Re: [PATCH v4 0/4] Relax canonical checks on some arch msrs

[Maxim Levitsky]

On Fri, 2024-09-06 at 18:18 -0400, Maxim Levitsky wrote:
> Recently we came up upon a failure where likely the guest writes
> 0xff4547ceb1600000 to MSR_KERNEL_GS_BASE and later on, qemu
> sets this value via KVM_PUT_MSRS, and is rejected by the
> kernel, likely due to not being canonical in 4 level paging.
> 
> One of the way to trigger this is to make the guest enter SMM,
> which causes paging to be disabled, which SMM bios re-enables
> but not the whole 5 level. MSR_KERNEL_GS_BASE on the other
> hand continues to contain old value.
> 
> I did some reverse engineering and to my surprise I found out
> that both Intel and AMD indeed ignore CR4.LA57 when doing
> canonical checks on this and other msrs and/or other arch
> registers (like GDT base) which contain linear addresses.
> 
> V2: addressed a very good feedback from Chao Gao. Thanks!
> 
> V3: also fix the nested VMX, and also fix the
> MSR_IA32_SYSENTER_EIP / MSR_IA32_SYSENTER_ESP
> 
> V4:
>   - added PT and PEBS msrs
>   - corrected emulation of SGDT/SIDT/STR/SLDT instructions
>   - corrected canonical checks for TLB invalidation instructions
> 
> Best regards,
> 	Maxim Levitsky
> 
> Maxim Levitsky (4):
>   KVM: x86: drop x86.h include from cpuid.h
>   KVM: x86: implement emul_is_noncanonical_address using
>     is_noncanonical_address
>   KVM: x86: model canonical checks more precisely
>   KVM: nVMX: fix canonical check of vmcs12 HOST_RIP
> 
>  arch/x86/kvm/cpuid.h         |  1 -
>  arch/x86/kvm/emulate.c       | 15 ++++++-----
>  arch/x86/kvm/kvm_emulate.h   |  5 ++++
>  arch/x86/kvm/mmu.h           |  1 +
>  arch/x86/kvm/mmu/mmu.c       |  2 +-
>  arch/x86/kvm/vmx/hyperv.c    |  1 +
>  arch/x86/kvm/vmx/nested.c    | 35 +++++++++++++++++---------
>  arch/x86/kvm/vmx/pmu_intel.c |  2 +-
>  arch/x86/kvm/vmx/sgx.c       |  5 ++--
>  arch/x86/kvm/vmx/vmx.c       |  4 +--
>  arch/x86/kvm/x86.c           | 13 +++++++---
>  arch/x86/kvm/x86.h           | 49 ++++++++++++++++++++++++++++++++++--
>  12 files changed, 102 insertions(+), 31 deletions(-)
> 
> -- 
> 2.26.3
> 
> 

Hi,
A very gentle ping on this patch series.

Best regards,
	Maxim Levitsky