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

[Charlie Jenkins <charlie@rivosinc.com>]

On Wed, Jun 19, 2024 at 10:01:47AM +0800, zhouquan@iscas.ac.cn wrote:
> From: Quan Zhou <zhouquan@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.

I don't quite follow what the goal of this test is. With orig_a0 being
added to the previous patch for ptrace, a more constrained test could
ensure that this value is respected.

> 
> 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@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

The gitignore should contain a list of all of the generated binaries
that should be ignored. Can you put ptrace_restart_syscall in here
instead of 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);

How does the value end up being 5?

- Charlie

> +}
> +
> +TEST_HARNESS_MAIN
> -- 
> 2.34.1
>