Dave Martin <Dave.Martin@xxxxxxx> writes:
> On Mon, Jan 15, 2018 at 11:23:03AM -0600, Eric W. Biederman wrote:
>> Dave Martin <Dave.Martin@xxxxxxx> writes:
>>
>> > On Thu, Jan 11, 2018 at 06:59:36PM -0600, Eric W. Biederman wrote:
>
> [...]
>
>> >> Possible ABI fixes include:
>> >> - Send the signal without siginfo
>> >> - Don't generate a signal
>
> [...]
>
>> >> - Possibly assign and use an appropriate si_code
>> >> - Don't handle cases which can't happen
>> >
>> > I think a mixture of these two is the best approach.
>> >
>> > In any case, si_code == 0 here doesn't seem to have any explicit meaning.
>> > I think we can translate all of the arm64 faults to proper si_codes --
>> > see my sketch below. Probably means a bit more thought though.
>
> [...]
>
>> >> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
>
> [...]
>
>> >> @@ -607,70 +607,70 @@ static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs)
>> >> }
>> >>
>> >> static const struct fault_info fault_info[] = {
>> >> - { do_bad, SIGBUS, 0, "ttbr address size fault" },
>> >> - { do_bad, SIGBUS, 0, "level 1 address size fault" },
>> >> - { do_bad, SIGBUS, 0, "level 2 address size fault" },
>> >> - { do_bad, SIGBUS, 0, "level 3 address size fault" },
>
> If I convert this kind of thing to SIGKILL there really is nothing
> sensible to put in si_code, except possibly SI_KERNEL (indicating that
> the kill did not come from userspace). Even so, it hardly seems worth
> filling in fields like si_pid and si_uid just to make this "correct".
>
> In any case, if siginfo is never seen by userspace for SIGKILL this is
> moot.
>
> Obviously, siginfo is never copied to the user stack in that case, but
> is it also guaranteed not to be visible to userspace by other means?
> For ptrace I'm hoping not, since SIGKILL should nuke the tracee
> immediately instead of being reported to the tracer as a
> signal-delivery-stop -- so the tracer should get WIFSIGNALED() &&
> WTERMSIG() == SIGKILL. A subsequent PTRACE_GETSIGINFO would fail with
> ESRCH.
>
> Does that match your understanding?
>
> If so, there is some merit in not pretending to pass a reall value
> for si_code.
>
> Should si_code simply be ignored for the SIGKILL case?
I know what x86 does in a similar case is it uses force_sig instead of
force_sig_info. Then the generic code gets to worry about
If the appropriate paths generic paths get to worry about what siginfo
to fill in in that case. Which for SI_KERNEL is zero for everything
except the si_code and the si_signo.
That seems perfectly reasonable.
Eric
