On Mon, Dec 02, 2024 at 09:37:04PM -0800, Charlie Jenkins wrote:
[...]
> +static void ptrace_test(int opt, int *result)
> +{
> + int status;
> + pid_t pid;
> + struct user_regs_struct regs;
> + struct iovec iov = {
> + .iov_base = ®s,
> + .iov_len = sizeof(regs),
> + };
> +
> + unsigned long orig_a0;
> + struct iovec a0_iov = {
> + .iov_base = &orig_a0,
> + .iov_len = sizeof(orig_a0),
> + };
> +
> + 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 regs before the syscall */
> + if (ptrace(PTRACE_GETREGSET, pid, NT_PRSTATUS, &iov))
> + perr_and_exit("failed to get tracee registers\n");
> + if (ptrace(PTRACE_GETREGSET, pid, NT_RISCV_ORIG_A0, &a0_iov))
> + perr_and_exit("failed to get tracee registers\n");
> + if (orig_a0 != A0_OLD)
> + perr_and_exit("unexpected orig_a0: 0x%lx\n", orig_a0);
> +
> + /* Modify a0/orig_a0 for the syscall */
> + switch (opt) {
> + case A0_MODIFY:
> + regs.a0 = A0_NEW;
> + break;
Did you mean applying the modified user_regs_struct using PTRACE_SETREGSET?
If yes, then there should be an appropriate PTRACE_SETREGSET NT_PRSTATUS call.
If no, then regs is ignored, so why would you change it in the first place?
> + case ORIG_A0_MODIFY:
> + orig_a0 = A0_NEW;
> + break;
> + }
> +
> + if (ptrace(PTRACE_SETREGSET, pid, NT_RISCV_ORIG_A0, &a0_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);
> +}
--
ldv
