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KVM: x86: Update number of entries for KVM_GET_CPUID2 on success, not failure

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Update cpuid->nent if and only if kvm_vcpu_ioctl_get_cpuid2() succeeds.
The sole caller copies @cpuid to userspace only on success, i.e. the
existing code effectively does nothing.

Arguably, KVM should report the number of entries when returning -E2BIG so
that userspace doesn't have to guess the size, but all other similar KVM
ioctls() don't report the size either, i.e. userspace is conditioned to
guess.

Suggested-by: Takahiro Itazuri <itazur@amazon.com>
Link: https://lore.kernel.org/all/20230410141820.57328-1-itazur@amazon.com
Link: https://lore.kernel.org/r/20230526210340.2799158-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2023-05-26 14:03:39 -07:00
parent 0d42522bde
commit ab322c43cc
1 changed files with 4 additions and 9 deletions
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13
arch/x86/kvm/cpuid.c
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@ -501,20 +501,15 @@ int kvm_vcpu_ioctl_get_cpuid2(struct kvm_vcpu *vcpu,
struct kvm_cpuid2 *cpuid,
struct kvm_cpuid_entry2 __user *entries)
{
int r;
r = -E2BIG;
if (cpuid->nent < vcpu->arch.cpuid_nent)
goto out;
r = -EFAULT;
return -E2BIG;
if (copy_to_user(entries, vcpu->arch.cpuid_entries,
vcpu->arch.cpuid_nent * sizeof(struct kvm_cpuid_entry2)))
goto out;
return 0;
return -EFAULT;
out:
cpuid->nent = vcpu->arch.cpuid_nent;
return r;
return 0;
}
/* Mask kvm_cpu_caps for @leaf with the raw CPUID capabilities of this CPU. */