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

[Steven Price]

On 17/06/2020 11:47, Marc Zyngier wrote:
> 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@xxxxxxx>
> > Signed-off-by: Steven Price <steven.price@xxxxxxx>
> > ---
> > The problematic chunk isn't visible in the diff, so reproduced here:
> >
> > ÂÂÂÂif (!kvm_arm_vcpu_sve_finalized(vcpu)) {
> > ÂÂÂÂÂÂÂ if (test_bit(KVM_ARM_VCPU_SVE, vcpu->arch.features)) {
> > ÂÂÂÂÂÂÂÂÂÂÂ ret = kvm_vcpu_enable_sve(vcpu);
> > ÂÂÂÂÂÂÂÂÂÂÂ if (ret)
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ goto out;
> > ÂÂÂÂÂÂÂ }
> > ÂÂÂÂ} else {
> > ÂÂÂÂÂÂÂ kvm_vcpu_reset_sve(vcpu);
> > ÂÂÂÂ}
> >
> > Âarch/arm64/kvm/reset.c | 10 +++++++---
> > Â1 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)
> > Â */
> > Âint kvm_reset_vcpu(struct kvm_vcpu *vcpu)
> > Â{
> > -ÂÂÂ int ret = -EINVAL;
> > +ÂÂÂ int ret;
> > ÂÂÂÂ bool loaded;
> > ÂÂÂÂ u32 pstate;
> >
> > @@ -269,15 +269,19 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
> >
> > ÂÂÂÂ if (test_bit(KVM_ARM_VCPU_PTRAUTH_ADDRESS, vcpu->arch.features) ||
> > ÂÂÂÂÂÂÂÂ test_bit(KVM_ARM_VCPU_PTRAUTH_GENERIC, vcpu->arch.features)) {
> > -ÂÂÂÂÂÂÂ if (kvm_vcpu_enable_ptrauth(vcpu))
> > +ÂÂÂÂÂÂÂ if (kvm_vcpu_enable_ptrauth(vcpu)) {
> > +ÂÂÂÂÂÂÂÂÂÂÂ ret = -EINVAL;
> > ÂÂÂÂÂÂÂÂÂÂÂÂ goto out;
> > +ÂÂÂÂÂÂÂ }
> > ÂÂÂÂ }
> >
> > ÂÂÂÂ switch (vcpu->arch.target) {
> > ÂÂÂÂ default:
> > ÂÂÂÂÂÂÂÂ if (test_bit(KVM_ARM_VCPU_EL1_32BIT, vcpu->arch.features)) {
> > -ÂÂÂÂÂÂÂÂÂÂÂ if (!cpus_have_const_cap(ARM64_HAS_32BIT_EL1))
> > +ÂÂÂÂÂÂÂÂÂÂÂ if (cpus_have_const_cap(ARM64_HAS_32BIT_EL1)) {
>
> Do you really mean this? Seems counter-productive... :-(

Clearly not... I'm really not sure how I managed to screw that up so 
badly :(

I'm glad someone is awake!

Sorry about that,

Steve

> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ ret = -EINVAL;
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ goto out;
> > +ÂÂÂÂÂÂÂÂÂÂÂ }
> > ÂÂÂÂÂÂÂÂÂÂÂÂ pstate = VCPU_RESET_PSTATE_SVC;
> > ÂÂÂÂÂÂÂÂ } else {
> > ÂÂÂÂÂÂÂÂÂÂÂÂ pstate = VCPU_RESET_PSTATE_EL1;
>
> Thanks,
>
>  ÂÂÂÂÂÂÂ M.