Re: [PATCH v5 2/2] riscv: selftests: Add a ptrace test to verify a0 and orig_a0 access

On 2025-01-15 17:14, Andrew Jones wrote:

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@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 | 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.

Agreed. But it may be better to be a separate patchset so we can change those definition in different selftests one pass.

...

+#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?

The purpose of the test is to ensure that the ORIG_A0_MODIFY operation will not affect the a0 register (So it will not be our A0_NEW). But there is a problem with the comment. It is written for some old wrong code. I will correct the comment.

...

• /* 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