Re: [v6 PATCH 00/21] x86: Enable User-Mode Instruction Prevention
Ricardo Neri writes: > On Fri, 2017-03-31 at 16:11 +0200, Alexandre Julliard wrote: >> Ricardo Neri writes: >> >> > On Thu, 2017-03-30 at 13:10 +0300, Stas Sergeev wrote: >> >> 30.03.2017 08:14, Ricardo Neri пишет: >> >> In fact, smsw has an interesting property, which is that >> >> no one will ever want to disable its in-kernel emulation >> >> to provide its own. >> >> So while I'll try to estimate its usage, emulating it in kernel >> >> will not be that problematic in either case. >> > >> > Ah good to know! >> > >> >> As for protected mode, if wine only needs sgdt/sidt, then >> >> again, no one will want to disable its emulation. Not the >> >> case with sldt, but AFAICS wine doesn't need sldt, and so >> >> we can leave sldt without a fixups. Is my understanding >> >> correct? >> > >> > This is my understanding as well. I could not find any use of sldt in >> > wine. Alexandre, would you mind confirming? >> >> Some versions of the Themida software protection are known to use sldt >> as part of the virtual machine detection code [1]. The check currently >> fails because it expects the LDT to be zero, so the app is already >> broken, but sldt segfaulting would still cause a crash where there >> wasn't one before. >> >> However, I'm only aware of one application using this, and being able to >> catch and emulate sldt ourselves would actually give us a chance to fix >> this app in newer Wine versions, so I'm not opposed to having it >> segfault. > > Great! Then this is in line with what we are aiming to do with dosemu2: > not emulate str and sldt. >> >> In fact it would be nice to be able to make sidt/sgdt/etc. segfault >> too. I know a new syscall is a pain, but as far as Wine is concerned, >> being able to opt out from any emulation would be potentially useful. > > I see. I guess for now there should not be a problem with emulating > sidt/sgdt/smsw, right? In this way we don't break current versions of > winehq and programs using it. In a phase two we can introduce the > syscall so that kernel fixups can be disabled. Does this make sense? Yes, that makes sense. -- Alexandre Julliard julli...@winehq.org -- To unsubscribe from this list: send the line "unsubscribe linux-msdos" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [v6 PATCH 00/21] x86: Enable User-Mode Instruction Prevention
On Sat, 2017-04-01 at 16:08 +0300, Stas Sergeev wrote: > 30.03.2017 08:14, Ricardo Neri пишет: > >> You know the wine's > >> requirements now - they are very small. And > >> dosemu doesn't need anything at all but smsw. > >> And even smsw is very rare. > > But emulation is still needed for SMSW, right? > Likely so. > If you want, I can enable the logging of this command > and see if it is used by some of the DOS programs I have. > >>> It would be great if you could do that, if you don't mind. > >> OK, scheduled to the week-end. > >> I'll let you know. > > Thanks! > OK, done the testing. > It appears smsw is used in v86 by windows-3.1 and dos4gw > at the very least, and these are the "major" apps. So doing > without a fixup in v86 will not go unnoticed. Unfortunately > this also means that KVM-vm86 should be properly tested. > I have also found a weird program that does SGDT under > v86. This causes "ERROR: SGDT not implemented" under > dosemu, but the prog still works fine as it obviously does > not care about the results. This app can easily be broken > of course, if that makes any sense (likely not). Thanks for inputs! Then it seems that we will need emulation for sgdt and smsw. Perhaps sidt? sldt and str will not need emulation in either protected mode or virtual-8086 mode. At a later stage I can look into working in the syscall as Andy proposes. I will also look into the kvm-v86 path for dosemu2. It seems we have an agreement :) Do we? Thanks and BR, Ricardo -- To unsubscribe from this list: send the line "unsubscribe linux-msdos" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [v6 PATCH 00/21] x86: Enable User-Mode Instruction Prevention
On Fri, 2017-03-31 at 16:11 +0200, Alexandre Julliard wrote: > Ricardo Neri writes: > > > On Thu, 2017-03-30 at 13:10 +0300, Stas Sergeev wrote: > >> 30.03.2017 08:14, Ricardo Neri пишет: > >> But at least dosemu implements it, so probably it is needed. > >> >>> Right. > >> >>> > >> Of course if it is used by one of 100 DOS progs, then there > >> is an option to just add its support to dosemu2 and pretend > >> the compatibility problems did not exist. :) > >> >>> Do you mean relaying the GP fault to dosemu instead of trapping it and > >> >>> emulating it in the kernel? > >> >> Yes, that would be optimal if this does not severely break > >> >> the current setups. If we can find out that smsw is not in > >> >> the real use, we can probably do exactly that. > >> >> But other > >> >> instructions are not in real use in v86 for sure, so I > >> >> wouldn't be adding the explicit test-cases to the kernel > >> >> that will make you depend on some particular behaviour > >> >> that no one may need. > >> >> My objection was that we shouldn't > >> >> write tests before we know exactly how we want this to work. > >> > OK, if only SMSW is used then I'll keep the emulation for SMSW only. > >> In fact, smsw has an interesting property, which is that > >> no one will ever want to disable its in-kernel emulation > >> to provide its own. > >> So while I'll try to estimate its usage, emulating it in kernel > >> will not be that problematic in either case. > > > > Ah good to know! > > > >> As for protected mode, if wine only needs sgdt/sidt, then > >> again, no one will want to disable its emulation. Not the > >> case with sldt, but AFAICS wine doesn't need sldt, and so > >> we can leave sldt without a fixups. Is my understanding > >> correct? > > > > This is my understanding as well. I could not find any use of sldt in > > wine. Alexandre, would you mind confirming? > > Some versions of the Themida software protection are known to use sldt > as part of the virtual machine detection code [1]. The check currently > fails because it expects the LDT to be zero, so the app is already > broken, but sldt segfaulting would still cause a crash where there > wasn't one before. > > However, I'm only aware of one application using this, and being able to > catch and emulate sldt ourselves would actually give us a chance to fix > this app in newer Wine versions, so I'm not opposed to having it > segfault. Great! Then this is in line with what we are aiming to do with dosemu2: not emulate str and sldt. > > In fact it would be nice to be able to make sidt/sgdt/etc. segfault > too. I know a new syscall is a pain, but as far as Wine is concerned, > being able to opt out from any emulation would be potentially useful. I see. I guess for now there should not be a problem with emulating sidt/sgdt/smsw, right? In this way we don't break current versions of winehq and programs using it. In a phase two we can introduce the syscall so that kernel fixups can be disabled. Does this make sense? Thanks and BR, Ricardo -- To unsubscribe from this list: send the line "unsubscribe linux-msdos" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
