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

From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	Xiaoyao Li <xiaoyao.li@intel.com>
Subject: Re: [PATCH v2 53/66] KVM: x86: Do kvm_cpuid_array capacity checks in terminal functions
Date: Tue, 03 Mar 2020 17:03:50 +0100	[thread overview]
Message-ID: <87d09tfms9.fsf@vitty.brq.redhat.com> (raw)
In-Reply-To: <20200302235709.27467-54-sean.j.christopherson@intel.com>

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