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SubjectRe: [PATCH] KVM: arm64: kvm_reset_vcpu() return code incorrect with SVE
Hi Steven,

On 2020-06-17 11:43, Steven Price wrote:
> 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.morse@arm.com>
> Signed-off-by: Steven Price <steven.price@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)) {

Do you really mean this? Seems counter-productive... :-(

> + ret = -EINVAL;
> goto out;
> + }
> pstate = VCPU_RESET_PSTATE_SVC;
> } else {
> pstate = VCPU_RESET_PSTATE_EL1;

Thanks,

M.
--
Jazz is not dead. It just smells funny...

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