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From:   ebiederm@xmission.com (Eric W. Biederman)
To:     Arnd Bergmann <arnd@arndb.de>
Cc:     christian@brauner.io, Andy Lutomirski <luto@amacapital.net>,
        Andy Lutomirski <luto@kernel.org>,
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Date:   Sat, 01 Dec 2018 09:28:47 -0600
In-Reply-To: <87y399s3sc.fsf@xmission.com> (Eric W. Biederman's message of
        "Sat, 01 Dec 2018 08:46:43 -0600")
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Subject: Re: [PATCH v2] signal: add procfd_signal() syscall
Sender: linux-kernel-owner@vger.kernel.org
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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.  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.

Eric