linux-kernel - Re: [PATCH v2 8/8] KVM: x86: Add checks for reserved-to-zero Hyper-V hypercall fields

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Message-ID: <87v91cjhch.fsf@vitty.brq.redhat.com>
Date:   Mon, 01 Nov 2021 11:33:18 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-hyperv@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, Ajay Garg <ajaygargnsit@...il.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v2 8/8] KVM: x86: Add checks for reserved-to-zero
 Hyper-V hypercall fields

Sean Christopherson <seanjc@...gle.com> writes:

> Add checks for the three fields in Hyper-V's hypercall params that must
> be zero.  Per the TLFS, HV_STATUS_INVALID_HYPERCALL_INPUT is returned if
> "A reserved bit in the specified hypercall input value is non-zero."
>
> Note, the TLFS has an off-by-one bug for the last reserved field, which
> it defines as being bits 64:60.  The same section states "The input field
> 64-bit value called a hypercall input value.", i.e. bit 64 doesn't
> exist.

This version are you looking at? I can't see this issue in 6.0b

>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/hyperv.c             | 5 +++++
>  include/asm-generic/hyperv-tlfs.h | 6 ++++++
>  2 files changed, 11 insertions(+)
>
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index ad455df850c9..1cdcf3ad5684 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -2228,6 +2228,11 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
>  		goto hypercall_complete;
>  	}
>  
> +	if (unlikely(hc.param & HV_HYPERCALL_RSVD_MASK)) {
> +		ret = HV_STATUS_INVALID_HYPERCALL_INPUT;
> +		goto hypercall_complete;
> +	}
> +
>  	if (hc.fast && is_xmm_fast_hypercall(&hc)) {
>  		if (unlikely(hv_vcpu->enforce_cpuid &&
>  			     !(hv_vcpu->cpuid_cache.features_edx &
> diff --git a/include/asm-generic/hyperv-tlfs.h b/include/asm-generic/hyperv-tlfs.h
> index 1ba8e6da4427..92b9ce5882f8 100644
> --- a/include/asm-generic/hyperv-tlfs.h
> +++ b/include/asm-generic/hyperv-tlfs.h
> @@ -183,11 +183,17 @@ enum HV_GENERIC_SET_FORMAT {
>  #define HV_HYPERCALL_FAST_BIT		BIT(16)
>  #define HV_HYPERCALL_VARHEAD_OFFSET	17
>  #define HV_HYPERCALL_VARHEAD_MASK	GENMASK_ULL(26, 17)
> +#define HV_HYPERCALL_RSVD0_MASK		GENMASK_ULL(31, 27)
>  #define HV_HYPERCALL_REP_COMP_OFFSET	32
>  #define HV_HYPERCALL_REP_COMP_1		BIT_ULL(32)
>  #define HV_HYPERCALL_REP_COMP_MASK	GENMASK_ULL(43, 32)
> +#define HV_HYPERCALL_RSVD1_MASK		GENMASK_ULL(47, 44)
>  #define HV_HYPERCALL_REP_START_OFFSET	48
>  #define HV_HYPERCALL_REP_START_MASK	GENMASK_ULL(59, 48)
> +#define HV_HYPERCALL_RSVD2_MASK		GENMASK_ULL(63, 60)
> +#define HV_HYPERCALL_RSVD_MASK		(HV_HYPERCALL_RSVD0_MASK | \
> +					 HV_HYPERCALL_RSVD1_MASK | \
> +					 HV_HYPERCALL_RSVD2_MASK)
>  
>  /* hypercall status code */
>  #define HV_STATUS_SUCCESS			0

Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>

-- 
Vitaly