTRACE_CONT, pid, 0, 0);
+	if (waitpid(pid, &status, 0) != pid)
+		perr_and_exit("failed to wait for the tracee\n");
+
+}
+
+TEST(ptrace_modify_a0)
+{
+	struct a0_regs result;
+
+	ptrace_test(A0_MODIFY, &result);
+
+	/* The modification of a0 cannot affect the first argument of the syscall */
+	EXPECT_EQ(A0_OLD, result.orig_a0);
+	EXPECT_EQ(A0_NEW, result.a0);
+}
+
+TEST(ptrace_modify_orig_a0)
+{
+	struct a0_regs result;
+
+	ptrace_test(ORIG_A0_MODIFY, &result);
+
+	/* Only modify orig_a0 to change the first argument of the syscall */
+	EXPECT_EQ(A0_NEW, result.orig_a0);
+	/* a0 will keep default value, orig_a0 or -ENOSYS, depends on internal. */
+	EXPECT_NE(A0_NEW, result.a0);
+}
+
+TEST_HARNESS_MAIN

-- 
2.47.1