diff mbox series

[v2,04/13] KVM: selftests: Assert that vcpu_{g,s}et_reg() won't truncate

Message ID 20240911204158.2034295-5-seanjc@google.com
State Changes Requested
Headers show
Series KVM: selftests: Morph max_guest_mem to mmu_stress | expand

Commit Message

Sean Christopherson Sept. 11, 2024, 8:41 p.m. UTC 
Assert that the the register being read/written by vcpu_{g,s}et_reg() is
no larger than a uint64_t, i.e. that a selftest isn't unintentionally
truncating the value being read/written.

Ideally, the assert would be done at compile-time, but that would limit
the checks to hardcoded accesses and/or require fancier compile-time
assertion infrastructure to filter out dynamic usage.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 tools/testing/selftests/kvm/include/kvm_util.h | 4 ++++
 1 file changed, 4 insertions(+)

Comments

Andrew Jones Sept. 12, 2024, 9:41 a.m. UTC | #1 
On Wed, Sep 11, 2024 at 01:41:49PM GMT, Sean Christopherson wrote:
> Assert that the the register being read/written by vcpu_{g,s}et_reg() is
> no larger than a uint64_t, i.e. that a selftest isn't unintentionally
> truncating the value being read/written.
> 
> Ideally, the assert would be done at compile-time, but that would limit
> the checks to hardcoded accesses and/or require fancier compile-time
> assertion infrastructure to filter out dynamic usage.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>  tools/testing/selftests/kvm/include/kvm_util.h | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h
> index 429a7f003fe3..80230e49e35f 100644
> --- a/tools/testing/selftests/kvm/include/kvm_util.h
> +++ b/tools/testing/selftests/kvm/include/kvm_util.h
> @@ -683,6 +683,8 @@ static inline uint64_t vcpu_get_reg(struct kvm_vcpu *vcpu, uint64_t id)
>  	uint64_t val;
>  	struct kvm_one_reg reg = { .id = id, .addr = (uint64_t)&val };
>  
> +	TEST_ASSERT(KVM_REG_SIZE(id) <= sizeof(val), "Reg %lx too big", id);
> +
>  	vcpu_ioctl(vcpu, KVM_GET_ONE_REG, &reg);
>  	return val;
>  }
> @@ -690,6 +692,8 @@ static inline void vcpu_set_reg(struct kvm_vcpu *vcpu, uint64_t id, uint64_t val
>  {
>  	struct kvm_one_reg reg = { .id = id, .addr = (uint64_t)&val };
>  
> +	TEST_ASSERT(KVM_REG_SIZE(id) <= sizeof(val), "Reg %lx too big", id);
> +
>  	vcpu_ioctl(vcpu, KVM_SET_ONE_REG, &reg);
>  }
>  
> -- 
> 2.46.0.598.g6f2099f65c-goog
>

Reviewed-by: Andrew Jones <ajones@ventanamicro.com>

Shouldn't patches 3 and 4 come before patch 2 in this series?

Thanks,
drew
Sean Christopherson Sept. 12, 2024, 4:17 p.m. UTC | #2 
On Thu, Sep 12, 2024, Andrew Jones wrote:
> On Wed, Sep 11, 2024 at 01:41:49PM GMT, Sean Christopherson wrote:
> > Assert that the the register being read/written by vcpu_{g,s}et_reg() is
> > no larger than a uint64_t, i.e. that a selftest isn't unintentionally
> > truncating the value being read/written.
> > 
> > Ideally, the assert would be done at compile-time, but that would limit
> > the checks to hardcoded accesses and/or require fancier compile-time
> > assertion infrastructure to filter out dynamic usage.
> > 
> > Signed-off-by: Sean Christopherson <seanjc@google.com>
> > ---
> >  tools/testing/selftests/kvm/include/kvm_util.h | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h
> > index 429a7f003fe3..80230e49e35f 100644
> > --- a/tools/testing/selftests/kvm/include/kvm_util.h
> > +++ b/tools/testing/selftests/kvm/include/kvm_util.h
> > @@ -683,6 +683,8 @@ static inline uint64_t vcpu_get_reg(struct kvm_vcpu *vcpu, uint64_t id)
> >  	uint64_t val;
> >  	struct kvm_one_reg reg = { .id = id, .addr = (uint64_t)&val };
> >  
> > +	TEST_ASSERT(KVM_REG_SIZE(id) <= sizeof(val), "Reg %lx too big", id);
> > +
> >  	vcpu_ioctl(vcpu, KVM_GET_ONE_REG, &reg);
> >  	return val;
> >  }
> > @@ -690,6 +692,8 @@ static inline void vcpu_set_reg(struct kvm_vcpu *vcpu, uint64_t id, uint64_t val
> >  {
> >  	struct kvm_one_reg reg = { .id = id, .addr = (uint64_t)&val };
> >  
> > +	TEST_ASSERT(KVM_REG_SIZE(id) <= sizeof(val), "Reg %lx too big", id);
> > +
> >  	vcpu_ioctl(vcpu, KVM_SET_ONE_REG, &reg);
> >  }
> >  
> > -- 
> > 2.46.0.598.g6f2099f65c-goog
> >
> 
> Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
> 
> Shouldn't patches 3 and 4 come before patch 2 in this series?

Ideally, yes, but for this patch, it gets weird because the output param of
vcpu_reg_get() isn't actually restricted to a 64-bit value prior to patch 2.
E.g. if this patch were merged without that rework, then the assert would be
confusing and arguably flat out wrong.

As for the hack-a-fix, I deliberately ordered it after patch 2 so that it would
be easier for others to (try to) reproduce the bug.  I have no objection to
swapping 2 and 3 in the next version.
diff mbox series

Patch

diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h
index 429a7f003fe3..80230e49e35f 100644
--- a/tools/testing/selftests/kvm/include/kvm_util.h
+++ b/tools/testing/selftests/kvm/include/kvm_util.h
@@ -683,6 +683,8 @@  static inline uint64_t vcpu_get_reg(struct kvm_vcpu *vcpu, uint64_t id)
 	uint64_t val;
 	struct kvm_one_reg reg = { .id = id, .addr = (uint64_t)&val };
 
+	TEST_ASSERT(KVM_REG_SIZE(id) <= sizeof(val), "Reg %lx too big", id);
+
 	vcpu_ioctl(vcpu, KVM_GET_ONE_REG, &reg);
 	return val;
 }
@@ -690,6 +692,8 @@  static inline void vcpu_set_reg(struct kvm_vcpu *vcpu, uint64_t id, uint64_t val
 {
 	struct kvm_one_reg reg = { .id = id, .addr = (uint64_t)&val };
 
+	TEST_ASSERT(KVM_REG_SIZE(id) <= sizeof(val), "Reg %lx too big", id);
+
 	vcpu_ioctl(vcpu, KVM_SET_ONE_REG, &reg);
 }