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

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Message-Id: <20211030000800.3065132-9-seanjc@google.com>
Date:   Fri, 29 Oct 2021 17:08:00 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     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>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        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>
Subject: [PATCH v2 8/8] KVM: x86: Add checks for reserved-to-zero Hyper-V
 hypercall fields

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.

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
-- 
2.33.1.1089.g2158813163f-goog