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
On Sat, Dec 1, 2018 at 4:07 PM Eric W. Biederman [off-list ref] wrote:
Andy Lutomirski [off-list ref] writes:
quoted
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.
I dunno what user code cares about. Linux's support for synchronous
exception handling is so far behind, say, Windows, that I don't know
if it's even used for anything very serious. We should probably
profile it after I finish my changes and we can see how bad it is. We
can't do anything at all about the time it takes the CPU to deliver
the exception, and trying to avoid IRET when we return would be tricky
at best, although siglongjmp() might end up skipping it.