Re: [Xen-devel] [PATCH V7 1/4] x86/mm: Add array_index_nospec to guest provided index values

[Jan Beulich <jbeulich@xxxxxxxx>]

On 08.01.2020 15:08, Alexandru Stefan ISAILA wrote:
> Changes since V6:
>       - Remove stray spaces
>       - Use ARRAY_SIZE(d->arch.altp2m_p2m) insead of MAX_ALTP2M.

I'm not utterly confused:

> --- a/xen/arch/x86/mm/mem_access.c
> +++ b/xen/arch/x86/mm/mem_access.c
> @@ -366,11 +366,13 @@ long p2m_set_mem_access(struct domain *d, gfn_t gfn, 
> uint32_t nr,
>  #ifdef CONFIG_HVM
>      if ( altp2m_idx )
>      {
> -        if ( altp2m_idx >= MAX_ALTP2M ||
> -             d->arch.altp2m_eptp[altp2m_idx] == mfn_x(INVALID_MFN) )
> +        if ( altp2m_idx >= min(ARRAY_SIZE(d->arch.altp2m_p2m), MAX_EPTP) ||
> +             d->arch.altp2m_eptp[array_index_nospec(altp2m_idx, MAX_EPTP)] ==
> +             mfn_x(INVALID_MFN) )
>              return -EINVAL;
>  
> -        ap2m = d->arch.altp2m_p2m[altp2m_idx];
> +        ap2m = d->arch.altp2m_p2m[array_index_nospec(altp2m_idx,
> +                                  ARRAY_SIZE(d->arch.altp2m_p2m))];

Why is this still not

        ap2m = array_access_nospec(d->arch.altp2m_p2m, altp2m_idx);

? What am I missing?

Jan

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