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

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Message-Id: <17F255F9-5084-4E30-9AD6-80A4F49BD0D8@amacapital.net>
Date:   Tue, 23 Jul 2019 07:04:46 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [5.2 REGRESSION] Generic vDSO breaks seccomp-enabled userspace on i386



> On Jul 23, 2019, at 2:18 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> 
>> On Mon, Jul 22, 2019 at 04:47:36PM -0700, Andy Lutomirski wrote:
>> 
>> I don't love this whole concept, but I also don't have a better idea.
> 
> Are we really talking about changing the kernel because BPF is expecting
> things? That is, did we just elevate everything BPF can observe to ABI?
> 

No, this isn’t about internals in the kernel mode sense. It’s about the smallish number of cases where the kernel causes user code to do a specific syscall and the user has a policy that doesn’t allow that syscall.  This is visible to user code via seccomp and ptrace.

Yes, it’s obnoxious.  Do you have any suggestions?