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SubjectRe: [PATCH v6] powerpc/ptrace: replace ptrace_report_syscall() with a tracehook call
On 12/07, Dmitry V. Levin wrote:
>
> Please make either v5 or v6 edition of this fix, or any similar fix,
> into v4.20.

IIUC, v5 above means

[PATCH v5 23/25] powerpc/ptrace: replace ptrace_report_syscall() with a tracehook call

you sent in another series...

> long do_syscall_trace_enter(struct pt_regs *regs)
> {
> + struct thread_info *ti;
> + u32 cached_flags;
> +
> user_exit();
>
> - if (test_thread_flag(TIF_SYSCALL_EMU)) {
> - ptrace_report_syscall(regs);
> - /*
> - * Returning -1 will skip the syscall execution. We want to
> - * avoid clobbering any register also, thus, not 'gotoing'
> - * skip label.
> - */
> - return -1;
> - }
> + ti = current_thread_info();
> + cached_flags = READ_ONCE(ti->flags) &
> + (_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE |
> + _TIF_SYSCALL_TRACEPOINT);
>
> - /*
> - * The tracer may decide to abort the syscall, if so tracehook
> - * will return !0. Note that the tracer may also just change
> - * regs->gpr[0] to an invalid syscall number, that is handled
> - * below on the exit path.
> - */
> - if (test_thread_flag(TIF_SYSCALL_TRACE) &&
> - tracehook_report_syscall_entry(regs))
> - goto skip;
> + if (cached_flags & (_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE)) {
> + int rc = tracehook_report_syscall_entry(regs);
> +
> + if (unlikely(cached_flags & _TIF_SYSCALL_EMU)) {
> + /*
> + * A nonzero return code from
> + * tracehook_report_syscall_entry() tells us
> + * to prevent the syscall execution, but
> + * we are not going to execute it anyway.
> + *
> + * Returning -1 will skip the syscall execution.
> + * We want to avoid clobbering any register also,
> + * thus, not 'gotoing' skip label.
> + */
> + return -1;
> + }
> +
> + if (rc) {
> + /*
> + * The tracer decided to abort the syscall.
> + * Note that the tracer may also just change
> + * regs->gpr[0] to an invalid syscall number,
> + * that is handled below on the exit path.
> + */
> + goto skip;
> + }
> + }
>
> /* Run seccomp after ptrace; allow it to set gpr[3]. */
> if (do_seccomp(regs))
> @@ -3293,7 +3309,7 @@ long do_syscall_trace_enter(struct pt_regs *regs)
> if (regs->gpr[0] >= NR_syscalls)
> goto skip;
>
> - if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
> + if (unlikely(cached_flags & _TIF_SYSCALL_TRACEPOINT))

I will leave this to maintainers, but to me this change looks good and imo it
also cleanups the code.

However I am not sure cached_flags should include _TIF_SYSCALL_TRACEPOINT. If
nothing else, the caller can sleep in ptrace_stop() unpredictably long and
TIF_SYSCALL_TRACEPOINT can be set/cleared meanwhile.

Oleg.

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