Messages in this thread | | | Subject | Re: Is this a kernel BUG? ///Re: [Question] Can we use SIGRTMIN when vdso disabled on X86? | From | Andy Lutomirski <> | Date | Wed, 6 Jun 2018 19:39:50 -0700 |
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> 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.
>> >> . >> > > -- > Thanks! > BestRegards >
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