Messages in this thread | | | Subject | Re: [v6 PATCH 00/21] x86: Enable User-Mode Instruction Prevention | From | Stas Sergeev <> | Date | Sat, 11 Mar 2017 00:37:19 +0300 |
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11.03.2017 00:04, Andy Lutomirski пишет: > On Fri, Mar 10, 2017 at 2:30 AM, Stas Sergeev <stsp@list.ru> wrote: >> 10.03.2017 05:41, Andy Lutomirski пишет: >> >>> On Wed, Mar 8, 2017 at 5:11 PM, Ricardo Neri >>> <ricardo.neri-calderon@linux.intel.com> wrote: >>>> On Wed, 2017-03-08 at 19:53 +0300, Stas Sergeev wrote: >>>>> 08.03.2017 19:46, Andy Lutomirski пишет: >>>>>>> No no, since I meant prot mode, this is not what I need. >>>>>>> I would never need to disable UMIP as to allow the >>>>>>> prot mode apps to do SLDT. Instead it would be good >>>>>>> to have an ability to provide a replacement for the dummy >>>>>>> emulation that is currently being proposed for kernel. >>>>>>> All is needed for this, is just to deliver a SIGSEGV. >>>>>> That's what I meant. Turning off FIXUP_UMIP would leave UMIP on but >>>>>> turn off the fixup, so you'd get a SIGSEGV indicating #GP (or a vm86 >>>>>> GP exit). >>>>> But then I am confused with the word "compat" in >>>>> your "COMPAT_MASK0_X86_UMIP_FIXUP" and >>>>> "sys_adjust_compat_mask(int op, int word, u32 mask);" >>>>> >>>>> Leaving UMIP on and only disabling a fixup doesn't >>>>> sound like a compat option to me. I would expect >>>>> compat to disable it completely. >>>> I guess that the _UMIP_FIXUP part makes it clear that emulation, not >>>> UMIP is disabled, allowing the SIGSEGV be delivered to the user space >>>> program. >>>> >>>> Would having a COMPAT_MASK0_X86_UMIP_FIXUP to disable emulation and a >>>> COMPAT_MASK0_X86_UMIP to disable UMIP make sense? >>>> >>>> Also, wouldn't having a COMPAT_MASK0_X86_UMIP to disable UMIP defeat its >>>> purpose? Applications could simply use this compat mask to bypass UMIP >>>> and gain access to the instructions it protects. >>>> >>> I was obviously extremely unclear. The point of the proposed syscall >>> is to let programs opt out of legacy features. >> I guess both "compat" and "legacy" are misleading >> here. Maybe these are "x86-specific" or "hypervisor-specific", >> but a mere enabling of UMIP doesn't immediately make >> the use of SLDT instruction a legacy IMHO. > Sure it is. :) Using SLDT from user mode is a legacy ability that > just happens to still work on existing CPUs and kernels. Once UMIP > goes in, it will officially be obsolete Yes, but the names you suggest, imply that "UMIP_FIXUP" is legacy or compat, which I find misleading because it have just appeared. Maybe something like "COMPAT_X86_UMIP_INSNS_EMU"?
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