Re: [PATCH v2] signal: add procfd_signal() syscall

[Andy Lutomirski]

> On Dec 1, 2018, at 7:28 AM, Eric W. Biederman <ebiederm@xxxxxxxxxxxx> 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. Itâs 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 itâs done this way, it can just be âcommonâ in the 64-bit table. And we kick the can a bit farther down the road :)

Iâm working on patches to clean up x86âs syscall mess. Itâs slow because I keep finding new messes.  So far I have rt_sigreturn working like every other syscall â whee.

Also, Eric, for your edification, I have a draft patch set to radically simplify x86âs signal delivery and return.  Once thatâs done, I can trivially speed up delivery by a ton by using sysret.