[PATCH] selftests/ptrace: Add PTRACE_SYSEMU_SINGLESTEP syscall-exit-stop test

[Oleg Nesterov]

On 09/22, Kees Cook wrote:
>
> ptrace(2) states that no syscall-exit-stop occurs when a tracee is
> continued with PTRACE_SYSEMU or PTRACE_SYSEMU_SINGLESTEP. arm64 gated
> its syscall-exit report on
>
> 	flags & (_TIF_SYSCALL_TRACE | _TIF_SINGLESTEP)
>
> and ptrace_resume() clears SYSCALL_TRACE for both SYSEMU requests while
> PTRACE_SYSEMU_SINGLESTEP additionally sets TIF_SINGLESTEP, so the
> single-step bit alone produced a stop that must not exist. Nothing in
> tools/testing/selftests covered this.

IOW, this test-case veirifies that in the sequence like the generic code

	step = report_single_step(work);
	if (step || work & SYSCALL_WORK_SYSCALL_TRACE)
		arch_ptrace_report_syscall_exit(regs, step);

report_single_step() returns false, right? SYSCALL_TRACE is cleared by
the arch neutral code...

> Link: https://lore.kernel.org/all/20260922035510.1090299-2-ruanjinjie@huawei.com/ [1]
> Assisted-by: LLM
> Signed-off-by: Kees Cook <kees at kernel.org>
> ---
>  tools/testing/selftests/ptrace/Makefile       |   3 +-
>  .../selftests/ptrace/sysemu_singlestep.c      | 176 ++++++++++++++++++
>  tools/testing/selftests/ptrace/.gitignore     |   1 +
>  3 files changed, 179 insertions(+), 1 deletion(-)
>  create mode 100644 tools/testing/selftests/ptrace/sysemu_singlestep.c

Reviewed-by: Oleg Nesterov <oleg at redhat.com>