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

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Message-ID: <202009141303.08B39E5783@keescook>
Date:   Mon, 14 Sep 2020 13:04:06 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        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 08:27:23PM +0200, Thomas Gleixner wrote:
> 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?

I already did on Friday:
https://lore.kernel.org/lkml/20200912005826.586171-1-keescook@chromium.org/

-- 
Kees Cook