Messages in this thread | | | Subject | Re: Is this a kernel BUG? ///Re: [Question] Can we use SIGRTMIN when vdso disabled on X86? | From | "Leizhen (ThunderTown)" <> | Date | Thu, 7 Jun 2018 11:10:04 +0800 |
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On 2018/6/7 10:39, Andy Lutomirski wrote: > > >> On Jun 6, 2018, at 7:05 PM, Leizhen (ThunderTown) <thunder.leizhen@huawei.com> wrote: >> >> >> >>> On 2018/6/7 1:01, Andy Lutomirski wrote: >>> On Wed, Jun 6, 2018 at 2:18 AM Leizhen (ThunderTown) >>> <thunder.leizhen@huawei.com> wrote: >>>> >>>> I found that glibc has already dealt with this case. So this issue must have been met before, should it be maintained by libc/user? >>>> >>>> if (GLRO(dl_sysinfo_dso) == NULL) >>>> { >>>> kact.sa_flags |= SA_RESTORER; >>>> >>>> kact.sa_restorer = ((act->sa_flags & SA_SIGINFO) >>>> ? &restore_rt : &restore); >>>> } >>>> >>>> >>>>> On 2018/6/6 15:52, Leizhen (ThunderTown) wrote: >>>>> >>>>> >>>>>> On 2018/6/5 19:24, Leizhen (ThunderTown) wrote: >>>>>> After I executed "echo 0 > /proc/sys/abi/vsyscall32" to disable vdso, the rt_sigaction01 test case from ltp_2015 failed. >>>>>> The test case source code please refer to the attachment, and the output as blow: >>>>>> >>>>>> ----------------- >>>>>> ./rt_sigaction01 >>>>>> rt_sigaction01 0 TINFO : signal: 34 >>>>>> rt_sigaction01 1 TPASS : rt_sigaction call succeeded: result = 0 >>>>>> rt_sigaction01 0 TINFO : sa.sa_flags = SA_RESETHAND|SA_SIGINFO >>>>>> rt_sigaction01 0 TINFO : Signal Handler Called with signal number 34 >>>>>> >>>>>> Segmentation fault >>>>>> ------------------ >>>>>> >>>>>> >>>>>> Is this the desired result? In function ia32_setup_rt_frame, I found below code: >>>>>> >>>>>> if (ksig->ka.sa.sa_flags & SA_RESTORER) >>>>>> restorer = ksig->ka.sa.sa_restorer; >>>>>> else >>>>>> restorer = current->mm->context.vdso + >>>>>> vdso_image_32.sym___kernel_rt_sigreturn; >>>>>> put_user_ex(ptr_to_compat(restorer), &frame->pretcode); >>>>>> >>>>>> Because the vdso is disabled, so current->mm->context.vdso is NULL, which cause the result of frame->pretcode invalid. >>>>>> >>>>>> I'm not sure whether this is a kernel bug or just an error of test case itself. Can anyone help me? >>>>>> >>>>> >>>> >>>> >>> >>> I can't tell from your email what you're testing, what behavior you >>> expect, and what you saw. A program that sets up a signal handler >>> without supplying a restorer will not work if the vDSO is off, and >>> this is by design. >> OK, so that the user should take care whether the vDSO is disabled by itself or not, and use different strategies to process it appropriately, like glibc. >> >>> >>> (FWIW, there is a very longstanding libc bug that causes this case to >>> get severely screwed up if the user's SS is not the expected value, >>> and that bug was just fixed very recently. But I doubt this is what >>> you're seeing.) >>> >>> I suppose we could improve the kernel to at least push NULL instead of >>> some random address a bit above 0, but it'll still crash. >> Should we add a warning? Which may help the user to aware this error in time. >> > > It’s entirely valid to have a non working restorer if you never plan to return from a signal handler. And anyone who writes their own libc should be able to figure this out on their own, I think.
OK. Thanks a lot.
> >>> >>> . >>> >> >> -- >> Thanks! >> BestRegards >> > > . >
-- Thanks! BestRegards
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