On 06:33 26.05.20, Ricardo Neri wrote: > On Sat, May 23, 2020 at 04:17:39AM +0200, Andreas Rammhold wrote: > > On 12:43 19.05.20, Ricardo Neri wrote: > > > I have a patch for this already that I wrote for testing purposes: > > > https://github.com/ricardon/tip/commit/1692889cb3f8accb523d44b682458e234b93be50 > > > Perhaps it can be used as a starting point? Not sure what the spoofing > > > value should be, though. Perhaps 0? > > > > I tried the above patch (in modified/rebased version; hope that didn't > > kill it [0]). The results are negative, as without the patch. > > Ah. My patch above is based on a rather old kernel. There is a check in > fixup_umip_exception() for SLDT and STR. I think this causes the > exception you see. Perhaps you can try by removing such check: > > diff --git a/arch/x86/kernel/umip.c b/arch/x86/kernel/umip.c > @@ -383,10 +389,6 @@ bool fixup_umip_exception(struct pt_regs *regs) > umip_pr_warn(regs, "%s instruction cannot be used by applications.\n", > umip_insns[umip_inst]); > > - /* Do not emulate (spoof) SLDT or STR. */ > - if (umip_inst == UMIP_INST_STR || umip_inst == UMIP_INST_SLDT) > - return false; > - > umip_pr_warn(regs, "For now, expensive software emulation returns the > result.\n"); > > if (emulate_umip_insn(&insn, umip_inst, dummy_data, &dummy_data_size, > > You would still need my old patch.
Thanks, that works for my application. Regards, Andi
