Re: [PATCH v2 53/66] KVM: x86: Do kvm_cpuid_array capacity checks in terminal functions

Vitaly Kuznetsov
2020-03-03T16:03:57Z

Sean Christopherson <sean.j.christopherson@intel.com> writes:

> Perform the capacity checks on the userspace provided kvm_cpuid_array
> in the lower __do_cpuid_func() and __do_cpuid_func_emulated().
> Pre-checking the array in do_cpuid_func() no longer adds value now that
> __do_cpuid_func() has been trimmed down to size, i.e. doesn't invoke a
> big pile of retpolined functions before doing anything useful.
>
> Note, __do_cpuid_func() already checks the array capacity via
> do_host_cpuid(), "moving" the check to __do_cpuid_func() simply means
> removing a WARN_ON().
>
> Suggested-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
> arch/x86/kvm/cpuid.c | 11 ++++++-----
> 1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index eebd7f613f67..f879fcbd6fb2 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -478,8 +478,12 @@ static struct kvm_cpuid_entry2 *do_host_cpuid(struct kvm_cpuid_array *array,
>
> static int __do_cpuid_func_emulated(struct kvm_cpuid_array *array, u32 func)
> {
> - struct kvm_cpuid_entry2 *entry = &array->entries[array->nent];
> + struct kvm_cpuid_entry2 *entry;
>
> + if (array->nent >= array->maxnent)
> + return -E2BIG;
> +
> + entry = &array->entries[array->nent];
> entry->function = func;
> entry->index = 0;
> entry->flags = 0;
> @@ -516,7 +520,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
> r = -E2BIG;
>
> entry = do_host_cpuid(array, function, 0);
> - if (WARN_ON(!entry))
> + if (!entry)
> goto out;
>
> switch (function) {
> @@ -787,9 +791,6 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
> static int do_cpuid_func(struct kvm_cpuid_array *array, u32 func,
> unsigned int type)
> {
> - if (array->nent >= array->maxnent)
> - return -E2BIG;
> -
> if (type == KVM_GET_EMULATED_CPUID)
> return __do_cpuid_func_emulated(array, func);

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>

--
Vitaly