Re: [PATCH] KVM: vmx: VMXOFF emulation in vm86 should cause #UD

[Paolo Bonzini <pbonzini@redhat.com>]

Il 29/08/2014 10:52, Nadav Amit ha scritto:
> > Patch looks good, but where is the check that MOD == 3 in the "case
> > RMExt"?  Am I just not seeing it?
> 
> This seems to be part of the “case GroupDual”.

GroupDual handles it, but the EXT() macro you're using is exactly what 
you want:

#define RMExt       (4<<15)     /* Opcode extension in ModRM r/m if mod == 3 */

I guess what's missing is

------------------ 8< ------------------
Subject: [PATCH] Check ModRM for RMExt

Some group7 extensions are only defined for mod==3.  Check this and
reject emulation if mod!=3.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 56657b0bb3bb..d472e4d50e3c 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -4360,6 +4360,8 @@ done_prefixes:
 				opcode = opcode.u.gdual->mod012[goffset];
 			break;
 		case RMExt:
+			if ((ctxt->modrm >> 6) == 3)
+				return EMULATION_FAILED;
 			goffset = ctxt->modrm & 7;
 			opcode = opcode.u.group[goffset];
 			break;

What do you think?

Paolo