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Date: Tue, 26 May 2020 06:33:18 -0700 From: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com> To: Andreas Rammhold <andi@...much.email> Cc: Brendan Shanks <bshanks@...eweavers.com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>, "Eric W. Biederman" <ebiederm@...ssion.com>, Sergey Senozhatsky <sergey.senozhatsky@...il.com>, Babu Moger <Babu.Moger@....com>, Kefeng Wang <wangkefeng.wang@...wei.com>, Jason Yan <yanaijie@...wei.com>, linux-kernel@...r.kernel.org Subject: Re: umip: AMD Ryzen 3900X, pagefault after emulate SLDT/SIDT instruction 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 and BR, Ricardo
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