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Re: [XEN RFC] x86/uaccess: remove __{put,get}_user_bad()


  • To: Federico Serafini <federico.serafini@xxxxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Thu, 21 Dec 2023 11:58:04 +0100
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  • Cc: consulting@xxxxxxxxxxx, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
  • Delivery-date: Thu, 21 Dec 2023 10:58:15 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 21.12.2023 11:53, Federico Serafini wrote:
> Remove declarations of __put_user_bad() and __get_user_bad()
> since they have no definition.
> Replace their uses with a break statement to address violations of
> MISRA C:2012 Rule 16.3 ("An unconditional `break' statement shall
> terminate every switch-clause").
> No functional change.
> 
> Signed-off-by: Federico Serafini <federico.serafini@xxxxxxxxxxx>
> ---
> Several violations of Rule 16.3 come from uses of macros
> get_unsafe_size() and put_unsafe_size().
> Looking at the macro definitions I found __get_user_bad() and 
> __put_user_bad().
> I was wondering if instead of just adding the break statement I can also 
> remove
> such functions which seem to not have a definition.

No, you can't. Try introducing a caller which "accidentally" uses the
wrong size. Without your change you'll observe the build failing (in
a somewhat obscure way, but still), while with your change bad code
will silently be generated.

Jan



 


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