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

Sean Christopherson
2021-10-30T00:09:14Z

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@google.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