KVM: x86: Get the number of Hyper-V sparse banks from the VARHEAD field

Get the number of sparse banks from the VARHEAD field, which the guest is
required to provide as "The size of a variable header, in QWORDS.", where
the variable header is:

  Variable Header Bytes = {Total Header Bytes - sizeof(Fixed Header)}
                          rounded up to nearest multiple of 8
  Variable HeaderSize = Variable Header Bytes / 8

In other words, the VARHEAD should match the number of sparse banks.
Keep the manual count as a sanity check, but otherwise rely on the field
so as to more closely align with the logic defined in the TLFS and to
allow for future cleanups.

Tweak the tracepoint output to use "rep_cnt" instead of simply "cnt" now
that there is also "var_cnt".

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20211207220926.718794-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 21 insertions, 14 deletions

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 0bc7488f2b39..d02398c7a22d 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -1746,6 +1746,7 @@ struct kvm_hv_hcall {
 	u64 ingpa;
 	u64 outgpa;
 	u16 code;
+	u16 var_cnt;
 	u16 rep_cnt;
 	u16 rep_idx;
 	bool fast;
@@ -1765,7 +1766,6 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc, bool
 	unsigned long *vcpu_mask;
 	u64 valid_bank_mask;
 	u64 sparse_banks[64];
-	int sparse_banks_len;
 	bool all_cpus;
 
 	if (!ex) {
@@ -1815,24 +1815,28 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc, bool
 		all_cpus = flush_ex.hv_vp_set.format !=
 			HV_GENERIC_SET_SPARSE_4K;
 
-		sparse_banks_len = bitmap_weight((unsigned long *)&valid_bank_mask, 64);
+		if (hc->var_cnt != bitmap_weight((unsigned long *)&valid_bank_mask, 64))
+			return HV_STATUS_INVALID_HYPERCALL_INPUT;
 
-		if (!sparse_banks_len && !all_cpus)
+		if (!hc->var_cnt && !all_cpus)
 			goto ret_success;
 
 		if (!all_cpus) {
 			if (hc->fast) {
-				if (sparse_banks_len > HV_HYPERCALL_MAX_XMM_REGISTERS - 1)
+				if (hc->var_cnt > HV_HYPERCALL_MAX_XMM_REGISTERS - 1)
 					return HV_STATUS_INVALID_HYPERCALL_INPUT;
-				for (i = 0; i < sparse_banks_len; i += 2) {
+				for (i = 0; i < hc->var_cnt; i += 2) {
 					sparse_banks[i] = sse128_lo(hc->xmm[i / 2 + 1]);
 					sparse_banks[i + 1] = sse128_hi(hc->xmm[i / 2 + 1]);
 				}
 			} else {
+				if (hc->var_cnt > 64)
+					return HV_STATUS_INVALID_HYPERCALL_INPUT;
+
 				gpa = hc->ingpa + offsetof(struct hv_tlb_flush_ex,
 							   hv_vp_set.bank_contents);
 				if (unlikely(kvm_read_guest(kvm, gpa, sparse_banks,
-							    sparse_banks_len *
+							    hc->var_cnt *
 							    sizeof(sparse_banks[0]))))
 					return HV_STATUS_INVALID_HYPERCALL_INPUT;
 			}
@@ -1888,7 +1892,6 @@ static u64 kvm_hv_send_ipi(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc, bool
 	unsigned long *vcpu_mask;
 	unsigned long valid_bank_mask;
 	u64 sparse_banks[64];
-	int sparse_banks_len;
 	u32 vector;
 	bool all_cpus;
 
@@ -1921,22 +1924,25 @@ static u64 kvm_hv_send_ipi(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc, bool
 
 		vector = send_ipi_ex.vector;
 		valid_bank_mask = send_ipi_ex.vp_set.valid_bank_mask;
-		sparse_banks_len = bitmap_weight(&valid_bank_mask, 64) *
-			sizeof(sparse_banks[0]);
-
 		all_cpus = send_ipi_ex.vp_set.format == HV_GENERIC_SET_ALL;
 
+		if (hc->var_cnt != bitmap_weight(&valid_bank_mask, 64))
+			return HV_STATUS_INVALID_HYPERCALL_INPUT;
+
 		if (all_cpus)
 			goto check_and_send_ipi;
 
-		if (!sparse_banks_len)
+		if (!hc->var_cnt)
 			goto ret_success;
 
+		if (hc->var_cnt > 64)
+			return HV_STATUS_INVALID_HYPERCALL_INPUT;
+
 		if (kvm_read_guest(kvm,
 				   hc->ingpa + offsetof(struct hv_send_ipi_ex,
 							vp_set.bank_contents),
 				   sparse_banks,
-				   sparse_banks_len))
+				   hc->var_cnt * sizeof(sparse_banks[0])))
 			return HV_STATUS_INVALID_HYPERCALL_INPUT;
 	}
 
@@ -2194,13 +2200,14 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
 	}
 
 	hc.code = hc.param & 0xffff;
+	hc.var_cnt = (hc.param & HV_HYPERCALL_VARHEAD_MASK) >> HV_HYPERCALL_VARHEAD_OFFSET;
 	hc.fast = !!(hc.param & HV_HYPERCALL_FAST_BIT);
 	hc.rep_cnt = (hc.param >> HV_HYPERCALL_REP_COMP_OFFSET) & 0xfff;
 	hc.rep_idx = (hc.param >> HV_HYPERCALL_REP_START_OFFSET) & 0xfff;
 	hc.rep = !!(hc.rep_cnt || hc.rep_idx);
 
-	trace_kvm_hv_hypercall(hc.code, hc.fast, hc.rep_cnt, hc.rep_idx,
-			       hc.ingpa, hc.outgpa);
+	trace_kvm_hv_hypercall(hc.code, hc.fast, hc.var_cnt, hc.rep_cnt,
+			       hc.rep_idx, hc.ingpa, hc.outgpa);
 
 	if (unlikely(!hv_check_hypercall_access(hv_vcpu, hc.code))) {
 		ret = HV_STATUS_ACCESS_DENIED;