linux-kernel - Re: [PATCH v2] signal: add procfd

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Message-ID: <DCA81C46-30A4-4B6A-AA1F-9DCC102968C9@brauner.io>
Date:   Sat, 01 Dec 2018 10:57:11 +1300
From:   Christian Brauner <christian@...uner.io>
To:     Andy Lutomirski <luto@...nel.org>, Arnd Bergmann <arnd@...db.de>
CC:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Andrew Lutomirski <luto@...nel.org>,
        Florian Weimer <fweimer@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "Serge E. Hallyn" <serge@...lyn.com>, Jann Horn <jannh@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Aleksa Sarai <cyphar@...har.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Daniel Colascione <dancol@...gle.com>,
        Tim Murray <timmurray@...gle.com>,
        linux-man <linux-man@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH v2] signal: add procfd_signal() syscall

On December 1, 2018 5:35:45 AM GMT+13:00, Andy Lutomirski <luto@...nel.org> wrote:
>On Fri, Nov 30, 2018 at 3:41 AM Arnd Bergmann <arnd@...db.de> wrote:
>> siginfo_t as it is now still has a number of other downsides, and
>Andy in
>> particular didn't like the idea of having three new variants on x86
>> (depending on how you count). His alternative suggestion of having
>> a single syscall entry point that takes a 'signfo_t __user *' but
>interprets
>> it as compat_siginfo depending on
>in_compat_syscall()/in_x32_syscall()
>> should work correctly, but feels wrong to me, or at least
>inconsistent
>> with how we do this elsewhere.
>
>If everyone else is okay with it, I can get on board with three
>variants on x86.  What I can't get on board with is *five* variants on

Thanks Andy, that helps a lot.
I'm okay with it. Does this require any additional changes to how the syscall
is currently hooked up?

>x86, which would be:
>
>procfd_signal via int80 / the 32-bit vDSO: the ia32 structure
>
>syscall64 with nr == 335 (presumably): 64-bit
>
>syscall64 with nr == 548 | 0x40000000: x32
>
>syscall64 with nr == 548: 64-bit entry but in_compat_syscall() ==
>true, behavior is arbitrary
>
>syscall64 with nr == 335 | 0x40000000: x32 entry, but
>in_compat_syscall() == false, behavior is arbitrary
>
>This mess isn't really Christian's fault -- it's been there for a
>while, but it's awful and I don't think we want to perpetuate it.
>
>Obviously, I'd prefer a variant where the structure that's passed in
>is always the same.
>
>BTW, do we consider siginfo_t to be extensible?  If so, and if we pass

I would prefer if we could consider it extensible.
If so I would prefer if we could pass in a size argument.

>in a pointer, presumably we should pass a length as well.