linux-kernel - Re: [PATCH 4/6] powerpc: use common ptrace_syscall_enter hook to handle _TIF_SYSCALL

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Date:   Mon, 4 Mar 2019 09:36:27 +0000
From:   "Haibo Xu (Arm Technology China)" <Haibo.Xu@....com>
To:     Sudeep Holla <Sudeep.Holla@....com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
CC:     Catalin Marinas <Catalin.Marinas@....com>,
        Will Deacon <Will.Deacon@....com>,
        Oleg Nesterov <oleg@...hat.com>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Richard Weinberger <richard@....at>,
        "jdike@...toit.com" <jdike@...toit.com>,
        Steve Capper <Steve.Capper@....com>,
        "Bin Lu (Arm Technology China)" <Bin.Lu@....com>
Subject: Re: [PATCH 4/6] powerpc: use common ptrace_syscall_enter hook to
 handle _TIF_SYSCALL_EMU

On 2019/3/1 2:32, Sudeep Holla wrote:
> Now that we have a new hook ptrace_syscall_enter that can be called from
> syscall entry code and it handles PTRACE_SYSEMU in generic code, we
> can do some cleanup using the same in do_syscall_trace_enter.
>
> Cc: Oleg Nesterov <oleg@...hat.com>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Signed-off-by: Sudeep Holla <sudeep.holla@....com>
> ---
>  arch/powerpc/kernel/ptrace.c | 50 ++++++++++++++++--------------------
>  1 file changed, 22 insertions(+), 28 deletions(-)
>
> diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
> index cb7e1439cafb..978cd2aac29e 100644
> --- a/arch/powerpc/kernel/ptrace.c
> +++ b/arch/powerpc/kernel/ptrace.c
> @@ -3264,37 +3264,31 @@ long do_syscall_trace_enter(struct pt_regs *regs)
>  {
>  u32 flags;
>
> -user_exit();

We'd better keep the user_exit() at here in case both context tracking and SYSCALL_EMU
are enabled.

> -
> -flags = READ_ONCE(current_thread_info()->flags) &
> -(_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE);
> +if (unlikely(ptrace_syscall_enter(regs))) {
> +/*
> + * 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 registers, so we don't goto the skip
> + * label below.
> + */
> +return -1;
> +}
>
> -if (flags) {
> -int rc = tracehook_report_syscall_entry(regs);
> +user_exit();
>
> -if (unlikely(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 registers, so we don't goto
> - * the skip label below.
> - */
> -return -1;
> -}
> +flags = READ_ONCE(current_thread_info()->flags) & _TIF_SYSCALL_TRACE;
>
> -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;
> -}
> +if (flags && tracehook_report_syscall_entry(regs)) {
> +/*
> + * 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]. */
>
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