Re: [PATCH] KVM: x86: fix out-of-bounds write in KVM_GET_EMULATED_CPUID (CVE-2019-19332)

[Borislav Petkov]

On Wed, Dec 04, 2019 at 12:20:12PM +0100, Paolo Bonzini wrote:
> The bounds check was present in KVM_GET_SUPPORTED_CPUID but not
> KVM_GET_EMULATED_CPUID.
> 
> Reported-by: syzbot+e3f4897236c4eeb8af4f@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: 84cffe499b94 ("kvm: Emulate MOVBE", 2013-10-29)
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
>  arch/x86/kvm/cpuid.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 813a4d2e5c0c..cfafa320a8cf 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -504,7 +504,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_entry2 *entry, u32 function,
>  
>  	r = -E2BIG;
>  
> -	if (*nent >= maxnent)
> +	if (WARN_ON(*nent >= maxnent))
>  		goto out;
>  
>  	do_host_cpuid(entry, function, 0);
> @@ -815,6 +815,9 @@ static inline int __do_cpuid_func(struct kvm_cpuid_entry2 *entry, u32 function,
>  static int do_cpuid_func(struct kvm_cpuid_entry2 *entry, u32 func,
>  			 int *nent, int maxnent, unsigned int type)
>  {
> +	if (*nent >= maxnent)
> +		return -E2BIG;
> +
>  	if (type == KVM_GET_EMULATED_CPUID)
>  		return __do_cpuid_func_emulated(entry, func, nent, maxnent);
>  
> -- 

Whoops. ;-\

Thanks for the fix Paolo!

-- 
Regards/Gruss,
    Boris.

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