lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Thu, 18 Sep 2014 17:28:08 -0700 From: "H. Peter Anvin" <hpa@...or.com> To: Andy Lutomirski <luto@...capital.net>, Henrique de Moraes Holschuh <hmh@....eng.br> CC: Borislav Petkov <bp@...en8.de>, Chuck Ebbert <cebbert.lkml@...il.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: x86, microcode: BUG: microcode update that changes x86_capability The cpuid bit gets twiddled... On September 18, 2014 5:23:40 PM PDT, Andy Lutomirski <luto@...capital.net> wrote: >On Sep 18, 2014 5:13 PM, "Henrique de Moraes Holschuh" <hmh@....eng.br> >wrote: >> >> On Thu, 18 Sep 2014, Henrique de Moraes Holschuh wrote: >> > On Thu, 18 Sep 2014, H. Peter Anvin wrote: >> > > We should, but this is also part of why we want the early ucode >capability. >> > >> > Well, yes. But that won't help the several stable and LTS distros >with >> > kernels without early ucode update support. >> >> Here's a plan that might work, pending actually checking the >libpthread TSX >> code to make sure it keys on /proc/cpuinfo flags: > >Surely it checks cpuid directly, though. > >Can we twiddle the cpuid bit? I never noticed any way in the docs to >do it, but if BIOS has such an ability, maybe we do, too. I wonder if >there's anything semi-documented in biosbits, or if we could just >reverse-engineer it. > >--Andy > >> >> Add a cpu quirk, triggered by the Haswell cpuids, to force-disable >hle on >> the affected processors. >> >> This will work around the x86_capability capability issue (which >should >> still be fixed, anyway), and it should also get userspace to stay >away from >> TSX, therefore also working around the worst issue (processes getting >> SIGILL). >> >> This will disable the "user may ask the BIOS to keep TSX enabled" >> anti-feature, though. This drawback can be avoided, but only if a >future >> microcode update won't re-disable hle when the BIOS enabled it. For >now, I >> suggest that we decree that "hle is toast" for the current Haswells >and add >> back ways to enable it for testing when we know more about it. >> >> -- >> "One disk to rule them all, One disk to find them. One disk to >bring >> them all and in the darkness grind them. In the Land of Redmond >> where the shadows lie." -- The Silicon Valley Tarot >> Henrique Holschuh -- Sent from my mobile phone. Please pardon brevity and lack of formatting. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists