2018-03-22 21:53 GMT+08:00 Andrew Cooper <andrew.cooper3@xxxxxxxxxx>: > On 22/03/18 13:39, Wanpeng Li wrote: >> 2018-03-22 20:38 GMT+08:00 Paolo Bonzini <pbonzini@xxxxxxxxxx>: >>> On 22/03/2018 12:04, Andrew Cooper wrote: >>>> We've got a Force Emulation Prefix (ud2a; .ascii "xen") for doing >>>> magic. Originally, this was used for PV guests to explicitly request an >>>> emulated CPUID, but I extended it to HVM guests for "emulate the next >>>> instruction", after we had some guest user => guest kernel privilege >>>> escalations because of incorrect emulation. >>> Wanpeng, why don't you add it behind a new kvm module parameter? :) >> Great point! I will have a try. Thanks Paolo and Andrew. :) > > Using the force emulation prefix requires intercepting #UD, which is in > general a BadThing(tm) for security. Therefore, we have a build time Yeah, however kvm intercepts and emulates #UD by default, should we add a new kvm module parameter to enable it and disable by default? Paolo. > configuration option to compile in support, and require that test > systems explicitly opt into using it via a command line parameter. > > http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=xen/arch/x86/hvm/hvm.c;h=db52312882205e65b32e587106ca795f4bfab2eb;hb=refs/heads/staging#l3741 > is the general #UD intercept handler if you want a reference. (You can Thanks Andrew, it is useful. :) In addition, I didn't see the test-memop-seg testcase has "Forced Emulation Prefix", when the prefix is added to each instruction in the testcase? Regards, Wanpeng Li
