[PATCH] KVM: arm64: kvm_reset_vcpu() return code incorrect with SVE

[Steven Price]

If SVE is enabled then 'ret' can be assigned the return value of
kvm_vcpu_enable_sve() which may be 0 causing future "goto out" sites to
erroneously return 0 on failure rather than -EINVAL as expected.

Remove the initialisation of 'ret' and make setting the return value
explicit to avoid this situation in the future.

Fixes: 9a3cdf26e336 ("KVM: arm64/sve: Allow userspace to enable SVE for vcpus")
Reported-by: James Morse <james.mo...@arm.com>
Signed-off-by: Steven Price <steven.pr...@arm.com>
---
The problematic chunk isn't visible in the diff, so reproduced here:

        if (!kvm_arm_vcpu_sve_finalized(vcpu)) {
                if (test_bit(KVM_ARM_VCPU_SVE, vcpu->arch.features)) {
                        ret = kvm_vcpu_enable_sve(vcpu);
                        if (ret)
                                goto out;
                }
        } else {
                kvm_vcpu_reset_sve(vcpu);
        }

 arch/arm64/kvm/reset.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
index d3b209023727..f1057603b756 100644
--- a/arch/arm64/kvm/reset.c
+++ b/arch/arm64/kvm/reset.c
@@ -245,7 +245,7 @@ static int kvm_vcpu_enable_ptrauth(struct kvm_vcpu *vcpu)
  */
 int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
 {
-       int ret = -EINVAL;
+       int ret;
        bool loaded;
        u32 pstate;
 
@@ -269,15 +269,19 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
 
        if (test_bit(KVM_ARM_VCPU_PTRAUTH_ADDRESS, vcpu->arch.features) ||
            test_bit(KVM_ARM_VCPU_PTRAUTH_GENERIC, vcpu->arch.features)) {
-               if (kvm_vcpu_enable_ptrauth(vcpu))
+               if (kvm_vcpu_enable_ptrauth(vcpu)) {
+                       ret = -EINVAL;
                        goto out;
+               }
        }
 
        switch (vcpu->arch.target) {
        default:
                if (test_bit(KVM_ARM_VCPU_EL1_32BIT, vcpu->arch.features)) {
-                       if (!cpus_have_const_cap(ARM64_HAS_32BIT_EL1))
+                       if (cpus_have_const_cap(ARM64_HAS_32BIT_EL1)) {
+                               ret = -EINVAL;
                                goto out;
+                       }
                        pstate = VCPU_RESET_PSTATE_SVC;
                } else {
                        pstate = VCPU_RESET_PSTATE_EL1;
-- 
2.20.1