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Subject: Re: [PATCH v2] signal: add procfd_signal() syscall
To:     Andy Lutomirski <luto@amacapital.net>,
        "Eric W. Biederman" <ebiederm@xmission.com>
CC:     Arnd Bergmann <arnd@arndb.de>, 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>
From:   Christian Brauner <christian@brauner.io>
Message-ID: <7089A038-6685-4EB4-A67A-CE692B32147B@brauner.io>
Sender: linux-kernel-owner@vger.kernel.org
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On December 2, 2018 4:52:37 AM GMT+13:00, Andy Lutomirski <luto@amacapital=
=2Enet> wrote:
>
>
>> On Dec 1, 2018, at 7:28 AM, Eric W=2E Biederman <ebiederm@xmission=2Eco=
m>
>wrote:
>>=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;
>>    =2E=2E=2E;               =20
>> }
>>=20
>> It looks like there is already a place in ptrace=2Ec that already
>> hand rolls copy_siginfo_from_user_any=2E
>>=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=2E
>
>Seems reasonable to me=2E It=E2=80=99s less code overall than any other
>suggestion, too=2E

Thanks everyone, that was super helpful!
All things equal I'm going to send out an
updated version of the patch latest next week!

>
>>  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=2E
>>=20
>> Because we will need 3 call sights: x86_64, x32 and ia32=2E  As the
>layout
>> changes between those three subarchitecuters=2E
>>=20
>>=20
>
>If it=E2=80=99s done this way, it can just be =E2=80=9Ccommon=E2=80=9D in=
 the 64-bit table=2E 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=2E =
It=E2=80=99s slow
>because I keep finding new messes=2E  So far I have rt_sigreturn working
>like every other syscall =E2=80=94 whee=2E
>
>Also, Eric, for your edification, I have a draft patch set to radically
>simplify x86=E2=80=99s signal delivery and return=2E  Once that=E2=80=99s=
 done, I can
>trivially speed up delivery by a ton by using sysret=2E