linux-kernel - Re: [PATCH AUTOSEL 5.16 07/28] x86/kvm/fpu: Limit guest user

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Date:   Tue, 1 Mar 2022 21:22:10 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sasha Levin <sashal@...nel.org>, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Cc:     Leonardo Bras <leobras@...hat.com>, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        x86@...nel.org, chang.seok.bae@...el.com, luto@...nel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH AUTOSEL 5.16 07/28] x86/kvm/fpu: Limit guest
 user_xfeatures to supported bits of XCR0

On 3/1/22 21:13, Sasha Levin wrote:
> diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
> index d28829403ed08..6ac01f9828530 100644
> --- a/arch/x86/kernel/fpu/xstate.c
> +++ b/arch/x86/kernel/fpu/xstate.c
> @@ -1563,7 +1563,10 @@ static int fpstate_realloc(u64 xfeatures, unsigned int ksize,
>   		fpregs_restore_userregs();
>   
>   	newfps->xfeatures = curfps->xfeatures | xfeatures;
> -	newfps->user_xfeatures = curfps->user_xfeatures | xfeatures;
> +
> +	if (!guest_fpu)
> +		newfps->user_xfeatures = curfps->user_xfeatures | xfeatures;
> +
>   	newfps->xfd = curfps->xfd & ~xfeatures;
>   
>   	curfps = fpu_install_fpstate(fpu, newfps);
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index bf18679757c70..875dce4aa2d28 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -276,6 +276,8 @@ static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
>   	vcpu->arch.guest_supported_xcr0 =
>   		cpuid_get_supported_xcr0(vcpu->arch.cpuid_entries, vcpu->arch.cpuid_nent);
>   
> +	vcpu->arch.guest_fpu.fpstate->user_xfeatures = vcpu->arch.guest_supported_xcr0;
> +
>   	kvm_update_pv_runtime(vcpu);
>   
>   	vcpu->arch.maxphyaddr = cpuid_query_maxphyaddr(vcpu);

Leonardo, was this also buggy in 5.16?  (I should have asked for a Fixes 
tag...).

Paolo