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Re: [PATCH v5 02/12] libx86: introduce helper to fetch cpuid leaf
- To: Roger Pau Monne <roger.pau@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 6 Dec 2021 15:31:18 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Ian Jackson <iwj@xxxxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Mon, 06 Dec 2021 14:31:43 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 29.11.2021 16:33, Roger Pau Monne wrote:
> Introduce a helper based on the current Xen guest_cpuid code in order
> to fetch a cpuid leaf from a policy. The newly introduced function in
> cpuid.c should not be directly called and instead the provided
> x86_cpuid_get_leaf macro should be used that will properly deal with
> const and non-const inputs.
>
> Also add a test to check that the introduced helper doesn't go over
> the bounds of the policy.
>
> Note the code in x86_cpuid_copy_from_buffer is not switched to use the
> new function because of the boundary checks against the max fields of
> the policy, which might not be properly set at the point where
> x86_cpuid_copy_from_buffer get called, for example when filling an
> empty policy from scratch.
>
> Suggested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> Regarding safety of the usage of array_access_nospec to obtain a
> pointer to an element of an array, there are already other instances
> of this usage, for example in viridian_time_wrmsr, so I would assume
> this is fine.
I wonder what it is that you think one might be concerned about. Such
pointer retrieval is no different from an actual array access imo.
Jan
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