linux-kernel - Re: [PATCH] uprobes/x86: fix detection of 32-bit user mode

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Date:   Sat, 24 Aug 2019 02:03:08 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Andy Lutomirski <luto@...capital.net>
cc:     Sebastian Mayr <me@....st>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Dmitry Safonov <dsafonov@...tuozzo.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Subject: Re: [PATCH] uprobes/x86: fix detection of 32-bit user mode

On Sat, 24 Aug 2019, Thomas Gleixner wrote:
> On Fri, 23 Aug 2019, Andy Lutomirski wrote:
> > > On Aug 23, 2019, at 4:44 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
> > > 
> > >> On Sat, 24 Aug 2019, Thomas Gleixner wrote:
> > >>> On Sun, 28 Jul 2019, Sebastian Mayr wrote:
> > >>> 
> > >>> -static inline int sizeof_long(void)
> > >>> +static inline int sizeof_long(struct pt_regs *regs)
> > >>> {
> > >>> -    return in_ia32_syscall() ? 4 : 8;
> > >> 
> > >>  This wants a comment.
> > >> 
> > >>> +    return user_64bit_mode(regs) ? 8 : 4;
> > > 
> > > The more simpler one liner is to check
> > > 
> > >    test_thread_flag(TIF_IA32)
> > 
> > I still want to finish killing TIF_IA32 some day.  Let’s please not add new users.
> 
> Well, yes and no. This needs to be backported ....

And TBH the magic in user_64bit_mode() is not pretty either.

Thanks,

	tglx