Message-ID: <20250115-28c95808502d43f84b3fe0a6@orel>
Date: Wed, 15 Jan 2025 10:14:02 +0100
From: Andrew Jones <ajones@...tanamicro.com>
To: Celeste Liu <uwu@...lacanthus.name>
Cc: Oleg Nesterov <oleg@...hat.com>, 
	Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>, 
	Eric Biederman <ebiederm@...ssion.com>, Kees Cook <kees@...nel.org>, Shuah Khan <shuah@...nel.org>, 
	Albert Ou <aou@...s.berkeley.edu>, Alexandre Ghiti <alex@...ti.fr>, 
	"Dmitry V. Levin" <ldv@...ace.io>, Andrea Bolognani <abologna@...hat.com>, 
	Björn Töpel <bjorn@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Ron Economos <re@...z.net>, 
	Charlie Jenkins <charlie@...osinc.com>, Quan Zhou <zhouquan@...as.ac.cn>, 
	Felix Yan <felixonmars@...hlinux.org>, Ruizhe Pan <c141028@...il.com>, Guo Ren <guoren@...nel.org>, 
	Yao Zi <ziyao@...root.org>, linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org, linux-kselftest@...r.kernel.org, 
	Björn Töpel <bjorn@...osinc.com>
Subject: Re: [PATCH v5 2/2] riscv: selftests: Add a ptrace test to verify a0
 and orig_a0 access

On Wed, Jan 15, 2025 at 04:24:59AM +0800, Celeste Liu wrote:
> This test checks that orig_a0 and a0 can be modified and accessed
> independently.
> 
> Co-developed-by: Quan Zhou <zhouquan@...as.ac.cn>
> Signed-off-by: Quan Zhou <zhouquan@...as.ac.cn>
> Co-developed-by: Charlie Jenkins <charlie@...osinc.com>
> Signed-off-by: Charlie Jenkins <charlie@...osinc.com>
> Reviewed-by: Björn Töpel <bjorn@...osinc.com>
> Signed-off-by: Celeste Liu <uwu@...lacanthus.name>
> ---
>  tools/testing/selftests/riscv/abi/.gitignore |   1 +
>  tools/testing/selftests/riscv/abi/Makefile   |   6 +-
>  tools/testing/selftests/riscv/abi/ptrace.c   | 201 +++++++++++++++++++++++++++
>  3 files changed, 207 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..359a082c88a401883fb3776b35e4dacf69beaaaa 100644
> --- a/tools/testing/selftests/riscv/abi/Makefile
> +++ b/tools/testing/selftests/riscv/abi/Makefile
> @@ -1,10 +1,14 @@
>  # SPDX-License-Identifier: GPL-2.0
>  
>  CFLAGS += -I$(top_srcdir)/tools/include
> +CFLAGS += $(KHDR_INCLUDES)
>  
> -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..f1a0458adccdd040bfaa350e2e8d98b1ef34c0ad
> --- /dev/null
> +++ b/tools/testing/selftests/riscv/abi/ptrace.c
> @@ -0,0 +1,201 @@
> +// 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"
> +
> +#ifndef sizeof_field
> +#define sizeof_field(TYPE, MEMBER) sizeof((((TYPE *)0)->MEMBER))
> +#endif
> +#ifndef offsetofend
> +#define offsetofend(TYPE, MEMBER) \
> +	(offsetof(TYPE, MEMBER) + sizeof_field(TYPE, MEMBER))
> +#endif

I think this is the sixth test to define these. We should copy
include/linux/stddef.h into tools/include. We already have
tools/include/uapi/linux/stddef.h with __struct_group and
__DECLARE_FLEX_ARRAY, so I think it should just work.

> +
> +
> +#define ORIG_A0_MODIFY      0x01
> +#define A0_MODIFY           0x02
> +#define A0_OLD              0xbadbeefbeeff
> +#define A0_NEW              0xffeebfeebdab
> +
> +
> +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 void ptrace_test(int opt, struct a0_regs result[])
> +{
> +	int status;
> +	long rc;
> +	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 = {
> +		.op = 0xff,
> +	};
> +	const unsigned int expected_sci_entry_size =
> +		offsetofend(struct ptrace_syscall_info, entry.args);
> +	const unsigned int expected_sci_exit_size =
> +		offsetofend(struct ptrace_syscall_info, exit.is_error);
> +
> +	pid = fork();
> +	if (pid == 0) {
> +		/* Mark oneself being traced */
> +		long val = ptrace(PTRACE_TRACEME, 0, 0, 0);
> +
> +		if (val < 0)
> +			perr_and_exit("failed to request for tracer to trace me: %ld", val);
> +
> +		kill(getpid(), SIGSTOP);
> +
> +		/* Perform chdir syscall that will be intercepted */
> +		syscall(__NR_chdir, A0_OLD);
> +
> +		exit(0);
> +	}
> +
> +	if (pid < 0)
> +		ksft_exit_fail_perror("failed to fork");
> +
> +	for (int i = 0; i < 3; i++) {
> +		if (waitpid(pid, &status, 0) != pid)
> +			perr_and_exit("failed to wait for the tracee %d", pid);
> +		if (WIFSTOPPED(status)) {
> +			switch (WSTOPSIG(status)) {
> +			case SIGSTOP:
> +				if (ptrace(PTRACE_SETOPTIONS, pid, 0, PTRACE_O_TRACESYSGOOD) < 0)
> +					perr_and_exit("failed to set PTRACE_O_TRACESYSGOOD");
> +				break;
> +			case SIGTRAP|0x80:
> +				/* Modify twice so GET_SYSCALL_INFO get modified a0 and orig_a0 */
> +				if (ptrace(PTRACE_GETREGSET, pid, NT_PRSTATUS, &iov))
> +					perr_and_exit("failed to get tracee registers");
> +				if (ptrace(PTRACE_GETREGSET, pid, NT_RISCV_ORIG_A0, &a0_iov))
> +					perr_and_exit("failed to get tracee registers");
> +
> +				/* 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");
> +				if (ptrace(PTRACE_SETREGSET, pid, NT_RISCV_ORIG_A0, &a0_iov))
> +					perr_and_exit("failed to set tracee registers");
> +				switch (i) {
> +				case 1:
> +					/* Stop at the beginning of syscall */
> +					rc = ptrace(PTRACE_GET_SYSCALL_INFO, pid,
> +						sizeof(syscall_info), &syscall_info);
> +					if (rc < 0)
> +						perr_and_exit("failed to get syscall info of entry");
> +					if (rc < expected_sci_entry_size
> +						|| syscall_info.op != PTRACE_SYSCALL_INFO_ENTRY)
> +						perr_and_exit("stop position of entry mismatched");
> +					result[0].orig_a0 = syscall_info.entry.args[0];
> +					break;
> +
> +				case 2:
> +					/* Stop at the end of syscall */
> +					rc = ptrace(PTRACE_GET_SYSCALL_INFO, pid,
> +						sizeof(syscall_info), &syscall_info);
> +					if (rc < 0)
> +						perr_and_exit("failed to get syscall info of entry");
> +					if (rc < expected_sci_exit_size
> +						|| syscall_info.op != PTRACE_SYSCALL_INFO_EXIT)
> +						perr_and_exit("stop position of exit mismatched");
> +					result[0].a0 = syscall_info.exit.rval;
> +
> +					if (ptrace(PTRACE_GETREGSET, pid, NT_PRSTATUS, &iov))
> +						perr_and_exit("failed to get tracee registers");
> +					result[1].a0 = regs.a0;
> +					if (ptrace(PTRACE_GETREGSET, pid, NT_RISCV_ORIG_A0,
> +						   &a0_iov))
> +						perr_and_exit("failed to get tracee registers");
> +					result[1].orig_a0 = orig_a0;
> +				}
> +			}
> +			if (ptrace(PTRACE_SYSCALL, pid, 0, 0) < 0)
> +				perr_and_exit("failed to resume tracee");
> +		}
> +	}
> +
> +	/* 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_access_a0)
> +{
> +	struct a0_regs result[2];
> +
> +	ptrace_test(A0_MODIFY, result);
> +
> +	/* Verify PTRACE_SETREGSET */
> +	/* The modification of a0 cannot affect the first argument of the syscall */
> +	EXPECT_EQ(A0_OLD, result[0].orig_a0);
> +	EXPECT_EQ(A0_NEW, result[0].a0);
> +
> +	/* Verify PTRACE_GETREGSET */
> +	EXPECT_EQ(result[1].orig_a0, result[0].orig_a0);
> +	EXPECT_EQ(result[1].a0, result[0].a0);
> +}
> +
> +TEST(ptrace_access_orig_a0)
> +{
> +	struct a0_regs result[2];
> +
> +	ptrace_test(ORIG_A0_MODIFY, result);
> +
> +	/* Verify PTRACE_SETREGSET */
> +	/* Only modify orig_a0 to change the first argument of the syscall */
> +	EXPECT_EQ(A0_NEW, result[0].orig_a0);
> +	/* a0 will keep default value, orig_a0 or -ENOSYS, depends on internal. */
> +	EXPECT_NE(A0_NEW, result[0].a0);

I don't understand this test. Why don't we know what to expect? Also, the
comment says orig_a0 is an option for the value, but then we don't expect
it to be A0_NEW, even though we expect orig_a0 to be A0_NEW?

> +
> +	/* Verify PTRACE_GETREGSET */
> +	EXPECT_EQ(result[1].orig_a0, result[0].orig_a0);
> +	EXPECT_EQ(result[1].a0, result[0].a0);
> +}
> +
> +TEST_HARNESS_MAIN
> 
> -- 
> 2.48.0
>

Other than the two comments/questions, this test looks great.

Thanks,
drew

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