Re: [PATCH 03/14] KVM: x86: nSVM: test eax for 4K alignment for GP errata workaround

[Paolo Bonzini]

On 14/09/21 17:48, Maxim Levitsky wrote:
> GP SVM errata workaround made the #GP handler always emulate
> the SVM instructions.
>
> However these instructions #GP in case the operand is not 4K aligned,
> but the workaround code didn't check this and we ended up
> emulating these instructions anyway.
>
> This is only an emulation accuracy check bug as there is no harm for
> KVM to read/write unaligned vmcb images.
>
> Fixes: 82a11e9c6fa2 ("KVM: SVM: Add emulation support for #GP triggered by SVM instructions")
>
> Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
> ---
>   arch/x86/kvm/svm/svm.c | 4 ++++
>   1 file changed, 4 insertions(+)
>
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index b2e710a3fff6..6645542df9bd 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -2224,6 +2224,10 @@ static int gp_interception(struct kvm_vcpu *vcpu)
>   	if (error_code)
>   		goto reinject;
>   
> +	/* All SVM instructions expect page aligned RAX */
> +	if (svm->vmcb->save.rax & ~PAGE_MASK)
> +		goto reinject;
> +
>   	/* Decode the instruction for usage later */
>   	if (x86_decode_emulated_instruction(vcpu, 0, NULL, 0) != EMULATION_OK)
>   		goto reinject;


Queued, thanks.

Paolo