Messages in this thread | | | From | (Eric W. Biederman) | Date | Wed, 11 Apr 2018 11:11:35 -0500 | Subject | Q: Do si_time and si_utime need to be 64bit for y2038? |
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Arnd,
I am looking at the siginfo si_utime and si_stime fields of type clock_t on 32bit architectures except for x32 these are 32bit fields. For y2038 do we want to extend these fields to 64bit like x32 does? Or is it not a problem for these fields to be 32bit?
I care right now because I am trying to figure out how copy_siginfo_to_user32 and copy_siginfo_to_user need to evolve.
If we are going to extend existing architectures with 64bit variations of si_utime and si_stime copy_siginfo_to_user and copy_siginfo_to_user32 needs an additional parameter describing which variant they should be copying.
It looks like posix does not define si_stime and and si_utime so we only have to be backwards compatible with ourselves for whatever that is worth.
I am wondering if perhaps the general solution might be to just add two extra fields si_stime64 and si_utime64 and always fill those in.
Arnd do you have any ideas?
Andy Lutomirski <luto@amacapital.net> writes:
>> On Apr 10, 2018, at 6:26 PM, Eric W. Biederman <ebiederm@xmission.com> wrote: >> >> >> Andy, >> >> I am looking at copy_siginfo_to_user32 and find it very unfortunate >> that x86 with _sigchld_x32 needs to be the odd man out. I am looking >> at ways to simplify the special case. >> >> The core of the special case comes from: >> exit_to_usermode_loop >> do_signal >> handle_signal >> setup_rt_frame >> >> >> In setup_rt_frame the code looks at ksig to see which kind of signal >> frame should be written for the signal. >> >> This leads to the one case in the kernel where copy_siginfo_to_user32 >> does not use is_ia32_syscall() or is_x32_syscall() to see which kind of >> signal frame it needs to create. >> >> Andy, since you have been all over the entry point code in recent years >> do you know if we allow tasks that can do both ia32 and x86_64 system >> calls? That seems to be what we the testing of ksig to see which kind >> of signal frame to setup is all about. > > We do :( > >> If we don't allow mixed abi's on x86_64 then can I see if I have a ia32 >> task in setup_rt_frame by just calling is_ia32_syscall()? >> >> If we do allow mixed abi's do you know if it would be safe to >> temporarily play with orig_ax or current_thread_info()->status? > > Maybe, but it’s a real minefield. I think the right fix is to use > sa_flags's SA_X32_ABI bit instead for the sigchld bit. In general, > the is_..._syscall() helpers can't be expected to return anything > valid in any context other than a syscall, and handle_signal() is not > a syscall. > >> >> My goal is to write two wrappers: copy_siginfo_to_user32_ia32, and >> copy_siginfo_to_user32_x32 around the ordinary copy_siginfo_to_user32. >> With only a runtime test to see which ABI we need to implement. >> >> Aka change: >>> case SIL_CHLD: >>> to->si_pid = from->si_pid; >>> to->si_uid = from->si_uid; >>> to->si_status = from->si_status; >>> #ifdef CONFIG_X86_X32_ABI >>> if (x32_ABI) { >>> to->_sifields._sigchld_x32._utime = from->si_utime; >>> to->_sifields._sigchld_x32._stime = from->si_stime; >>> } else >>> #endif >>> { >>> to->si_utime = from->si_utime; >>> to->si_stime = from->si_stime; >>> } >>> break; >> to something like: >>> case SIL_CHLD: >>> to->si_pid = from->si_pid; >>> to->si_uid = from->si_uid; >>> to->si_status = from->si_status; >>> #ifdef CONFIG_X86_X32_ABI >>> if (!is_ia32_syscall()) { >>> to->_sifields._sigchld_x32._utime = from->si_utime; >>> to->_sifields._sigchld_x32._stime = from->si_stime; >>> } else >>> #endif >>> { >>> to->si_utime = from->si_utime; >>> to->si_stime = from->si_stime; >>> } >>> break; >> > > Makes sense, but can you get to sa_flags in there instead?
Almost. copy_siginfo_to_user32 is called in 3 places: setup_rt_frame32 (or whatever the arch names the function for setting up the 32bit signal frame), ptrace, and compat_binfmt_elf.
So except for ptrace and compat_binfmt_elf sa_flags are available so that is a possibility. And for those we can fake something up if needed.
Stepping back it really looks like the question is really do we want/need 64bit time in siginfo for 32bit architectures to make the code y2038 safe?
If so passing an extra parameter to copy_siginfo_to_user32 and copy_siginfo_to_user is a no-brainer. If not we are at x86 and in particular x32 is weird. So I am asking Arnd above if he has any idea which way things should evolve.
> FWIW, I have a branch here: > > https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/log/?h=execve > > that contains a *massive* cleanup of some other x86 signal stuff. I > need to dust it off and test it better.
It looks interesting, and except for the last patch "Drop the separate compat signal delivery code" looks orthogonal to what I am doing.
What I have seen other architectures do in that last case are instead of #ifdefs to #define functions to their compat counterparts on 64bit. Something like: #define copy_siginfo_to_user copy_siginfo_to_user32
Eric
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