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

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Message-Id: <F53D6D38-3521-4C20-9034-5AF447DF62FF@amacapital.net>
Date:   Sat, 1 Dec 2018 07:52:37 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Arnd Bergmann <arnd@...db.de>, christian@...uner.io,
        Andy Lutomirski <luto@...nel.org>,
        Florian Weimer <fweimer@...hat.com>,
        Linux Kernel Mailing List <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>, cyphar@...har.com,
        Al Viro <viro@...iv.linux.org.uk>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Daniel Colascione <dancol@...gle.com>,
        Tim Murray <timmurray@...gle.com>, linux-man@...r.kernel.org,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH v2] signal: add procfd_signal() syscall



> On Dec 1, 2018, at 7:28 AM, Eric W. Biederman <ebiederm@...ssion.com> wrote:
> 
> 
> It just occurs to me that the simple way to implement
> procfd_sigqueueinfo info is like:
> 
> 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);                        
> }
> 
> long procfd_sigqueueinfo(int fd, siginfo_t *uinfo)
> {
>    kernel_siginfo info;
> 
>        if (copy_siginfo_from_user_any(&info, uinfo))
>            return -EFAULT;
>    ...;                
> }
> 
> It looks like there is already a place in ptrace.c that already
> hand rolls copy_siginfo_from_user_any.
> 
> 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’s less code overall than any other suggestion, 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.
> 
> Because we will need 3 call sights: x86_64, x32 and ia32.  As the layout
> changes between those three subarchitecuters.
> 
> 

If it’s done this way, it can just be “common” in the 64-bit table. And we kick the can a bit farther down the road :)

I’m working on patches to clean up x86’s syscall mess. It’s slow because I keep finding new messes.  So far I have rt_sigreturn working like every other syscall — whee.

Also, Eric, for your edification, I have a draft patch set to radically simplify x86’s signal delivery and return.  Once that’s done, I can trivially speed up delivery by a ton by using sysret.