Re: CVS: cvs.openbsd.org: src

[Anton Lindqvist]

On Mon, Apr 24, 2023 at 10:53:57AM -0600, Dave Voutila wrote:
> CVSROOT:      /cvs
> Module name:  src
> Changes by:   d...@cvs.openbsd.org    2023/04/24 10:53:57
> 
> Modified files:
>       sys/arch/amd64/amd64: vmm.c 
> 
> Log message:
> vmm(4): allow guests to enable and use supervisor IBT.
> 
> Why should hosts have all the fun? Conditionally unmask the cpuid
> bits for IBT and allow r/w access to the supervisor CET msr.
> 
> Will need revisiting when we introduce usage of userland CET msr.
> 
> ok marlkin@

Running on older hardware where CET is not enumerated causes guests to
panic in cpu_fix_msrs() during RDMSR 0x6a2.

diff --git sys/arch/amd64/amd64/vmm.c sys/arch/amd64/amd64/vmm.c
index 42ac8007029..35b05033cdc 100644
--- sys/arch/amd64/amd64/vmm.c
+++ sys/arch/amd64/amd64/vmm.c
@@ -7059,7 +7059,7 @@ vmm_handle_cpuid(struct vcpu *vcpu)
                                *rcx &= ~SEFF0ECX_PKU;
 
                        /* Expose IBT bit if we've enabled CET on the host. */
-                       if (rcr4() | CR4_CET)
+                       if (rcr4() & CR4_CET)
                                *rdx |= SEFF0EDX_IBT;
                        else
                                *rdx &= ~SEFF0EDX_IBT;