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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Michael Ellerman <mpe@ellerman.id.au>,
        Kees Cook <keescook@chromium.org>
Cc:     Robert O'Callahan <rocallahan@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        "maintainer\:X86 ARCHITECTURE \(32-BIT AND 64-BIT\)" <x86@kernel.org>,
        linux-arch@vger.kernel.org, Will Deacon <will@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Mark Rutland <mark.rutland@arm.com>,
        Keno Fischer <keno@juliacomputing.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        kvm list <kvm@vger.kernel.org>,
        Gabriel Krisman Bertazi <krisman@collabora.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Kyle Huey <me@kylehuey.com>
Subject: Re: [REGRESSION] x86/entry: Tracer no longer has opportunity to change the syscall number at entry via orig_ax
In-Reply-To: <87d02qqfxy.fsf@mpe.ellerman.id.au>
References: <CAP045Arc1Vdh+n2j2ELE3q7XfagLjyqXji9ZD0jqwVB-yuzq-g@mail.gmail.com> <87blj6ifo8.fsf@nanos.tec.linutronix.de> <87a6xzrr89.fsf@mpe.ellerman.id.au> <202009111609.61E7875B3@keescook> <87d02qqfxy.fsf@mpe.ellerman.id.au>
Date:   Sun, 13 Sep 2020 20:27:23 +0200
Message-ID: <87o8m98rck.fsf@nanos.tec.linutronix.de>
MIME-Version: 1.0
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Sender: linux-kernel-owner@vger.kernel.org
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On Sun, Sep 13 2020 at 17:44, Michael Ellerman wrote:
> Kees Cook <keescook@chromium.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