Helge Deller <deller@xxxxxx> writes: > On 23.02.2018 01:15, Eric W. Biederman wrote: >> Helge Deller <deller@xxxxxx> writes: >> >>> * Eric W. Biederman <ebiederm@xxxxxxxxxxxx>: >>>> Setting si_code to 0 results in a userspace seeing an si_code of 0. >>>> This is the same si_code as SI_USER. Posix and common sense requires >>>> that SI_USER not be a signal specific si_code. As such this use of 0 >>>> for the si_code is a pretty horribly broken ABI. >>>> >>>> Further use of si_code == 0 guaranteed that copy_siginfo_to_user saw a >>>> value of __SI_KILL and now sees a value of SIL_KILL with the result >>>> that uid and pid fields are copied and which might copying the si_addr >>>> field by accident but certainly not by design. Making this a very >>>> flakey implementation. >>>> >>>> Utilizing FPE_FIXME siginfo_layout will now return SIL_FAULT and the >>>> appropriate fields will reliably be copied. >>>> >>>> This bug is 13 years old and parsic machines are no longer being built >>>> so I don't know if it possible or worth fixing it. But it is at least >>>> worth documenting this so other architectures don't make the same >>>> mistake. >>> >>> >>> I think we should fix it, even if we now break the ABI. >>> >>> It's about a "conditional trap" which needs to be handled by userspace. >>> I doubt there is any Linux code out which is utilizing this >>> parisc-specific trap. >>> >>> I'd suggest to add a new FPE trap si_code (e.g. FPE_CONDTRAP). >>> While at it, maybe we should include the already existing FPE_MDAOVF >>> from the frv architecture, so that arch/frv/include/uapi/asm/siginfo.h >>> can go completely. >>> >>> Suggested patch is below. >>> >>> I'm willing to test the patch below on the parisc architecture for a few >>> weeks. And it will break arch/x86/kernel/signal_compat.c which needs >>> looking at then too. >> >> Have you managed to test this change? > > Sadly I haven't done any further testing yet. So at this point for purposed of testing I don't think it matters which number FPE_CONDTRAP gets as long as it is non-zero. > >> I am sitting looking at another new FPE si_code and if this has been tested >> I figure FPE_CONDTRAP should get the next available FPE si_code and the >> other change should get the one that follows. > > I'm fine either way. Do you have a git tree I can pull which includes > all your patches? I can then start testing. Everything finalized is in Linus's tree. There is a patch pending review on linux-arch that defines FPE_FLTUNK that looks to be useful on several architectures. I had probably misread our earlier exchange. I had hoped you had tested that FPE_CONDTRAP did not cause problems. If that level of testing was complete I would have given FPE_CONDTRAP the next FPE number and FPE_FLTUNK the one after. As it sounds like FPE_CONDTRAP hasn't been tested enough to know if it causes problems I will encourage the patches to be merged in the other order. Eric -- To unsubscribe from this list: send the line "unsubscribe linux-parisc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
