linux-kernel - Re: [REGRESSION] x86/entry: Tracer no longer has opportunity to change the syscall number at entry via orig

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Date:   Sun, 13 Sep 2020 20:27:23 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Kees Cook <keescook@...omium.org>
Cc:     Robert O'Callahan <rocallahan@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "maintainer\:X86 ARCHITECTURE \(32-BIT AND 64-BIT\)" <x86@...nel.org>,
        linux-arch@...r.kernel.org, Will Deacon <will@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Mark Rutland <mark.rutland@....com>,
        Keno Fischer <keno@...iacomputing.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        kvm list <kvm@...r.kernel.org>,
        Gabriel Krisman Bertazi <krisman@...labora.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Kyle Huey <me@...ehuey.com>
Subject: Re: [REGRESSION] x86/entry: Tracer no longer has opportunity to change the syscall number at entry via orig_ax

On Sun, Sep 13 2020 at 17:44, Michael Ellerman wrote:
> Kees Cook <keescook@...omium.org> writes:
> diff --git a/kernel/entry/common.c b/kernel/entry/common.c
> index 18683598edbc..901361e2f8ea 100644
> --- a/kernel/entry/common.c
> +++ b/kernel/entry/common.c
> @@ -60,13 +60,15 @@ static long syscall_trace_enter(struct pt_regs *regs, long syscall,
>                         return ret;
>         }
>  
> +       syscall = syscall_get_nr(current, regs);
> +
>         if (unlikely(ti_work & _TIF_SYSCALL_TRACEPOINT))
>                 trace_sys_enter(regs, syscall);
>  
>         syscall_enter_audit(regs, syscall);
>  
>         /* The above might have changed the syscall number */
> -       return ret ? : syscall_get_nr(current, regs);
> +       return ret ? : syscall;
>  }

Yup, this looks right. Can you please send a proper patch?

Thanks,

        tglx