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Message-ID: <ZnOaBeNnNpvrE5ss@ghost>
Date: Wed, 19 Jun 2024 19:55:01 -0700
From: Charlie Jenkins <charlie@...osinc.com>
To: zhouquan@...as.ac.cn
Cc: linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
linux-kselftest@...r.kernel.org, oleg@...hat.com,
paul.walmsley@...ive.com, palmer@...belt.com, aou@...s.berkeley.edu,
andy.chiu@...ive.com, shuah@...nel.org
Subject: Re: [RFC PATCH 2/2] riscv: selftests: Add a ptrace test to check a0
of restarted syscall
On Wed, Jun 19, 2024 at 10:01:47AM +0800, zhouquan@...as.ac.cn wrote:
> From: Quan Zhou <zhouquan@...as.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@...as.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 = ®s,
> + .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
>
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