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    Subject[PATCH v2 05/66] KVM: x86: Check userapce CPUID array size after validating sub-leaf
    Date
    Verify that the next sub-leaf of CPUID 0x4 (or 0x8000001d) is valid
    before rejecting the entire KVM_GET_SUPPORTED_CPUID due to insufficent
    space in the userspace array.

    Note, although this is technically a bug, it's not visible to userspace
    as KVM_GET_SUPPORTED_CPUID is guaranteed to fail on KVM_CPUID_SIGNATURE,
    which is hardcoded to be added after the affected leafs. The real
    motivation for the change is to tightly couple the nent/maxnent and
    do_host_cpuid() sequences in preparation for future cleanup.

    Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
    Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
    ---
    arch/x86/kvm/cpuid.c | 6 +++---
    1 file changed, 3 insertions(+), 3 deletions(-)

    diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
    index 11d5f311ef10..e5cf1e0cf84a 100644
    --- a/arch/x86/kvm/cpuid.c
    +++ b/arch/x86/kvm/cpuid.c
    @@ -552,12 +552,12 @@ static inline int __do_cpuid_func(struct kvm_cpuid_entry2 *entry, u32 function,

    /* read more entries until cache_type is zero */
    for (i = 1; ; ++i) {
    - if (*nent >= maxnent)
    - goto out;
    -
    cache_type = entry[i - 1].eax & 0x1f;
    if (!cache_type)
    break;
    +
    + if (*nent >= maxnent)
    + goto out;
    do_host_cpuid(&entry[i], function, i);
    ++*nent;
    }
    --
    2.24.1
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