linux-kernel - Re: [5.2 REGRESSION] Generic vDSO breaks seccomp-enabled userspace on i386

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Date:   Sun, 28 Jul 2019 20:16:55 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Arnd Bergmann <arnd@...db.de>
cc:     Andy Lutomirski <luto@...nel.org>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Kees Cook <keescook@...omium.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
        Paul Bolle <pebolle@...cali.nl>
Subject: Re: [5.2 REGRESSION] Generic vDSO breaks seccomp-enabled userspace
 on i386

On Sun, 28 Jul 2019, Thomas Gleixner wrote:
> On Sun, 28 Jul 2019, Arnd Bergmann wrote:
> 
> > On Sun, Jul 28, 2019 at 12:30 PM Thomas Gleixner <tglx@...utronix.de> wrote:
> > > On Sun, 28 Jul 2019, Arnd Bergmann wrote:
> > > > On Sat, Jul 27, 2019 at 7:53 PM Andy Lutomirski <luto@...nel.org> wrote:
> > 
> > > Which is totally irrelevant because res is NULL and that NULL pointer check
> > > should simply return -EFAULT, which is what the syscall fallback returns
> > > because the pointer is NULL.
> > >
> > > But that NULL pointer check is inconsistent anyway:
> > >
> > >  - 64 bit does not have it and never had
> > >
> > >  - the vdso is not capable of handling faults properly anyway. If the
> > >    pointer is not valid, then it will segfault. So just preventing the
> > >    segfault for NULL is silly.
> > >
> > > I'm going to just remove it.
> > 
> > Ah, you are right, I misread.
> > 
> > Anyway, if we want to keep the traditional behavior and get fewer surprises
> > for users of seccomp and anything else that might observe clock_gettime
> > behavior, below is how I'd do it. (not even build tested, x86-only. I'll
> > send a proper patch if this is where we want to take it).
> 
> I posted a series which fixes up the mess 2 hours before you sent this mail :)

And stupid me forgot to CC you. I was entirely sure that I did....

   https://lkml.kernel.org/r/20190728131251.622415456@linutronix.de

Sorry

	tglx