KVM: s390: Fix cleanup in kvm_s390_pv_create_cpu()

If creating a protected vCPU in kvm_s390_pv_create_cpu() fails,
kvm_s390_pv_destroy_cpu() was called, which checks whether the vCPU has
a PV handle and exits doing nothing otherwise. At that point, due to
not having created the protected vCPU, the PV handle will not be set,
and kvm_s390_pv_destroy_cpu() will do nothing, thus leaking the
allocated memory.

Fix by factoring out the code to free and reset a PV vCPU; call it from
kvm_s390_pv_destroy_cpu() and kvm_s390_pv_create_cpu().

Opportunistically fix the return value of kvm_s390_pv_destroy_cpu() in
case of errors: return -EIO instead if EIO.

Fixes: d4074324b07a ("KVM: s390: pv: avoid double free of sida page")
Reviewed-by: Steffen Eiden <seiden@linux.ibm.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Message-ID: <20260803124040.126471-14-imbrenda@linux.ibm.com>

1 files changed, 21 insertions, 20 deletions

diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c
index dc204b521052..b02e0159d3cd 100644
--- a/arch/s390/kvm/pv.c
+++ b/arch/s390/kvm/pv.c
@@ -244,6 +244,24 @@ static void kvm_s390_clear_pv_state(struct kvm *kvm)
 	kvm->arch.pv.stor_var = NULL;
 }
 
+static void kvm_s390_pv_dispose_cpu(struct kvm_vcpu *vcpu, bool free_stor_base)
+{
+	if (free_stor_base)
+		free_pages(vcpu->arch.pv.stor_base, get_order(uv_info.guest_cpu_stor_len));
+	free_page((unsigned long)sida_addr(vcpu->arch.sie_block));
+	vcpu->arch.sie_block->pv_handle_cpu = 0;
+	vcpu->arch.sie_block->pv_handle_config = 0;
+	memset(&vcpu->arch.pv, 0, sizeof(vcpu->arch.pv));
+	vcpu->arch.sie_block->sdf = 0;
+	/*
+	 * The sidad field (for sdf == 2) is now the gbea field (for sdf == 0).
+	 * Use the reset value of gbea to avoid leaking the kernel pointer of
+	 * the just freed sida.
+	 */
+	vcpu->arch.sie_block->gbea = 1;
+	kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
+}
+
 int kvm_s390_pv_destroy_cpu(struct kvm_vcpu *vcpu, u16 *rc, u16 *rrc)
 {
 	int cc;
@@ -258,24 +276,9 @@ int kvm_s390_pv_destroy_cpu(struct kvm_vcpu *vcpu, u16 *rc, u16 *rrc)
 	WARN_ONCE(cc, "protvirt destroy cpu failed rc %x rrc %x", *rc, *rrc);
 
 	/* Intended memory leak for something that should never happen. */
-	if (!cc)
-		free_pages(vcpu->arch.pv.stor_base,
-			   get_order(uv_info.guest_cpu_stor_len));
-
-	free_page((unsigned long)sida_addr(vcpu->arch.sie_block));
-	vcpu->arch.sie_block->pv_handle_cpu = 0;
-	vcpu->arch.sie_block->pv_handle_config = 0;
-	memset(&vcpu->arch.pv, 0, sizeof(vcpu->arch.pv));
-	vcpu->arch.sie_block->sdf = 0;
-	/*
-	 * The sidad field (for sdf == 2) is now the gbea field (for sdf == 0).
-	 * Use the reset value of gbea to avoid leaking the kernel pointer of
-	 * the just freed sida.
-	 */
-	vcpu->arch.sie_block->gbea = 1;
-	kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
+	kvm_s390_pv_dispose_cpu(vcpu, !cc);
 
-	return cc ? EIO : 0;
+	return cc ? -EIO : 0;
 }
 
 int kvm_s390_pv_create_cpu(struct kvm_vcpu *vcpu, u16 *rc, u16 *rrc)
@@ -319,9 +322,7 @@ int kvm_s390_pv_create_cpu(struct kvm_vcpu *vcpu, u16 *rc, u16 *rrc)
 		     uvcb.header.rrc);
 
 	if (cc) {
-		u16 dummy;
-
-		kvm_s390_pv_destroy_cpu(vcpu, &dummy, &dummy);
+		kvm_s390_pv_dispose_cpu(vcpu, true);
 		return -EIO;
 	}