Re: [PATCH v1 2/2] riscv: selftests: Add a ptrace test to verify syscall parameter modification

[Charlie Jenkins <charlie@rivosinc.com>]

On Thu, Jun 27, 2024 at 11:02:54AM +0800, zhouquan@iscas.ac.cn wrote:
> From: Quan Zhou <zhouquan@iscas.ac.cn>
> 
> This test checks that orig_a0 allows a syscall argument to be modified,
> and that changing a0 does not change the syscall argument.
> 
> Suggested-by: Charlie Jenkins <charlie@rivosinc.com>
> 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 ++
>  tools/testing/selftests/riscv/abi/ptrace.c   | 124 +++++++++++++++++++
>  4 files changed, 138 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.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 $(ARCH),riscv))
> -RISCV_SUBTARGETS ?= hwprobe vector mm sigreturn
> +RISCV_SUBTARGETS ?= hwprobe vector mm sigreturn abi
>  else
>  RISCV_SUBTARGETS :=
>  endif
> diff --git a/tools/testing/selftests/riscv/abi/.gitignore b/tools/testing/selftests/riscv/abi/.gitignore
> new file mode 100644
> index 000000000000..d61c51358965
> --- /dev/null
> +++ b/tools/testing/selftests/riscv/abi/.gitignore
> @@ -0,0 +1 @@
> +ptrace
> diff --git a/tools/testing/selftests/riscv/abi/Makefile b/tools/testing/selftests/riscv/abi/Makefile
> new file mode 100644
> index 000000000000..808d48a91ad7
> --- /dev/null
> +++ b/tools/testing/selftests/riscv/abi/Makefile
> @@ -0,0 +1,12 @@
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (C) 2021 ARM Limited
> +# Originally tools/testing/arm64/abi/Makefile
> +
> +CFLAGS += -I$(top_srcdir)/tools/include
> +
> +TEST_GEN_PROGS := ptrace
> +
> +include ../../lib.mk
> +
> +$(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 000000000000..f85f927cd685
> --- /dev/null
> +++ b/tools/testing/selftests/riscv/abi/ptrace.c
> @@ -0,0 +1,124 @@
> +// 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_MODIFY      0x01
> +#define A0_MODIFY           0x02
> +#define A0_OLD              0x03
> +#define A0_NEW              0x04
> +
> +#define perr_and_exit(fmt, ...)					\
> +	({								\
> +	 	char buf[256];						\

Apologies, I missed this in the last review. In the above line there is
a space in the middle of the tabs before `char buf[256];`.

> +		snprintf(buf, sizeof(buf), "%s:%d: " fmt ": %m\n",	\
> +			__func__, __LINE__, ##__VA_ARGS__);		\
> +		perror(buf);						\
> +		exit(-1);						\
> +	})
> +
> +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, int *result)
> +{
> +	int status;
> +	pid_t pid;
> +	struct user_regs_struct regs;
> +	struct iovec iov = {
> +		.iov_base = &regs,
> +		.iov_len = sizeof(regs),
> +	};
> +
> +	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)
> +		exit(1);
> +
> +	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 orig_a0 before the syscall */
> +	if (ptrace(PTRACE_GETREGSET, pid, NT_PRSTATUS, &iov))
> +		perr_and_exit("failed to get tracee registers\n");
> +	if (regs.orig_a0 != A0_OLD)
> +		perr_and_exit("unexpected orig_a0: 0x%lx\n", regs.orig_a0);
> +
> +	/* Modify a0/orig_a0 for the syscall */
> +	switch (opt) {
> +	case A0_MODIFY:
> +		regs.a0 = A0_NEW;
> +		break;
> +	case ORIG_A0_MODIFY:
> +		regs.orig_a0 = A0_NEW;
> +		break;
> +	}
> +
> +	if (ptrace(PTRACE_SETREGSET, pid, NT_PRSTATUS, &iov))
> +		perr_and_exit("failed to set tracee registers\n");
> +
> +	/* 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");
> +
> +	*result = WEXITSTATUS(status);
> +}
> +
> +TEST(ptrace_modify_a0)
> +{
> +	int result;
> +
> +	ptrace_test(A0_MODIFY, &result);
> +
> +	/* The modification of a0 cannot affect the first argument of the syscall */
> +	EXPECT_EQ(A0_OLD, result);
> +}
> +
> +TEST(ptrace_modify_orig_a0)
> +{
> +	int result;
> +
> +	ptrace_test(ORIG_A0_MODIFY, &result);
> +
> +	/* Only modify orig_a0 to change the first argument of the syscall */
> +	EXPECT_EQ(A0_NEW, result);
> +}
> +
> +TEST_HARNESS_MAIN
> -- 
> 2.34.1
> 

Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>