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

Andy Lutomirski [off-list ref] writes:

quoted

On Dec 1, 2018, at 7:28 AM, Eric W. Biederman [off-list ref] 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.

quoted

 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.

Nice.

Do we care about the performance of synchronous signal delivery (AKA
hardware exceptions) vs ordinary signal delivery.  I get the feeling
there are serious simplifications to be had in that case.

Eric