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Subject: Re: [PATCH v2] signal: add procfd_signal() syscall
From:   Andy Lutomirski <luto@amacapital.net>
In-Reply-To: <87tvjxp8pc.fsf@xmission.com>
Date:   Sat, 1 Dec 2018 07:52:37 -0800
Cc:     Arnd Bergmann <arnd@arndb.de>, christian@brauner.io,
        Andy Lutomirski <luto@kernel.org>,
        Florian Weimer <fweimer@redhat.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "Serge E. Hallyn" <serge@hallyn.com>, Jann Horn <jannh@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>, cyphar@cyphar.com,
        Al Viro <viro@zeniv.linux.org.uk>,
        Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>,
        Linux API <linux-api@vger.kernel.org>,
        Daniel Colascione <dancol@google.com>,
        Tim Murray <timmurray@google.com>, linux-man@vger.kernel.org,
        Kees Cook <keescook@chromium.org>
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To:     "Eric W. Biederman" <ebiederm@xmission.com>
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> On Dec 1, 2018, at 7:28 AM, Eric W. Biederman <ebiederm@xmission.com> wrot=
e:
>=20
>=20
> It just occurs to me that the simple way to implement
> procfd_sigqueueinfo info is like:
>=20
> int copy_siginfo_from_user_any(kernel_siginfo_t *info, siginfo_t *uinfo)
> {
> #ifdef CONFIG_COMPAT
>    if (in_compat_syscall)
>        return copy_siginfo_from_user32(info, uinfo);
> #endif
>    return copy_siginfo_from_user(info, uinfo);                       =20
> }
>=20
> long procfd_sigqueueinfo(int fd, siginfo_t *uinfo)
> {
>    kernel_siginfo info;
>=20
>        if (copy_siginfo_from_user_any(&info, uinfo))
>            return -EFAULT;
>    ...;               =20
> }
>=20
> It looks like there is already a place in ptrace.c that already
> hand rolls copy_siginfo_from_user_any.
>=20
> So while I would love to figure out the subset of siginfo_t tha we can
> just pass through, as I think that would make a better more forward
> compatible copy_siginfo_from_user32.

Seems reasonable to me. It=E2=80=99s less code overall than any other sugges=
tion, too.

>  I think for this use case we just
> add the in_compat_syscall test and then we just need to ensure this new
> system call is placed in the proper places in the syscall table.
>=20
> Because we will need 3 call sights: x86_64, x32 and ia32.  As the layout
> changes between those three subarchitecuters.
>=20
>=20

If it=E2=80=99s done this way, it can just be =E2=80=9Ccommon=E2=80=9D in th=
e 64-bit table. And we kick the can a bit farther down the road :)

I=E2=80=99m working on patches to clean up x86=E2=80=99s syscall mess. It=E2=
=80=99s slow because I keep finding new messes.  So far I have rt_sigreturn w=
orking like every other syscall =E2=80=94 whee.

Also, Eric, for your edification, I have a draft patch set to radically simp=
lify x86=E2=80=99s signal delivery and return.  Once that=E2=80=99s done, I c=
an trivially speed up delivery by a ton by using sysret.