On Sat, Dec 1, 2018 at 12:54 AM Andy Lutomirski [off-list ref] wrote:

On Fri, Nov 30, 2018 at 2:10 PM Arnd Bergmann [off-list ref] wrote:

quoted

On Fri, Nov 30, 2018 at 5:36 PM Andy Lutomirski [off-list ref] wrote:

quoted

On Fri, Nov 30, 2018 at 3:41 AM Arnd Bergmann [off-list ref] wrote:

quoted

siginfo_t as it is now still has a number of other downsides, and Andy in
particular didn't like the idea of having three new variants on x86
(depending on how you count). His alternative suggestion of having
a single syscall entry point that takes a 'signfo_t __user *' but interprets
it as compat_siginfo depending on in_compat_syscall()/in_x32_syscall()
should work correctly, but feels wrong to me, or at least inconsistent
with how we do this elsewhere.

quoted

The '548 | 0x40000000' part seems to be the only sensible
way to handle x32 here. What exactly would you propose to
avoid defining the other entry points?

I would propose that it should be 335 | 0x40000000.  I can't see any
reasonable way to teach the kernel to reject 335 | 0x40000000 that
wouldn't work just as well to accept it and make it do the right
thing.  Currently we accept it and do the *wrong* thing, which is no
good.

quoted

and we have to
add more complexity to the copy_siginfo_from_user()
implementation to duplicate the hack that exists in
copy_siginfo_from_user32().

What hack are you referring to here?

I mean this part:

#ifdef CONFIG_COMPAT
int copy_siginfo_to_user32(struct compat_siginfo __user *to,
                           const struct kernel_siginfo *from)
#if defined(CONFIG_X86_X32_ABI) || defined(CONFIG_IA32_EMULATION)
{
        return __copy_siginfo_to_user32(to, from, in_x32_syscall());
}
int __copy_siginfo_to_user32(struct compat_siginfo __user *to,
                             const struct kernel_siginfo *from, bool x32_ABI)
#endif
{
...
        case SIL_CHLD:
                new.si_pid    = from->si_pid;
                new.si_uid    = from->si_uid;
                new.si_status = from->si_status;
#ifdef CONFIG_X86_X32_ABI
                if (x32_ABI) {
                        new._sifields._sigchld_x32._utime = from->si_utime;
                        new._sifields._sigchld_x32._stime = from->si_stime;
                } else
#endif
                {
                        new.si_utime = from->si_utime;
                        new.si_stime = from->si_stime;
                }
                break;
...
}
#endif

If we have a '548 | 0x40000000' entry pointing to
__x32_compat_sys_procfd_kill, then that will do the right
thing. If you instead try to have x32 call into the native
sys_procfd_kill, then copy_siginfo_to_user() will also have
to know about x32, effectively duplicating that mess above,
unless you want to also change all users of
copy_siginfo_to_user32() to use copy_siginfo_to_user()
and handle all cases in one function.

        Arnd